Fast, lightweight (~5 KB gzipped) and reusable data fetching

"fetchff" stands for "fetch fast & flexibly"

Why?

This is a high level library to extend the functionality of native fetch() with everything necessary and no overhead, so to wrap and reuse common patterns and functionalities in a simple and declarative manner. It is designed to be used in high-throughput, high-performance applications.

Also, managing multitude of API connections in large applications can be complex, time-consuming and hard to scale. fetchff simplifies the process by offering a simple, declarative approach to API handling using Repository Pattern. It reduces the need for extensive setup, middlewares, retries, custom caching, and heavy plugins, and lets developers focus on data handling and application logic.

Click to expand

Some of challenges with Native Fetch that fetchff solves:

• Error Status Handling: Fetch does not throw errors for HTTP error statuses, making it difficult to distinguish between successful and failed requests based on status codes alone.
• Error Visibility: Error responses with status codes like 404 or 500 are not automatically propagated as exceptions, which can lead to inconsistent error handling.
• No Built-in Retry Mechanism: Native fetch() lacks built-in support for retrying requests. Developers need to implement custom retry logic to handle transient errors or intermittent failures, which can be cumbersome and error-prone.
• Network Errors Handling: Native fetch() only rejects the Promise for network errors or failure to reach the server. Issues such as timeout errors or server unavailability do not trigger rejection by default, which can complicate error management.
• Limited Error Information: The error information provided by native fetch() is minimal, often leaving out details such as the request headers, status codes, or response bodies. This can make debugging more difficult, as there's limited visibility into what went wrong.
• Lack of Interceptors: Native fetch() does not provide a built-in mechanism for intercepting requests or responses. Developers need to manually manage request and response processing, which can lead to repetitive code and less maintainable solutions.
• No Built-in Caching: Native fetch() does not natively support caching of requests and responses. Implementing caching strategies requires additional code and management, potentially leading to inconsistencies and performance issues.

To address these challenges, the fetchf() provides several enhancements:

1. Consistent Error Handling:

   • In JavaScript, the native fetch() function does not reject the Promise for HTTP error statuses such as 404 (Not Found) or 500 (Internal Server Error). Instead, fetch() resolves the Promise with a Response object, where the ok property indicates the success of the request. If the request encounters a network error or fails due to other issues (e.g., server downtime), fetch() will reject the Promise.
   • The fetchff plugin aligns error handling with common practices and makes it easier to manage errors consistently by rejecting erroneous status codes.

2. Enhanced Retry Mechanism:

   • Retry Configuration: You can configure the number of retries, delay between retries, and exponential backoff for failed requests. This helps to handle transient errors effectively.
   • Custom Retry Logic: The shouldRetry asynchronous function allows for custom retry logic based on the error from response.error and attempt count, providing flexibility to handle different types of failures.
   • Retry Conditions: Errors are only retried based on configurable retry conditions, such as specific HTTP status codes or error types.

3. Improved Error Visibility:

   • Error Wrapping: The createApiFetcher() and fetchf() wrap errors in a custom ResponseError class, which provides detailed information about the request and response. This makes debugging easier and improves visibility into what went wrong.

4. Extended settings:

   • Check Settings table for more information about all settings.

✔️ Benefits

✅ Lightweight: Minimal code footprint of ~4KB gzipped for managing extensive APIs.

✅ High-Performance: Optimized for speed and efficiency, ensuring fast and reliable API interactions.

✅ Secure: Secure by default rather than "permissive by default", with built-in sanitization mechanisms.

✅ Immutable: Every request has its own instance.

✅ Isomorphic: Compatible with Node.js, Deno and modern browsers.

✅ Type Safe: Strongly typed and written in TypeScript.

✅ Scalable: Easily scales from a few calls to complex API networks with thousands of APIs.

✅ Tested: Battle tested in large projects, fully covered by unit tests.

✅ Customizable: Fully compatible with a wide range configuration options, allowing for flexible and detailed request customization.

✅ Responsible Defaults: All settings are opt-in.

✅ Framework Independent: Pure JavaScript solution, compatible with any framework or library, both client and server side.

✅ Browser and Node.js 18+ Compatible: Works flawlessly in both modern browsers and Node.js environments.

✅ Maintained: Since 2021 publicly through Github.

✔️ Features

• Smart Retry Mechanism: Features exponential backoff for intelligent error handling and retry mechanisms.
• Request Deduplication: Set the time during which requests are deduplicated (treated as same request).
• Cache Management: Dynamically manage cache with configurable expiration, custom keys, and selective invalidation.
• Network Revalidation: Automatically revalidate data on window focus and network reconnection for fresh data.
• Dynamic URLs Support: Easily manage routes with dynamic parameters, such as /user/:userId.
• Error Handling: Flexible error management at both global and individual request levels.
• Request Cancellation: Utilizes AbortController to cancel previous requests automatically.
• Adaptive Timeouts: Smart timeout adjustment based on connection speed for optimal user experience.
• Fetching Strategies: Handle failed requests with various strategies - promise rejection, silent hang, soft fail, or default response.
• Requests Chaining: Easily chain multiple requests using promises for complex API interactions.
• Native fetch() Support: Utilizes the built-in fetch() API, providing a modern and native solution for making HTTP requests.
• Custom Interceptors: Includes onRequest, onResponse, and onError interceptors for flexible request and response handling.

✔️ Install

Using NPM:

npm install fetchff

Using Pnpm:

pnpm install fetchff

Using Yarn:

yarn add fetchff

✔️ API

Standalone usage

fetchf(url, config)

Alias: fetchff(url, config)

A simple function that wraps the native fetch() and adds extra features like retries and better error handling. Use fetchf() directly for quick, enhanced requests - no need to set up createApiFetcher(). It works independently and is easy to use in any codebase.

Example

import { fetchf } from 'fetchff';

const { data, error } = await fetchf('/api/user-details', {
  timeout: 5000,
  cancellable: true,
  retry: { retries: 3, delay: 2000 },
  // Specify some other settings here... The fetch() settings work as well...
});

Global Configuration

getDefaultConfig()

Click to expand

Returns the current global default configuration used for all requests. This is useful for inspecting or debugging the effective global settings.

import { getDefaultConfig } from 'fetchff';

// Retrieve the current global default config
const config = getDefaultConfig();
console.log('Current global fetchff config:', config);

setDefaultConfig(customConfig)

Click to expand

Allows you to globally override the default configuration for all requests. This is useful for setting application-wide defaults like timeouts, headers, or retry policies.

import { setDefaultConfig } from 'fetchff';

// Set global defaults for all requests
setDefaultConfig({
  timeout: 10000, // 10 seconds for all requests
  headers: {
    Authorization: 'Bearer your-token',
  },
  retry: {
    retries: 2,
    delay: 1500,
  },
});

// All subsequent requests will use these defaults
const { data } = await fetchf('/api/data'); // Uses 10s timeout and retry config

Instance with many API endpoints

createApiFetcher(config)

Click to expand

It is a powerful factory function for creating API fetchers with advanced features. It provides a convenient way to configure and manage multiple API endpoints using a declarative approach. This function offers integration with retry mechanisms, error handling improvements, and all the other settings. Unlike traditional methods, createApiFetcher() allows you to set up and use API endpoints efficiently with minimal boilerplate code.

Example

import { createApiFetcher } from 'fetchff';

// Create some endpoints declaratively
const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    getUser: {
      url: '/user-details/:id/',
      method: 'GET',
      // Each endpoint accepts all settings declaratively
      retry: { retries: 3, delay: 2000 },
      timeout: 5000,
      cancellable: true,
    },
    // Define more endpoints as needed
  },
  // You can set all settings globally
  strategy: 'softFail', // no try/catch required in case of errors
});

// Make a GET request to http://example.com/api/user-details/2/?rating[]=1&rating[]=2
const { data, error } = await api.getUser({
  params: { rating: [1, 2] }, //  Passed arrays, objects etc. will be parsed automatically
  urlPathParams: { id: 2 }, // Replace :id with 2 in the URL
});

Multiple API Specific Settings

All the Request Settings can be directly used in the function as global settings for all endpoints. They can be also used within the endpoints property (on per-endpoint basis). The exposed endpoints property is as follows:

• endpoints: Type: EndpointsConfig<EndpointTypes> List of your endpoints. Each endpoint is an object that accepts all the Request Settings (see the Basic Settings below). The endpoints are required to be specified.

How It Works

The createApiFetcher() automatically creates and returns API methods based on the endpoints object provided. It also exposes some extra methods and properties that are useful to handle global config, dynamically add and remove endpoints etc.

api.yourEndpoint(requestConfig)

Where yourEndpoint is the name of your endpoint, the key from endpoints object passed to the createApiFetcher().

requestConfig (optional) object - To have more granular control over specific endpoints you can pass Request Config for particular endpoint. Check Basic Settings below for more information.

Returns: Response Object (see below).

api.request(endpointNameOrUrl, requestConfig)

The api.request() helper function is a versatile method provided for making API requests with customizable configurations. It allows you to perform HTTP requests to any endpoint defined in your API setup and provides a straightforward way to handle queries, path parameters, and request configurations dynamically.

Example

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  apiUrl: 'https://example.com/api',
  endpoints: {
    updateUser: {
      url: '/update-user/:id',
      method: 'POST',
    },
    // Define more endpoints as needed
  },
});

// Using api.request to make a POST request
const { data, error } = await api.request('updateUser', {
  body: {
    name: 'John Doe', // Data Payload
  },
  urlPathParams: {
    id: '123', // URL Path Param :id will be replaced with 123
  },
});

// Using api.request to make a GET request to an external API
const { data, error } = await api.request('https://example.com/api/user', {
  params: {
    name: 'John Smith', // Query Params
  },
});

api.config

You can access api.config property directly to modify global headers and other settings on the fly. This is a property, not a function.

api.endpoints

You can access api.endpoints property directly to modify the endpoints list. This can be useful if you want to append or remove global endpoints. This is a property, not a function.

Advanced Utilities

Click to expand

Cache Management

mutate(key, newData, settings)

Programmatically update cached data without making a network request. Useful for optimistic updates or reflecting changes from other operations.

Parameters:

• key (string): The cache key to update
• newData (any): The new data to store in cache
• settings (object, optional): Configuration options
  • revalidate (boolean): Whether to trigger background revalidation after update

import { mutate } from 'fetchff';

// Update cache for a specific cache key
await mutate('/api/users', newUserData);

// Update with options
await mutate('/api/users', updatedData, {
  revalidate: true, // Trigger background revalidation
});

getCache(key)

Directly retrieve cached data for a specific cache key. Useful for reading the current cached response without triggering a network request.

Parameters:

• key (string): The cache key to retrieve (equivalent to cacheKey from request config or config.cacheKey from response object)

Returns: The cached response object, or null if not found

import { getCache } from 'fetchff';

// Get cached data for a specific key assuming you set {cacheKey: ''/api/user-profile'} in config
const cachedResponse = getCache('/api/user-profile');
if (cachedResponse) {
  console.log('Cached user profile:', cachedResponse.data);
}

setCache(key, response, ttl, staleTime)

Directly set cache data for a specific key. Unlike mutate(), this doesn't trigger revalidation by default. This is a low level function to directly set cache data based on particular key. If unsure, use the mutate() with revalidate: false instead.

Parameters:

• key (string): The cache key to set. It must match the cache key of the request.
• response (any): The full response object to store in cache
• ttl (number, optional): Time to live for the cache entry, in seconds. Determines how long the cached data remains valid before expiring. If not specified, the default 0 value will be used (discard cache immediately), if -1 specified then the cache will be held until manually removed using deleteCache(key) function.
• staleTime (number, optional): Duration, in seconds, for which cached data is considered "fresh" before it becomes eligible for background revalidation. If not specified, the default stale time applies.

import { setCache } from 'fetchff';

// Set cache data with custom ttl and staleTime
setCache('/api/user-profile', userData, 600, 60); // Cache for 10 minutes, fresh for 1 minute

// Set cache for specific endpoint infinitely
setCache('/api/user-settings', userSettings, -1);

deleteCache(key)

Remove cached data for a specific cache key. Useful for cache invalidation when you know data is stale.

Parameters:

• key (string): The cache key to delete

import { deleteCache } from 'fetchff';

// Delete specific cache entry
deleteCache('/api/user-profile');

// Delete cache after user logout
const logout = () => {
  deleteCache('/api/user/*'); // Delete all user-related cache
};

Revalidation Management

revalidate(key, isStaleRevalidation)

Manually trigger revalidation for a specific cache entry, forcing a fresh network request to update the cached data.

Parameters:

• key (string): The cache key to revalidate
• isStaleRevalidation (boolean, optional): Whether this is a background revalidation that doesn't mark as in-flight

import { revalidate } from 'fetchff';

// Revalidate specific cache entry
await revalidate('/api/user-profile');

// Revalidate with custom cache key
await revalidate('custom-cache-key');

// Background revalidation (doesn't mark as in-flight)
await revalidate('/api/user-profile', true);

revalidateAll(type, isStaleRevalidation)

Trigger revalidation for all cache entries associated with a specific event type (focus or online).

Parameters:

• type (string): The revalidation event type ('focus' or 'online')
• isStaleRevalidation (boolean, optional): Whether this is a background revalidation

import { revalidateAll } from 'fetchff';

// Manually trigger focus revalidation for all relevant entries
revalidateAll('focus');

// Manually trigger online revalidation for all relevant entries
revalidateAll('online');

removeRevalidators(type)

Clean up revalidation event listeners for a specific event type. Useful for preventing memory leaks when you no longer need automatic revalidation.

Parameters:

• type (string): The revalidation event type to remove ('focus' or 'online')

import { removeRevalidators } from 'fetchff';

// Remove all focus revalidation listeners
removeRevalidators('focus');

// Remove all online revalidation listeners
removeRevalidators('online');

// Typically called during cleanup
// e.g., in React useEffect cleanup or when unmounting components

Pub/Sub System

subscribe(key, callback)

Subscribe to cache updates and data changes. Receive notifications when specific cache entries are updated.

Parameters:

• key (string): The cache key to subscribe to
• callback (function): Function called when cache is updated
  • response (any): The full response object

Returns: Function to unsubscribe from updates

import { subscribe } from 'fetchff';

// Subscribe to cache changes for a specific key
const unsubscribe = subscribe('/api/user-data', (response) => {
  console.log('Cache updated with response:', response);
  console.log('Response data:', response.data);
  console.log('Response status:', response.status);
});

// Clean up subscription when no longer needed
unsubscribe();

Request Management

abortRequest(key, error)

Programmatically abort in-flight requests for a specific cache key or URL pattern.

Parameters:

• key (string): The cache key or URL pattern to abort
• error (Error, optional): Custom error to throw for aborted requests

import { abortRequest } from 'fetchff';

// Abort specific request by cache key
abortRequest('/api/slow-operation');

// Useful for cleanup when component unmounts or route changes
const cleanup = () => {
  abortRequest('/api/user-dashboard');
};

Network Detection

isSlowConnection()

Check if the user is on a slow network connection (2G/3G). Useful for adapting application behavior based on connection speed.

Parameters: None

Returns: Boolean indicating if connection is slow

import { isSlowConnection } from 'fetchff';

// Check connection speed and adapt behavior
if (isSlowConnection()) {
  console.log('User is on a slow connection');
  // Reduce image quality, disable auto-refresh, etc.
}

// Use in conditional logic
const shouldAutoRefresh = !isSlowConnection();
const imageQuality = isSlowConnection() ? 'low' : 'high';

🛠️ Plugin API Architecture

Click to expand

⚙️ Basic Settings

Click to expand

You can pass the settings:

• globally for all requests when calling createApiFetcher()
• per-endpoint basis defined under endpoints in global config when calling createApiFetcher()
• per-request basis when calling fetchf() (second argument of the function) or in the api.yourEndpoint() (third argument)

You can also use all native fetch() settings.

	Type	Default	Description
baseURL (alias: apiUrl)	string	undefined	Your API base url.
url	string	undefined	URL path e.g. /user-details/get
method	string	'GET'	Default request method e.g. GET, POST, DELETE, PUT etc. All methods are supported.
params	object URLSearchParams NameValuePair[]	undefined	Query Parameters - a key-value pairs added to the URL to send extra information with a request. If you pass an object, it will be automatically converted. It works with nested objects, arrays and custom data structures similarly to what jQuery used to do in the past. If you use createApiFetcher() then it is the first argument of your api.yourEndpoint() function. You can still pass configuration in 3rd argument if want to. You can pass key-value pairs where the values can be strings, numbers, or arrays. For example, if you pass { foo: [1, 2] }, it will be automatically serialized into foo[]=1&foo[]=2 in the URL.
body (alias: data)	object string FormData URLSearchParams Blob ArrayBuffer ReadableStream	undefined	The body is the data sent with the request, such as JSON, text, or form data, included in the request payload for POST, PUT, or PATCH requests.
urlPathParams	object	undefined	It lets you dynamically replace segments of your URL with specific values in a clear and declarative manner. This feature is especially handy for constructing URLs with variable components or identifiers. For example, suppose you need to update user details and have a URL template like /user-details/update/:userId. With urlPathParams, you can replace :userId with a real user ID, such as 123, resulting in the URL /user-details/update/123.
flattenResponse	boolean	false	When set to true, this option flattens the nested response data. This means you can access the data directly without having to use response.data.data. It works only if the response structure includes a single data property.
select	(data: any) => any	undefined	Function to transform or select a subset of the response data before it is returned. Called with the raw response data and should return the transformed data. Useful for mapping, picking, or shaping the response.
defaultResponse	any	null	Default response when there is no data or when endpoint fails depending on the chosen strategy
withCredentials	boolean	false	Indicates whether credentials (such as cookies) should be included with the request. This equals to credentials: "include" in native fetch(). In Node.js, cookies are not managed automatically. Use a fetch polyfill or library that supports cookies if needed.
timeout	number	30000 / 60000	You can set a request timeout in milliseconds. Default is adaptive: 30 seconds (30000 ms) for normal connections, 60 seconds (60000 ms) on slow connections (2G/3G). The timeout option applies to each individual request attempt including retries and polling. 0 means that the timeout is disabled.
dedupeTime	number	0	Time window, in milliseconds, during which identical requests are deduplicated (treated as single request). If set to 0, deduplication is disabled.
cacheTime	number	undefined	Specifies the duration, in seconds, for which a cache entry is considered "fresh." Once this time has passed, the entry is considered stale and may be refreshed with a new request. Set to -1 for indefinite cache. By default no caching.
staleTime	number	undefined	Specifies the duration, in seconds, for which cached data is considered "fresh." During this period, cached data will be returned immediately, but a background revalidation (network request) will be triggered to update the cache. If set to 0, background revalidation is disabled and revalidation is triggered on every access.
refetchOnFocus	boolean	false	When set to true, automatically revalidates (refetches) data when the browser window regains focus. Note: This bypasses the cache and always makes a fresh network request to ensure users see the most up-to-date data when they return to your application from another tab or window. Particularly useful for applications that display real-time or frequently changing data, but should be used judiciously to avoid unnecessary network traffic.
refetchOnReconnect	boolean	false	When set to true, automatically revalidates (refetches) data when the browser regains internet connectivity after being offline. This uses background revalidation to silently update data without showing loading states to users. Helps ensure your application displays fresh data after network interruptions. Works by listening to the browser's online event.
logger	Logger	null	You can additionally specify logger object with your custom logger to automatically log the errors to the console. It should contain at least error and warn functions.
fetcher	CustomFetcher	undefined	A custom fetcher async function. By default, the native fetch() is used. If you use your own fetcher, default response parsing e.g. await response.json() call will be skipped. Your fetcher should return response object / data directly.

📋 Additional Settings Available:
The table above shows the most commonly used settings. Many more advanced configuration options are available and documented in their respective sections below, including:

• 🔄 Retry Mechanism - retries, delay, maxDelay, backoff, resetTimeout, retryOn, shouldRetry
• 📶 Polling Configuration - pollingInterval, pollingDelay, maxPollingAttempts, shouldStopPolling
• 🗄️ Cache Management - cacheKey, cacheBuster, skipCache, cacheErrors
• ✋ Request Cancellation - cancellable, rejectCancelled
• 🌀 Interceptors - onRequest, onResponse, onError, onRetry
• 🔍 Error Handling - strategy

Performance Implications of Settings

Understanding the performance impact of different settings helps you optimize for your specific use case:

High-Performance Settings

Minimize Network Requests:

// Aggressive caching for static data
const staticConfig = {
  cacheTime: 3600, // 1 hour cache
  staleTime: 1800, // 30 minutes freshness
  dedupeTime: 10000, // 10 seconds deduplication
};

// Result: 90%+ reduction in network requests

Optimize for Mobile/Slow Connections:

const mobileOptimized = {
  timeout: 60000, // Longer timeout for slow connections (auto-adaptive)
  retry: {
    retries: 5, // More retries for unreliable connections
    delay: 2000, // Longer initial delay (auto-adaptive)
    backoff: 2.0, // Aggressive backoff
  },
  cacheTime: 900, // Longer cache on mobile
};

Memory vs Network Trade-offs

Memory-Efficient (Low Cache):

const memoryEfficient = {
  cacheTime: 60, // Short cache (1 minute)
  staleTime: undefined, // No stale-while-revalidate
  dedupeTime: 1000, // Short deduplication
};
// Pros: Low memory usage
// Cons: More network requests, slower perceived performance

Network-Efficient (High Cache):

const networkEfficient = {
  cacheTime: 1800, // Long cache (30 minutes)
  staleTime: 300, // 5 minutes stale-while-revalidate
  dedupeTime: 5000, // Longer deduplication
};
// Pros: Fewer network requests, faster user experience
// Cons: Higher memory usage, potentially stale data

Feature Performance Impact

Feature	Performance Impact	Best Use Case
Caching	⬇️ 70-90% fewer requests	Static or semi-static data
Deduplication	⬇️ 50-80% fewer concurrent requests	High-traffic applications
Stale-while-revalidate	⬆️ 90% faster perceived loading	Dynamic data that tolerates brief staleness
Request cancellation	⬇️ Reduced bandwidth waste	Search-as-you-type, rapid navigation
Retry mechanism	⬆️ 95%+ success rate	Mission-critical operations
Polling	⬆️ Real-time updates	Live data monitoring

Adaptive Performance by Connection

FetchFF automatically adapts timeouts and retry delays based on connection speed:

// Automatic adaptation (no configuration needed)
const adaptiveRequest = fetchf('/api/data');

// On fast connections (WiFi/4G):
// - timeout: 30 seconds
// - retry delay: 1 second → 1.5s → 2.25s...
// - max retry delay: 30 seconds

// On slow connections (2G/3G):
// - timeout: 60 seconds
// - retry delay: 2 seconds → 3s → 4.5s...
// - max retry delay: 60 seconds

Performance Patterns

Progressive Loading (Best UX):

// Layer 1: Instant response with cache
const quickData = await fetchf('/api/summary', {
  cacheTime: 300,
  staleTime: 60,
});

// Layer 2: Background enhancement
fetchf('/api/detailed-data', {
  strategy: 'silent',
  cacheTime: 600,
  onResponse(response) {
    updateUIWithDetailedData(response.data);
  },
});

Bandwidth-Conscious Loading:

// Check connection before expensive operations
import { isSlowConnection } from 'fetchff';

const loadUserDashboard = async () => {
  const isSlowConn = isSlowConnection();

  // Essential data always loads
  const userData = await fetchf('/api/user', {
    cacheTime: isSlowConn ? 600 : 300, // Longer cache on slow connections
  });

  // Optional data only on fast connections
  if (!isSlowConn) {
    fetchf('/api/user/analytics', { strategy: 'silent' });
    fetchf('/api/user/recommendations', { strategy: 'silent' });
  }
};

Performance Monitoring

Track key metrics to optimize your settings:

const performanceConfig = {
  onRequest(config) {
    console.time(`request-${config.url}`);
  },

  onResponse(response) {
    console.timeEnd(`request-${response.config.url}`);

    // Track cache hit rate
    if (response.fromCache) {
      incrementMetric('cache.hits');
    } else {
      incrementMetric('cache.misses');
    }
  },

  onError(error) {
    incrementMetric('requests.failed');
    console.warn('Request failed:', error.config.url, error.status);
  },
};

ℹ️ Note: This is just an example. You need to implement the incrementMetric function yourself to record or report performance metrics as needed in your application.

🏷️ Headers

Click to expand

fetchff provides robust support for handling HTTP headers in your requests. You can configure and manipulate headers at both global and per-request levels. Here’s a detailed overview of how to work with headers using fetchff.

Note: Header keys are case-sensitive when specified in request objects. Ensure that the keys are provided in the correct case to avoid issues with header handling.

Setting Headers Globally

You can set default headers that will be included in all requests made with a specific createApiFetcher instance. This is useful for setting common headers like authentication tokens or content types.

Example: Setting Headers Globally

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://api.example.com/',
  headers: {
    'Content-Type': 'application/json',
    Authorization: 'Bearer YOUR_TOKEN',
  },
  // other configurations
});

Setting Per-Request Headers

In addition to global default headers, you can also specify headers on a per-request basis. This allows you to override global headers or set specific headers for individual requests.

Example: Setting Per-Request Headers

import { fetchf } from 'fetchff';

// Example of making a GET request with custom headers
const { data } = await fetchf('https://api.example.com/endpoint', {
  headers: {
    Authorization: 'Bearer YOUR_ACCESS_TOKEN',
    'Custom-Header': 'CustomValue',
  },
});

Default Headers

The fetchff plugin automatically injects a set of default headers into every request. These default headers help ensure that requests are consistent and include necessary information for the server to process them correctly.

• Accept: application/json, text/plain, */* Indicates the media types that the client is willing to receive from the server. This includes JSON, plain text, and any other types.

• Accept-Encoding: gzip, deflate, br Specifies the content encoding that the client can understand, including gzip, deflate, and Brotli compression.

⚠️ Accept-Encoding in Node.js:
In Node.js, decompression is handled by the fetch implementation, and users should ensure their environment supports the encodings.

• Content-Type:
  Set automatically based on the request body type:

  • For JSON-serializable bodies (objects, arrays, etc.):
    application/json; charset=utf-8
  • For URLSearchParams:
    application/x-www-form-urlencoded
  • For ArrayBuffer/typed arrays:
    application/octet-stream
  • For FormData, Blob, File, or ReadableStream:
    Not set as the header is handled automatically by the browser and by Node.js 18+ native fetch.

  The Content-Type header is never overridden if you set it manually.

Summary:
You only need to set headers manually if you want to override these defaults. Otherwise, fetchff will handle the correct headers for most use cases, including advanced scenarios like file uploads, form submissions, and binary data.

🌀 Interceptors

Click to expand

Interceptor functions can be provided to customize the behavior of requests and responses. These functions are invoked at different stages of the request lifecycle and allow for flexible handling of requests, responses, and errors.

Example

const { data } = await fetchf('https://api.example.com/', {
  onRequest(config) {
    // Add a custom header before sending the request
    config.headers['Authorization'] = 'Bearer your-token';
  },
  onResponse(response) {
    // Log the response status
    console.log(`Response Status: ${response.status}`);
  },
  onError(error, config) {
    // Handle errors and log the request config
    console.error('Request failed:', error);
    console.error('Request config:', config);
  },
  onRetry(response, attempt) {
    // Log retry attempts for monitoring and debugging
    console.warn(
      `Retrying request (attempt ${attempt + 1}):`,
      response.config.url,
    );

    // Modify config for the upcoming retry request
    response.config.headers['Authorization'] = 'Bearer your-new-token';

    // Log error details for failed attempts
    if (response.error) {
      console.warn(
        `Retry reason: ${response.error.status} - ${response.error.statusText}`,
      );
    }

    // You can implement custom retry logic or monitoring here
    // For example, send retry metrics to your analytics service
  },
  retry: {
    retries: 3,
    delay: 1000,
    backoff: 1.5,
  },
});

Configuration

The following options are available for configuring interceptors in the fetchff settings:

• onRequest(config) => config:
  Type: RequestInterceptor | RequestInterceptor[]
  A function or an array of functions that are invoked before sending a request. Each function receives the request configuration object as its argument, allowing you to modify request parameters, headers, or other settings. Default: undefined (no modification).

• onResponse(response) => response:
  Type: ResponseInterceptor | ResponseInterceptor[]
  A function or an array of functions that are invoked when a response is received. Each function receives the full response object, enabling you to process the response, handle status codes, or parse data as needed.
  Default: undefined (no modification).

• onError(error) => error:
  Type: ErrorInterceptor | ErrorInterceptor[]
  A function or an array of functions that handle errors when a request fails. Each function receives the error and request configuration as arguments, allowing you to implement custom error handling logic or logging.
  Default: undefined (no modification).

• onRetry(response, attempt) => response:
  Type: RetryInterceptor | RetryInterceptor[]
  A function or an array of functions that are invoked before each retry attempt. Each function receives the response object (containing error information) and the current attempt number as arguments, allowing you to implement custom retry logging, monitoring, or conditional retry logic.
  Default: undefined (no retry interception).

All interceptors are asynchronous and can modify the provided config or response objects. You don't have to return a value, but if you do, any returned properties will be merged into the original argument.

Interceptor Execution Order

fetchff follows specific execution patterns for interceptor chains:

Request Interceptors: FIFO (First In, First Out)

Request interceptors execute in the order they are defined - from global to specific:

// Execution order: 1 → 2 → 3 → 4
const api = createApiFetcher({
  onRequest: (config) => {
    /* 1. Global interceptor */
  },
  endpoints: {
    getData: {
      onRequest: (config) => {
        /* 2. Endpoint interceptor */
      },
    },
  },
});

await api.getData({
  onRequest: (config) => {
    /* 3. Request interceptor */
  },
});

Response Interceptors: LIFO (Last In, First Out)

Response interceptors execute in reverse order - from specific to global:

// Execution order: 3 → 2 → 1
const api = createApiFetcher({
  onResponse: (response) => {
    /* 3. Global interceptor (executes last) */
  },
  endpoints: {
    getData: {
      onResponse: (response) => {
        /* 2. Endpoint interceptor */
      },
    },
  },
});

await api.getData({
  onResponse: (response) => {
    /* 1. Request interceptor (executes first) */
  },
});

This pattern ensures that:

• Request interceptors can progressively enhance configuration from general to specific
• Response interceptors can process data from specific to general, allowing request-level interceptors to handle the response first before global cleanup or logging

How It Works

1. Request Interception:
   Before a request is sent, the onRequest interceptors are invoked. These interceptors can modify the request configuration, such as adding headers or changing request parameters.

2. Response Interception:
   Once a response is received, the onResponse interceptors are called. These interceptors allow you to handle the response data, process status codes, or transform the response before it is returned to the caller.

3. Error Interception:
   If a request fails and an error occurs, the onError interceptors are triggered. These interceptors provide a way to handle errors, such as logging or retrying requests, based on the error and the request configuration.

4. Custom Handling:
   Each interceptor function provides a flexible way to customize request and response behavior. You can use these functions to integrate with other systems, handle specific cases, or modify requests and responses as needed.

🌐 Network Revalidation

Click to expand

fetchff provides intelligent network revalidation features that automatically keep your data fresh based on user interactions and network connectivity. These features help ensure users always see up-to-date information without manual intervention.

Focus Revalidation

When refetchOnFocus is enabled, requests are automatically triggered when the browser window regains focus (e.g., when users switch back to your tab).

const { data } = await fetchf('/api/user-profile', {
  refetchOnFocus: true, // Revalidate when window gains focus
  cacheTime: 300, // Cache for 5 minutes, but still revalidate on focus
});

Network Reconnection Revalidation

The refetchOnReconnect feature automatically revalidates data when the browser detects that internet connectivity has been restored after being offline.

const { data } = await fetchf('/api/notifications', {
  refetchOnReconnect: true, // Revalidate when network reconnects
  cacheTime: 600, // Cache for 10 minutes, but revalidate when back online
});

Adaptive Timeouts

fetchff automatically adjusts request timeouts based on connection speed to provide optimal user experience:

// Automatically uses:
// - 30 seconds timeout on normal connections
// - 60 seconds timeout on slow connections (2G/3G)
const { data } = await fetchf('/api/data');

// You can still override with custom timeout
const { data: customTimeout } = await fetchf('/api/data', {
  timeout: 10000, // Force 10 seconds regardless of connection speed
});

// Check connection speed manually
import { isSlowConnection } from 'fetchff';

if (isSlowConnection()) {
  console.log('User is on a slow connection');
  // Adjust your app behavior accordingly
}

How It Works

1. Event Listeners: fetchff automatically attaches global event listeners for focus and online events when needed
2. Background Revalidation: Network revalidation uses background requests that don't show loading states to users
3. Automatic Cleanup: Event listeners are properly managed and cleaned up to prevent memory leaks
4. Smart Caching: Revalidation works alongside caching - fresh data updates the cache for future requests
5. Stale-While-Revalidate: Use staleTime to control when background revalidation happens automatically
6. Connection Awareness: Automatically detects connection speed and adjusts timeouts for better reliability

Configuration Options

Both revalidation features can be configured globally or per-request, and work seamlessly with cache timing:

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://api.example.com',
  // Global settings apply to all endpoints
  refetchOnFocus: true,
  refetchOnReconnect: true,
  cacheTime: 300, // Cache for 5 minutes
  staleTime: 60, // Consider fresh for 1 minute, then background revalidate
  endpoints: {
    getCriticalData: {
      url: '/critical-data',
      // Override global settings for specific endpoints
      refetchOnFocus: true,
      refetchOnReconnect: true,
      staleTime: 30, // More aggressive background revalidation for critical data
    },
    getStaticData: {
      url: '/static-data',
      // Disable revalidation for static data
      refetchOnFocus: false,
      refetchOnReconnect: false,
      staleTime: 3600, // Background revalidate after 1 hour
    },
  },
});

Use Cases

Focus Revalidation is ideal for:

• Real-time dashboards and analytics
• Social media feeds and chat applications
• Financial data and trading platforms
• Any data that changes frequently while users are away

Reconnection Revalidation is perfect for:

• Mobile applications with intermittent connectivity
• Offline-capable applications
• Critical data that must be current when online
• Applications used in areas with unstable internet

Best Practices

1. Combine with appropriate cache and stale times:

   const { data } = await fetchf('/api/live-data', {
     cacheTime: 300, // Cache for 5 minutes
     staleTime: 30, // Consider fresh for 30 seconds
     refetchOnFocus: true, // Also revalidate on focus
     refetchOnReconnect: true,
   });

2. Use staleTime for automatic background updates - Data stays fresh without user interaction:

   // Good: Automatic background revalidation for dynamic data
   const { data: notifications } = await fetchf('/api/notifications', {
     cacheTime: 600, // Cache for 10 minutes
     staleTime: 60, // Background revalidate after 1 minute
     refetchOnFocus: true,
   });
   
   // Good: Less frequent updates for semi-static data
   const { data: userProfile } = await fetchf('/api/profile', {
     cacheTime: 1800, // Cache for 30 minutes
     staleTime: 600, // Background revalidate after 10 minutes
     refetchOnReconnect: true,
   });

3. Use selectively - Don't enable for all requests to avoid unnecessary network traffic:

   // Good: Enable for critical, changing data
   const { data: userNotifications } = await fetchf('/api/notifications', {
     refetchOnFocus: true,
     refetchOnReconnect: true,
   });
   
   // Avoid: Don't enable for static configuration data
   const { data: appConfig } = await fetchf('/api/config', {
     cacheTime: 3600, // Cache for 1 hour
     staleTime: 0, // Disable background revalidation
     refetchOnFocus: false,
     refetchOnReconnect: false,
   });

4. Consider user experience - Network revalidation happens silently in the background, providing smooth UX without loading spinners.

⚠️ Browser Support: These features work in all modern browsers that support the focus and online events. In server-side environments (Node.js), these options are safely ignored.

🗄️ Cache Management

Click to expand

The caching mechanism in fetchf() and createApiFetcher() enhances performance by reducing redundant network requests and reusing previously fetched data when appropriate. This system ensures that cached responses are managed efficiently and only used when considered "fresh". Below is a breakdown of the key parameters that control caching behavior and their default values.

⚠️ When using in Node.js:
Cache and deduplication are in-memory and per-process. For distributed or serverless environments, consider external caching if persistence is needed.

Example

const { data } = await fetchf('https://api.example.com/', {
  cacheTime: 300, // Cache is valid for 5 minutes, set -1 for indefinite cache. By default no cache.
  cacheKey: (config) => `${config.url}-${config.method}`, // Custom cache key based on URL and method, default automatically generated
  cacheBuster: (config) => config.method === 'POST', // Bust cache for POST requests, by default no busting.
  skipCache: (response, config) => response.status !== 200, // Skip caching on non-200 responses, by default no skipping
  cacheErrors: false, // Cache error responses as well as successful ones, default false
  staleTime: 600, // Data is considered fresh for 10 minutes before background revalidation (0 by default, meaning no background revalidation)
});

Configuration

The caching system can be fine-tuned using the following options when configuring the:

• cacheTime:
  Type: number
  Specifies the duration, in seconds, for which a cache entry is considered "fresh." Once this time has passed, the entry is considered stale and may be refreshed with a new request. Set to -1 for indefinite cache. Default: undefined (no caching).

• cacheKey:
  Type: CacheKeyFunction | string
  A string or function used to generate a custom cache key for the request cache, deduplication etc. If not provided, a default key is created by hashing various parts of the request, including Method, URL, query parameters, and headers etc. Providing string can help to greatly improve the performance of the requests, avoid unnecessary request flooding etc.

  You can provide either:

  • A string: Used directly as the cache key for all requests using matching string.
  • A function: Receives the full request config as an argument and should return a unique string key. This allows you to include any relevant part of the request (such as URL, method, params, body, or custom logic) in the cache key.

  Example:

  cacheKey: (config) =>
    `${config.method}:${config.url}:${JSON.stringify(config.params)}`;

  This flexibility ensures you can control cache granularity—whether you want to cache per endpoint, per user, or based on any other criteria.

  Default: Auto-generated based on request properties (see below).

• cacheBuster:
  Type: CacheBusterFunction
  A function that allows you to invalidate or refresh the cache under certain conditions, such as specific request methods or response properties. This is useful for ensuring that certain requests (e.g., POST) bypass the cache.
  Default: (config) => false (no cache busting).

• skipCache:
  Type: CacheSkipFunction
  A function that determines whether caching should be skipped based on the response. This allows for fine-grained control over whether certain responses are cached or not, such as skipping non-200 responses.
  Default: (response, config) => false (no skipping).

• cacheErrors:
  Type: boolean
  Determines whether error responses (such as HTTP 4xx or 5xx) should also be cached. If set to true, both successful and error responses are stored in the cache. If false, only successful responses are cached.
  Default: false.

• staleTime:
  Specifies the time in seconds during which cached data is considered "fresh" before it becomes stale and triggers background revalidation (SWR: stale-while-revalidate).

  • Set to a number greater than 0 to enable SWR: cached data will be served instantly, and a background request will update the cache after this period.
  • Set to 0 to treat data as stale immediately (always eligible for refetch).
  • Set to undefined to disable SWR: data is never considered stale and background revalidation is not performed.
    Default: undefined to disable SWR pattern (data is never considered stale) or 300 (5 minutes) in libraries like React.

  How It Works

  1. Cache Lookup:
     When a request is made, fetchff first checks the internal cache for a matching entry using the generated cache key. If a valid and "fresh" cache entry exists (within cacheTime), the cached response is returned immediately. If the native fetch() option cache: 'reload' is set, the internal cache is bypassed and a fresh request is made.

  2. Cache Key Generation:
     Each request is uniquely identified by a cache key, which is auto-generated from the URL, method, params, headers, and other relevant options. You can override this by providing a custom cacheKey string or function for fine-grained cache control.

  3. Cache Busting:
     If a cacheBuster function is provided, it determines whether to invalidate (bust) the cache for a given request. This is useful for scenarios like forcing fresh data on POST requests or after certain actions.

  4. Conditional Caching:
     The skipCache function allows you to decide, per response, whether it should be stored in the cache. For example, you can skip caching for error responses (like HTTP 4xx/5xx) or based on custom logic.

  5. Network Request and Cache Update:
     If no valid cache entry is found, or if caching is skipped or busted, the request is sent to the network. The response is then cached according to your configuration, making it available for future requests.

🔄 Cache and Deduplication Integration

Understanding how caching works together with request deduplication is crucial for optimal performance:

Cache-First, Then Deduplication

// Multiple components requesting the same data
const userProfile1 = useFetcher('/api/user/123', { cacheTime: 300 });
const userProfile2 = useFetcher('/api/user/123', { cacheTime: 300 });
const userProfile3 = useFetcher('/api/user/123', { cacheTime: 300 });

// Flow:
// 1. First request checks cache → cache miss → network request initiated
// 2. Second request checks cache → cache miss → joins in-flight request (deduplication)
// 3. Third request checks cache → cache miss → joins in-flight request (deduplication)
// 4. When network response arrives → cache is populated → all requests receive same data

Cache Hit Scenarios

// First request (cache miss - goes to network)
const request1 = fetchf('/api/data', { cacheTime: 300, dedupeTime: 5000 });

// After 2 seconds - cache hit (no deduplication needed)
setTimeout(() => {
  const request2 = fetchf('/api/data', { cacheTime: 300, dedupeTime: 5000 });
  // Returns cached data immediately, no network request
}, 2000);

// After 10 minutes - cache expired, new request
setTimeout(() => {
  const request3 = fetchf('/api/data', { cacheTime: 300, dedupeTime: 5000 });
  // Cache expired → new network request → potential for deduplication again
}, 600000);

Deduplication Window vs Cache Time

• dedupeTime: Prevents duplicate requests during a short time window (milliseconds)
• cacheTime: Stores successful responses for longer periods (seconds)
• Integration: Deduplication handles concurrent requests, caching handles subsequent requests

const config = {
  dedupeTime: 2000, // 2 seconds - for rapid concurrent requests
  cacheTime: 300, // 5 minutes - for longer-term storage
};

// Timeline example:
// T+0ms:   Request A initiated → network call starts
// T+500ms: Request B initiated → joins Request A (deduplication)
// T+1500ms: Request C initiated → joins Request A (deduplication)
// T+2500ms: Request D initiated → deduplication window expired, but cache hit!
// T+6000ms: Request E initiated → cache hit (no network call needed)

⏰ Understanding staleTime vs cacheTime

The relationship between staleTime and cacheTime enables sophisticated data freshness strategies:

Cache States and Timing

const fetchWithTimings = fetchf('/api/user-feed', {
  cacheTime: 600, // Cache for 10 minutes
  staleTime: 60, // Consider fresh for 1 minute
});

// Data lifecycle:
// T+0:     Fresh data - served from cache, no background request
// T+30s:   Still fresh - served from cache, no background request
// T+90s:   Stale but cached - served from cache + background revalidation
// T+300s:  Still stale - served from cache + background revalidation
// T+650s:  Cache expired - network request required, shows loading state

Practical Combinations

High-Frequency Updates (Real-time Data)

const realtimeData = {
  cacheTime: 30, // Cache for 30 seconds
  staleTime: 5, // Fresh for 5 seconds only
  // Result: Frequent background updates, always responsive UI
};

Balanced Performance (User Data)

const userData = {
  cacheTime: 300, // Cache for 5 minutes
  staleTime: 60, // Fresh for 1 minute
  // Result: Good performance + reasonable freshness
};

Static Content (Configuration)

const staticConfig = {
  cacheTime: 3600, // Cache for 1 hour
  staleTime: 1800, // Fresh for 30 minutes
  // Result: Minimal network usage for rarely changing data
};

Background Revalidation Behavior

// When staleTime expires but cacheTime hasn't:
const { data } = await fetchf('/api/notifications', {
  cacheTime: 600, // 10 minutes total cache
  staleTime: 120, // 2 minutes of "freshness"
});

// T+0:     Returns cached data immediately, no background request
// T+150s:  Returns cached data immediately + triggers background request
// T+150s:  Background request completes → cache silently updated
// T+650s:  Cache expired → full loading state + network request

Auto-Generated Cache Key Properties

By default, fetchff generates a cache key automatically using a combination of the following request properties:

Property	Description	Default Value
method	The HTTP method used for the request (e.g., GET, POST).	'GET'
url	The full request URL, including the base URL and endpoint path.	''
headers	Request headers, filtered to include only cache-relevant headers (see below).
body	The request payload (for POST, PUT, PATCH, etc.), stringified if it's an object or array.
credentials	Indicates whether credentials (cookies) are included in the request.	'same-origin'
params	Query parameters serialized into the URL (objects, arrays, etc. are stringified).
urlPathParams	Dynamic URL path parameters (e.g., /user/:id), stringified and encoded.
withCredentials	Whether credentials (cookies) are included in the request.

Header Filtering for Cache Keys

To ensure stable cache keys and prevent unnecessary cache misses, fetchff only includes headers that affect response content in cache key generation. The following headers are included:

Content Negotiation:

• accept - Affects response format (JSON, HTML, etc.)
• accept-language - Affects localization of response
• accept-encoding - Affects response compression

Authentication & Authorization:

• authorization - Affects access to protected resources
• x-api-key - Token-based access control
• cookie - Session-based authentication

Request Context:

• content-type - Affects how request body is interpreted
• origin - Relevant for CORS or tenant-specific APIs
• referer - May influence API behavior
• user-agent - Only if server returns client-specific content

Custom Headers:

• x-requested-with - Distinguishes AJAX requests
• x-client-id - Per-client/partner identity
• x-tenant-id - Multi-tenant segmentation
• x-user-id - Explicit user context
• x-app-version - Version-specific behavior
• x-feature-flag - Feature rollout controls
• x-device-id - Device-specific responses
• x-platform - Platform-specific content (iOS, Android, web)
• x-session-id - Session-specific responses
• x-locale - Locale-specific content

Headers like user-agent, accept-encoding, connection, cache-control, tracking IDs, and proxy-related headers are excluded from cache key generation as they don't affect the actual response content.

These properties are combined and hashed to create a unique cache key for each request. This ensures that requests with different parameters, bodies, or cache-relevant headers are cached separately while maintaining stable cache keys across requests that only differ in non-essential headers. If that does not suffice, you can always use cacheKey (string | function) and supply it to particular requests. You can also build your own cacheKey function and simply update defaults to reflect it in all requests. Auto key generation would be entirely skipped in such scenarios.

🔁 Deduplication & In-Flight Requests

Click to expand

fetchff automatically deduplicates identical requests that are made within a configurable time window, ensuring that only one network request is sent for the same endpoint and parameters. This is especially useful for scenarios where multiple components or users might trigger the same request simultaneously (e.g., rapid user input, concurrent UI updates).

⚠️ When using in Node.js:
Request queueing and deduplication are per-process. In multi-process or serverless environments, requests are not deduplicated across instances.

How Deduplication Works

• When a request is made, fetchff checks if an identical request (same URL, method, params, and body) is already in progress or was recently completed within the dedupeTime window.
• If such a request exists, the new request will "join" the in-flight request and receive the same response when it completes, rather than triggering a new network call.
• This mechanism reduces unnecessary network traffic and ensures consistent data across your application.

Configuration

• dedupeTime:
  • Type: number
  • Default: 0 (milliseconds)
  • Specifies the time window during which identical requests are deduplicated. If set to 0, deduplication is disabled.

Example

import { fetchf } from 'fetchff';

// Multiple rapid calls to the same endpoint will be deduplicated
fetchf('/api/search', { params: { q: 'test' }, dedupeTime: 2000 });
fetchf('/api/search', { params: { q: 'test' }, dedupeTime: 2000 });
// Only one network request will be sent within the 2-second window

Benefits

• Prevents duplicate network requests for the same resource.
• Reduces backend load and improves frontend performance.
• Ensures that all consumers receive the same response for identical requests made in quick succession.

This deduplication logic is applied both to standalone fetchf() calls and to endpoints created with createApiFetcher().

✋ Request Cancellation

Click to expand

fetchff simplifies making API requests by allowing customizable features such as request cancellation, retries, and response flattening. When a new request is made to the same API endpoint, the plugin automatically cancels any previous requests that haven't completed, ensuring that only the most recent request is processed.

It also supports:

• Automatic retries for failed requests with configurable delay and exponential backoff.
• Optional flattening of response data for easier access, removing nested data fields.

You can choose to reject cancelled requests or return a default response instead through the defaultResponse setting.

Example

import { fetchf } from 'fetchff';

// Function to send the request
const sendRequest = () => {
  // In this example, the previous requests are automatically cancelled
  // You can also control "dedupeTime" setting in order to fire the requests more or less frequently
  fetchf('https://example.com/api/messages/update', {
    method: 'POST',
    cancellable: true,
    rejectCancelled: true,
  });
};

// Attach keydown event listener to the input element with id "message"
document.getElementById('message')?.addEventListener('keydown', sendRequest);

Configuration

• cancellable: Type: boolean Default: false If set to true, any ongoing previous requests to the same API endpoint will be automatically cancelled when a subsequent request is made before the first one completes. This is useful in scenarios where repeated requests are made to the same endpoint (e.g., search inputs) and only the latest response is needed, avoiding unnecessary requests to the backend.

• rejectCancelled: Type: boolean Default: false Works in conjunction with the cancellable option. If set to true, the promise of a cancelled request will be rejected. By default (false), when a request is cancelled, instead of rejecting the promise, a defaultResponse will be returned, allowing graceful handling of cancellation without errors.

📶 Polling Configuration

Click to expand

Polling can be configured to repeatedly make requests at defined intervals until certain conditions are met. This allows for continuously checking the status of a resource or performing background updates.

Example

const { data } = await fetchf('https://api.example.com/', {
  pollingInterval: 5000, // Poll every 5 seconds (useful for regular polling at intervals)
  pollingDelay: 1000, // Wait 1 second before each polling attempt begins
  maxPollingAttempts: 10, // Stop polling after 10 attempts
  shouldStopPolling(response, attempt) {
    if (response && response.status === 200) {
      return true; // Stop polling if the response status is 200 (OK)
    }
    if (attempt >= 10) {
      return true; // Stop polling after 10 attempts
    }
    return false; // Continue polling otherwise
  },
});

Configuration

The following options are available for configuring polling in the RequestHandler:

• pollingInterval:
  Type: number
  Interval in milliseconds between polling attempts. If set to 0, polling is disabled. This allows you to control the frequency of requests when polling is enabled. It is useful for regular, periodic polling. Default: 0 (polling disabled).

• pollingDelay:
  Type: number
  The time (in milliseconds) to wait before each polling attempt begins. It is useful if you want to throttle or stagger requests, or wait a bit before each poll. It basically adds a delay before each poll is started (including the first one). Default: 0 (no delay).

• maxPollingAttempts:
  Type: number
  Maximum number of polling attempts before stopping. Set to 0 or negative number for unlimited attempts.
  Default: 0 (unlimited).

• shouldStopPolling:
  Type: (response: any, attempt: number) => boolean
  A function to determine if polling should stop based on the response, error, or the current polling attempt number (attempt starts with 1). Return true to stop polling, and false to continue polling. This allows for custom logic to decide when to stop polling based on the conditions of the response or error.
  Default: (response, attempt) => false (polling continues indefinitely unless manually stopped).

How It Works

1. Polling Interval:
   When pollingInterval is set to a non-zero value, polling begins after the initial request. The request is repeated at intervals defined by the pollingInterval setting.

2. Polling Delay:
   The pollingDelay setting introduces a delay before each polling attempt, allowing for finer control over the timing of requests.

3. Maximum Polling Attempts:
   The maxPollingAttempts setting limits the number of polling attempts. If the maximum number of attempts is reached, polling stops automatically.

4. Stopping Polling:
   The shouldStopPolling function is invoked after each polling attempt. If it returns true, polling will stop. Otherwise, polling will continue until the condition to stop is met, or polling is manually stopped.

5. Custom Logic:
   The shouldStopPolling function provides flexibility to implement custom logic based on the response, error, or the number of attempts. This makes it easy to stop polling when the desired outcome is reached or after a maximum number of attempts.

🔄 Retry Mechanism

Click to expand

The retry mechanism can be used to handle transient errors and improve the reliability of network requests. This mechanism automatically retries requests when certain conditions are met, providing robustness in the face of temporary failures. Below is an overview of how the retry mechanism works and how it can be configured.

Example

const { data } = await fetchf('https://api.example.com/', {
  retry: {
    retries: 5,
    delay: 100, // Override default adaptive delay (normally 1s/2s based on connection)
    maxDelay: 5000, // Override default adaptive maxDelay (normally 30s/60s based on connection)
    resetTimeout: true, // Resets the timeout for each retry attempt
    backoff: 1.5,
    retryOn: [500, 503],
    // Retry on specific errors or based on custom logic
    shouldRetry(response, attempt) {
      // Retry if the status text is Not Found (404)
      if (response.error && response.error.statusText === 'Not Found') {
        return true;
      }

      // Use `response.data` to access any data from fetch() response
      const data = response.data;

      // Let's say your backend returns bookId as "none". You can force retry by returning "true".
      if (data?.bookId === 'none') {
        return true;
      }

      return attempt < 3; // Retry up to 3 times.
    },
  },
});

In this example, the request will retry only on HTTP status codes 500 and 503, as specified in the retryOn array. The resetTimeout option ensures that the timeout is restarted for each retry attempt. The custom shouldRetry function adds further logic: if the server response contains {"bookId": "none"}, a retry is forced. Otherwise, the request will retry only if the current attempt number is less than 3. Although the retries option is set to 5, the shouldRetry function limits the maximum attempts to 3 (the initial request plus 2 retries).

Note: When not overridden, fetchff automatically adapts retry delays based on connection speed:

• Normal connections: 1s initial delay, 30s max delay
• Slow connections (2G/3G): 2s initial delay, 60s max delay

Additionally, you can handle "Not Found" (404) responses or other specific status codes in your retry logic. For example, you might want to retry when the status text is "Not Found":

shouldRetry(response, attempt) {
  // Retry if the status text is Not Found (404)
  if (response.error && response.error.statusText === 'Not Found') {
    return true;
  }
  // ...other logic

  return null; // Fallback to `retryOn` status code check
}

This allows you to customize retry behavior for cases where a resource might become available after a short delay, or when you want to handle transient 404 errors gracefully.

The whole Error object is under response.error generally.

Configuration

The retry mechanism is configured via the retry option when instantiating the RequestHandler. You can customize the following parameters:

• retries:
  Type: number
  Number of retry attempts to make after an initial failure.
  Default: 0 (no retries).

• delay:
  Type: number
  Initial delay (in milliseconds) before the first retry attempt. Default is adaptive: 1 second (1000 ms) for normal connections, 2 seconds (2000 ms) on slow connections (2G/3G). Subsequent retries use an exponentially increasing delay based on the backoff parameter.
  Default: 1000 / 2000 (adaptive based on connection speed).

• maxDelay:
  Type: number
  Maximum delay (in milliseconds) between retry attempts. Default is adaptive: 30 seconds (30000 ms) for normal connections, 60 seconds (60000 ms) on slow connections (2G/3G). The delay will not exceed this value, even if the exponential backoff would suggest a longer delay.
  Default: 30000 / 60000 (adaptive based on connection speed).

• backoff:
  Type: number
  Factor by which the delay is multiplied after each retry. For example, a backoff factor of 1.5 means each retry delay is 1.5 times the previous delay. It means that after the first failure, wait for x seconds. After the second failure, wait for x _ 1.5 seconds. After the third failure, wait for x _ 1.5^2 seconds, and so on. Default: 1.5.

• resetTimeout:
  Type: boolean
  If set to true, the timeout for the request is reset for each retry attempt. This ensures that the timeout applies to each individual retry rather than the entire request lifecycle.
  Default: true.

• retryOn:
  Type: number[]
  Array of HTTP status codes that should trigger a retry. By default, retries are triggered for the following status codes:

  • 408 - Request Timeout
  • 409 - Conflict
  • 425 - Too Early
  • 429 - Too Many Requests
  • 500 - Internal Server Error
  • 502 - Bad Gateway
  • 503 - Service Unavailable
  • 504 - Gateway Timeout

If used in conjunction with shouldRetry, the shouldRetry function takes priority, and falls back to retryOn only if it returns null.

• shouldRetry(response: FetchResponse, currentAttempt: Number) => boolean:
  Type: RetryFunction<ResponseData, RequestBody, QueryParams, PathParams>
  Function that determines whether a retry should be attempted based on the error or successful response (if shouldRetry is provided) object, and the current attempt number. This function receives the error object and the attempt number as arguments. The boolean returned indicates decision. If true then it should retry, if false then abort and don't retry, if null then fallback to retryOn status codes check. Default: undefined.

How It Works

1. Initial Request: When a request fails, the retry mechanism captures the failure and checks if it should retry based on the retryOn configuration and the result of the shouldRetry function.

2. Retry Attempts: If a retry is warranted:

   • The request is retried up to the specified number of attempts (retries).
   • Each retry waits for a delay before making the next attempt. The delay starts at the initial delay value and increases exponentially based on the backoff factor, but will not exceed the maxDelay.
   • If resetTimeout is enabled, the timeout is reset for each retry attempt.

3. Logging: During retries, the mechanism logs warnings indicating the retry attempts and the delay before the next attempt, which helps in debugging and understanding the retry behavior.

4. Final Outcome: If all retry attempts fail, the request will throw an error, and the final failure is processed according to the configured error handling logic.

429 Retry-After Handling

When a request receives a 429 Too Many Requests response, fetchff will automatically check for the Retry-After header and use its value to determine the delay before the next retry attempt. This works for both seconds and HTTP-date formats, and falls back to your configured delay if the header is missing or invalid.

How it works:

• If the server responds with 429 and a Retry-After header, the delay for the next retry will be set to the value from that header (in ms).
• If the header is missing or invalid, the default retry delay is used.

Example:

const { data } = await fetchf('https://api.example.com/', {
  retry: {
    retries: 2,
    delay: 1000, // fallback if Retry-After is missing
    retryOn: [429], // 429 is already checked by default so it is not necessary to add it
  },
});

If the server responds with:

HTTP/1.1 429 Too Many Requests
Retry-After: 5

The next retry will wait 5000ms before attempting again.

If the header is an HTTP-date, the delay will be calculated as the difference between the date and the current time.

🧩 Response Data Transformation

Click to expand

The fetchff plugin automatically handles response data transformation for any instance of Response returned by the fetch() (or a custom fetcher) based on the Content-Type header, ensuring that data is parsed correctly according to its format.

How It Works

• JSON (application/json): Parses the response as JSON.
• Form Data (multipart/form-data): Parses the response as FormData.
• Binary Data (application/octet-stream): Parses the response as a Blob.
• URL-encoded Form Data (application/x-www-form-urlencoded): Parses the response as FormData.
• Text (text/*): Parses the response as plain text.

If the Content-Type header is missing or not recognized, the plugin defaults to attempting JSON parsing. If that fails, it will try to parse the response as text.

This approach ensures that the fetchff plugin can handle a variety of response formats, providing a flexible and reliable method for processing data from API requests.

⚠️ When using in Node.js:
In Node.js, using FormData, Blob, or ReadableStream may require additional polyfills or will not work unless your fetch polyfill supports them.

onResponse Interceptor

You can use the onResponse interceptor to customize how the response is handled before it reaches your application. This interceptor gives you access to the raw Response object, allowing you to transform the data or modify the response behavior based on your needs.

📄 Response Object

Click to expand

Every request returns a standardized response object from native fetch() extended by a few handful properties:

Response Object Structure

interface FetchResponse<
  ResponseData = any,
  RequestBody = any,
  QueryParams = any,
  PathParams = any,
> extends Response {
  data: ResponseData | null; // The parsed response data, or null/defaultResponse if unavailable
  error: ResponseError<
    ResponseData,
    RequestBody,
    QueryParams,
    PathParams
  > | null; // Error details if the request failed, otherwise null
  config: RequestConfig; // The configuration used for the request
  status: number; // HTTP status code
  statusText: string; // HTTP status text
  headers: HeadersObject; // Response headers as a key-value object
}

• data:
  The actual data returned from the API, or null/defaultResponse if not available.

• error:
  An object containing error details if the request failed, or null otherwise. Includes properties such as name, message, status, statusText, request, config, and the full response.

• config:
  The complete configuration object used for the request, including URL, method, headers, and parameters.

• status:
  The HTTP status code of the response (e.g., 200, 404, 500).

• statusText:
  The HTTP status text (e.g., 'OK', 'Not Found', 'Internal Server Error').

• headers:
  The response headers as a plain key-value object.

The whole response of the native fetch() is attached as well.

Error object in error looks as follows:

• Type: ResponseError<ResponseData, RequestBody, QueryParams, PathParams> | null

• An object with details about any error that occurred or null otherwise.

• name: The name of the error, that is ResponseError.

• message: A descriptive message about the error.

• status: The HTTP status code of the response (e.g., 404, 500).

• statusText: The HTTP status text of the response (e.g., 'Not Found', 'Internal Server Error').

• request: Details about the HTTP request that was sent (e.g., URL, method, headers).

• config: The configuration object used for the request, including URL, method, headers, and query parameters.

• response: The full response object received from the server, including all headers and body.

• isCancelled: A boolean property on the error object indicating whether the request was cancelled before completion

🔍 Error Handling

Click to expand

Error handling strategies define how to manage errors that occur during requests. You can configure the strategy option to specify what should happen when an error occurs. This affects whether promises are rejected, if errors are handled silently, or if default responses are provided. You can also combine it with onError interceptor for more tailored approach.

The native fetch() API function doesn't throw exceptions for HTTP errors like 404 or 500 — it only rejects the promise if there is a network-level error (e.g. the request fails due to a DNS error, no internet connection, or CORS issues). The fetchf() function brings consistency and lets you align the behavior depending on chosen strategy. By default, all errors are rejected.

Configuration

strategy

reject: (default) Promises are rejected, and global error handling is triggered. You must use try/catch blocks to handle errors.

import { fetchf } from 'fetchff';

try {
  const { data } = await fetchf('https://api.example.com/users', {
    strategy: 'reject', // Default strategy - can be omitted
    timeout: 5000,
  });

  console.log('Users fetched successfully:', data);
} catch (error) {
  // Handle specific error types
  if (error.status === 404) {
    console.error('API endpoint not found');
  } else if (error.status >= 500) {
    console.error('Server error:', error.statusText);
  } else {
    console.error('Request failed:', error.message);
  }
}

softFail:
Returns a response object with additional property of error when an error occurs and does not throw any error. This approach helps you to handle error information directly within the response's error object without the need for try/catch blocks.

⚠️ Always Check the error Property:
When using the softFail or defaultResponse strategies, the promise will not throw on error. You must always check the error property in the response object to detect and handle errors.

import { fetchf } from 'fetchff';

const { data, error } = await fetchf('https://api.example.com/users', {
  strategy: 'softFail',
  timeout: 5000,
});

if (error) {
  // Handle errors without try/catch
  console.error('Request failed:', {
    status: error.status,
    message: error.message,
    url: error.config?.url,
  });

  // Show user-friendly error message
  if (error.status === 429) {
    console.log('Rate limited. Please try again later.');
  } else if (error.status >= 500) {
    console.log('Server temporarily unavailable. Please try again.');
  }
} else {
  console.log('Users fetched successfully:', data);
}

Check Response Object section below to see how error object is structured.

defaultResponse:
Returns a default response specified in case of an error. The promise will not be rejected. This can be used in conjunction with flattenResponse and defaultResponse: {} to provide sensible defaults.

⚠️ Always Check the error Property:
When using the softFail or defaultResponse strategies, the promise will not throw on error. You must always check the error property in the response object to detect and handle errors.

import { fetchf } from 'fetchff';

const { data, error } = await fetchf(
  'https://api.example.com/user-preferences',
  {
    strategy: 'defaultResponse',
    defaultResponse: {
      theme: 'light',
      language: 'en',
      notifications: true,
    },
    timeout: 5000,
  },
);

if (error) {
  console.warn('Failed to load user preferences, using defaults:', data);
  // Log error for debugging but continue with default values
  console.error('Preferences API error:', error.message);
} else {
  console.log('User preferences loaded:', data);
}

// Safe to use data regardless of error state
document.body.className = data.theme;

silent:
Hangs the promise silently on error, useful for fire-and-forget requests without the need for try/catch. In case of an error, the promise will never be resolved or rejected, and any code after will never be executed. This strategy is useful for dispatching requests within asynchronous wrapper functions that do not need to be awaited. It prevents excessive usage of try/catch or additional response data checks everywhere. It can be used in combination with onError to handle errors separately.

⚠️ When using in Node.js:
The 'silent' strategy will hang the promise forever. Use with caution, especially in backend/server environments.

async function myLoadingProcess() {
  const { data } = await fetchf('https://api.example.com/', {
    strategy: 'silent',
  });

  // In case of an error nothing below will ever be executed.
  console.log('This console log will not appear.');
}

myLoadingProcess();

How It Works

1. Reject Strategy:
   When using the reject strategy, if an error occurs, the promise is rejected, and global error handling logic is triggered. You must use try/catch to handle these errors.

2. Soft Fail Strategy:
   With softFail, the response object includes additional properties that provide details about the error without rejecting the promise. This allows you to handle error information directly within the response.

3. Default Response Strategy:
   The defaultResponse strategy returns a predefined default response when an error occurs. This approach prevents the promise from being rejected, allowing for default values to be used in place of error data.

4. Silent Strategy:
   The silent strategy results in the promise hanging silently on error. The promise will not be resolved or rejected, and any subsequent code will not execute. This is useful for fire-and-forget requests and can be combined with onError for separate error handling.

5. Custom Error Handling:
   Depending on the strategy chosen, you can tailor how errors are managed, either by handling them directly within response objects, using default responses, or managing them silently.

🎯 Choosing the Right Error Strategy

Understanding when to use each error handling strategy is crucial for building robust applications:

reject Strategy - Traditional Error Handling

When to Use:

• Building applications with established error boundaries
• Need consistent error propagation through promise chains
• Integration with existing try/catch error handling patterns
• Critical operations where failures must be explicitly handled

Best For:

// API calls where failure must stop execution
try {
  const { data } = await fetchf('/api/payment/process', {
    method: 'POST',
    body: paymentData,
    strategy: 'reject', // Default - can be omitted
  });

  // Only proceed if payment succeeded
  await processOrderCompletion(data);
} catch (error) {
  // Handle payment failure explicitly
  showPaymentErrorModal(error.message);
  revertOrderState();
}

softFail Strategy - Graceful Error Handling

When to Use:

• Building user-friendly interfaces that degrade gracefully
• Multiple API calls where some failures are acceptable
• React/Vue components that need to handle loading/error states
• Data fetching where partial failures shouldn't break the UI

Best For:

// Dashboard with multiple data sources
const { data: userStats, error: statsError } = await fetchf('/api/user/stats', {
  strategy: 'softFail',
});
const { data: notifications, error: notifError } = await fetchf('/api/notifications', {
  strategy: 'softFail',
});

// Render what we can, gracefully handle what failed
return (
  <Dashboard>
    {userStats && <StatsWidget data={userStats} />}
    {statsError && <ErrorMessage>Stats temporarily unavailable</ErrorMessage>}

    {notifications && <NotificationsList data={notifications} />}
    {notifError && <ErrorMessage>Notifications unavailable</ErrorMessage>}
  </Dashboard>
);

defaultResponse Strategy - Fallback Values

When to Use:

• Optional features that should work even when API fails
• Configuration or preferences that have sensible defaults
• Non-critical data that can fall back to static values
• Progressive enhancement scenarios

Best For:

// User preferences with fallbacks
const { data: preferences } = await fetchf('/api/user/preferences', {
  strategy: 'defaultResponse',
  defaultResponse: {
    theme: 'light',
    language: 'en',
    notifications: true,
    autoSave: false,
  },
});

// Safe to use preferences regardless of API status
applyTheme(preferences.theme);
setLanguage(preferences.language);

silent Strategy - Fire-and-Forget

When to Use:

• Analytics and telemetry data
• Non-critical background operations
• Optional data prefetching
• Logging and monitoring calls

Best For:

// Analytics tracking (don't let failures affect user experience)
const trackUserAction = (action: string, data: any) => {
  fetchf('/api/analytics/track', {
    method: 'POST',
    body: { action, data, timestamp: Date.now() },
    strategy: 'silent',
    onError(error) {
      // Log error for debugging, but don't disrupt user flow
      console.warn('Analytics tracking failed:', error.message);
    },
  });

  // This function never throws, never shows loading states
  // User interaction continues uninterrupted
};

// Background data prefetching
const prefetchNextPage = () => {
  fetchf('/api/articles/page/2', {
    strategy: 'silent',
    cacheTime: 300, // Cache for later use
  });
  // No need to await or handle response
};

📊 Performance Strategy Matrix

Choose strategies based on your application's needs:

Use Case	Strategy	Benefits	Trade-offs
Critical Operations	reject	Explicit error handling, prevents data corruption	Requires try/catch, can break user flow
UI Components	softFail	Graceful degradation, better UX	Need to check error property
Optional Features	defaultResponse	Always provides usable data	May mask real issues
Background Tasks	silent	Never disrupts user experience	Errors may go unnoticed

🔧 Advanced Strategy Patterns

Hybrid Error Handling

// Combine strategies for optimal UX
const fetchUserDashboard = async (userId: string) => {
  // Critical user data - must succeed
  const { data: userData } = await fetchf(`/api/users/${userId}`, {
    strategy: 'reject',
  });

  // Optional widgets - graceful degradation
  const { data: stats, error: statsError } = await fetchf(
    `/api/users/${userId}/stats`,
    {
      strategy: 'softFail',
    },
  );

  // Preferences with fallbacks
  const { data: preferences } = await fetchf(
    `/api/users/${userId}/preferences`,
    {
      strategy: 'defaultResponse',
      defaultResponse: DEFAULT_USER_PREFERENCES,
    },
  );

  // Background analytics - fire and forget
  fetchf('/api/analytics/dashboard-view', {
    method: 'POST',
    body: { userId, timestamp: Date.now() },
    strategy: 'silent',
  });

  return { userData, stats, statsError, preferences };
};

Progressive Enhancement

// Start with defaults, enhance with API data
const enhanceWithApiData = async () => {
  // Immediate render with defaults
  let config = DEFAULT_APP_CONFIG;
  renderApp(config);

  // Enhance with API data when available
  const { data: apiConfig } = await fetchf('/api/config', {
    strategy: 'defaultResponse',
    defaultResponse: DEFAULT_APP_CONFIG,
  });

  // Re-render with enhanced config
  config = { ...config, ...apiConfig };
  renderApp(config);
};

onError

The onError option can be configured to intercept errors:

const { data } = await fetchf('https://api.example.com/', {
  strategy: 'softFail',
  onError(error) {
    // Intercept any error
    console.error('Request failed', error.status, error.statusText);
  },
});

Different Error and Success Responses

There might be scenarios when your successful response data structure differs from the one that is on error. In such circumstances you can use union type and assign it depending on if it's an error or not.

interface SuccessResponseData {
  bookId: string;
  bookText: string;
}

interface ErrorResponseData {
  errorCode: number;
  errorText: string;
}

type ResponseData = SuccessResponseData | ErrorResponseData;

const { data, error } = await fetchf<ResponseData>('https://api.example.com/', {
  strategy: 'softFail',
});

// Check for error here as 'data' is available for both successful and erroneous responses
if (error) {
  const errorData = data as ErrorResponseData;

  console.log('Request failed', errorData.errorCode, errorData.errorText);
} else {
  const successData = data as SuccessResponseData;

  console.log('Request successful', successData.bookText);
}

📦 Typings

Click to expand

The fetchff package provides comprehensive TypeScript typings to enhance development experience and ensure type safety. Below are details on the available, exportable types for both createApiFetcher() and fetchf().

Typings for fetchf<RequestType>()

The fetchf() function includes types that help configure and manage network requests effectively:

interface AddBookRequest {
  response: AddBookResponseData;
  params: AddBookQueryParams;
  urlPathParams: AddBookPathParams;
  body: AddBookRequestBody;
}

// You could also use: fetchf<Req<AddBookResponseData>> as a shorthand so not to create additional request interface
const { data: book } = await fetchf<AddBookRequest>('/api/add-book', {
  method: 'POST',
});
// Your book is of type AddBookResponseData

• Req<ResponseData, RequestBody, QueryParams, UrlPathParams>: Represents a shorter 4-generics version of request object type for endpoints, allowing you to compose the shape of the request payload, query parameters, and path parameters for each request using a couple inline generics e.g. fetchf<ResponseData, RequestBody, QueryParams, UrlPathParams>(). While there is no plan for deprecation, this is for compatibility with older versions only. Aim to use the new method with single generic presented above instead. We don't use overload here to keep it all fast and snappy.
• RequestConfig: Main configuration options for the fetchf() function, including request settings, interceptors, and retry configurations.
• RetryConfig: Configuration options for retry mechanisms, including the number of retries, delay between retries, and backoff strategies.
• CacheConfig: Configuration options for caching, including cache time, custom cache keys, and cache invalidation rules.
• PollingConfig: Configuration options for polling, including polling intervals and conditions to stop polling.
• ErrorStrategy: Defines strategies for handling errors, such as rejection, soft fail, default response, and silent modes.

For a complete list of types and their definitions, refer to the request-handler.ts file.

Typings for createApiFetcher()

The createApiFetcher<EndpointTypes>() function provides a robust set of types to define and manage API interactions.

• EndpointTypes: Represents the list of API endpoints with their respective settings. It is your own interface that you can pass to this generic. It will be cross-checked against the endpoints object in your createApiFetcher() configuration. Each endpoint can be configured with its own specific types such as Response Data Structure, Query Parameters, URL Path Parameters or Request Body. Example:

interface EndpointTypes {
  fetchBook: Endpoint<{
    response: Book;
    params: BookQueryParams;
    urlPathParams: BookPathParams;
  }>;
  // or shorter version: fetchBook: EndpointReq<Book, undefined, BookQueryParams, BookPathParams>;
  addBook: Endpoint<{
    response: Book;
    body: BookBody;
    params: BookQueryParams;
    urlPathParams: BookPathParams;
  }>;
  // or shorter version: fetchBook: EndpointReq<Book, BookBody, BookQueryParams, BookPathParams>;
  someOtherEndpoint: Endpoint; // The generic is fully optional but it must be defined for endpoint not to output error
}

const api = createApiFetcher<EndpointTypes>({
  baseURL: 'https://example.com/api',
  endpoints: {
    fetchBook: {
      url: '/get-book',
    },
    addBook: {
      url: '/add-book',
      method: 'POST',
    },
  },
});

const { data: book } = await api.addBook();
// book will be of type Book

• Endpoint<{response: ResponseData, params: QueryParams, urlPathParams: PathParams, body: RequestBody}>: Represents an API endpoint function, allowing to be defined with optional response data (default DefaultResponse), query parameters (default QueryParams), URL path parameters (default DefaultUrlParams), and request body (default DefaultPayload).
• RequestInterceptor: Function to modify request configurations before they are sent.
• ResponseInterceptor: Function to process responses before they are handled by the application.
• ErrorInterceptor: Function to handle errors when a request fails.
• CustomFetcher: Represents the custom fetcher function.

For a full list of types and detailed definitions, refer to the api-handler.ts file.

Generic Typings

The fetchff package includes several generic types to handle various aspects of API requests and responses:

• QueryParams<ParamsType>: Represents query parameters for requests. Can be an object, URLSearchParams, an array of name-value pairs, or null.
• BodyPayload<PayloadType>: Represents the request body. Can be BodyInit, an object, an array, a string, or null.
• UrlPathParams<UrlParamsType>: Represents URL path parameters. Can be an object or null.
• DefaultResponse: Default response for all requests. Default is: any.

Benefits of Using Typings

• Type Safety: Ensures that configurations and requests adhere to expected formats, reducing runtime errors and improving reliability.
• Autocompletion: Provides better support for autocompletion in editors, making development faster and more intuitive.
• Documentation: Helps in understanding available options and their expected values, improving code clarity and maintainability.

🔒 Sanitization

Click to expand

FetchFF includes robust built-in sanitization mechanisms that protect your application from common security vulnerabilities. These safeguards are automatically applied without requiring any additional configuration.

Prototype Pollution Prevention

The library implements automatic protection against prototype pollution attacks by:

• Removing dangerous properties like __proto__, constructor, and prototype from objects
• Sanitizing all user-provided data before processing it

// Example of protection against prototype pollution
const userInput = {
  id: 123,
  __proto__: { malicious: true },
};

// The sanitization happens automatically
const response = await fetchf('/api/users', {
  params: userInput, // The __proto__ property will be removed
});

Input Sanitization Features

1. Object Sanitization

   • All incoming objects are sanitized via the sanitizeObject utility
   • Creates shallow copies of input objects with dangerous properties removed
   • Applied automatically to request configurations, headers, and other objects

2. URL Parameter Safety

   • Path parameters are properly encoded using encodeURIComponent
   • Query parameters are safely serialized and encoded
   • Prevents URL injection attacks and ensures valid URL formatting

3. Data Validation

   • Checks for JSON serializability of request bodies
   • Detects circular references that could cause issues
   • Properly handles different data types (strings, arrays, objects, etc.)

4. Depth Control

   • Prevents excessive recursion with depth limitations
   • Mitigates stack overflow attacks through query parameter manipulation
   • Maximum depth is controlled by MAX_DEPTH constant (default: 10)

Implementation Details

The sanitization process is applied at multiple levels:

• During request configuration building
• When processing URL path parameters
• When serializing query parameters
• When handling request and response interceptors
• During retry and polling operations

This multi-layered approach ensures that all data passing through the library is properly sanitized, significantly reducing the risk of injection attacks and other security vulnerabilities.

// Example of safe URL path parameter handling
const { data } = await api.getUser({
  urlPathParams: {
    id: 'user-id with spaces & special chars',
  },
  // Automatically encoded to: /users/user-id%20with%20spaces%20%26%20special%20chars
});

Security is a core design principle of FetchFF, with sanitization mechanisms running automatically to provide protection without adding complexity to your code.

⚛️ React Integration

Click to expand

FetchFF offers a high-performance React hook, useFetcher(url, config), for efficient data fetching in React applications. This hook provides built-in caching, automatic request deduplication, comprehensive state management etc. Its API mirrors the native fetch and fetchf(url, config) signatures, allowing you to pass all standard and advanced configuration options seamlessly. Designed with React best practices in mind, useFetcher ensures optimal performance and a smooth developer experience.

Basic Usage

import { useFetcher } from 'fetchff/react';

function UserProfile({ userId }: { userId: string }) {
  const { data, error, isLoading, refetch } = useFetcher(
    `/api/users/${userId}`,
  );

  if (isLoading) return <div>Loading...</div>;
  if (error) return <div>Error: {error.message}</div>;

  return (
    <div>
      <h1>{data.name}</h1>
      <button onClick={refetch}>Refresh</button>
    </div>
  );
}

Hook API

The useFetcher(url, config) hook returns an object with the following properties:

• data: ResponseData | null
  The fetched data, typed as T (generic), or null if not available.
• error: ResponseError | null
  Error object if the request failed, otherwise null.
• isLoading: boolean
true while data is being loaded for the first time or during a fetch.
• isFetching: boolean
true when currently fetching (fetch is in progress).
• config: RequestConfig
  The configuration object used for the request.
• headers: Record<string, string>
  Response headers from the last successful request.
• refetch: (forceRefresh: boolean = true) => Promise<FetchResponse<ResponseData, RequestBody, QueryParams, PathParams> | null>
  Function to manually trigger a new request. It always uses softFail strategy and returns a new FetchResponse object. The forceRefresh is set to true by default - it will bypass cache and force new request and cache refresh.
• mutate: (data: ResponseData, settings: MutationSettings) => Promise<FetchResponse<ResponseData, RequestBody, QueryParams, PathParams> | null>
  Function to update cached data directly, by passing new data. The settings object contains currently revalidate (boolean) property. If set to true, a new request will be made after cache and component data are updated.

Configuration Options

All standard FetchFF options are supported, plus React-specific features:

const { data, error, isLoading } = useFetcher('/api/data', {
  // Cache for 5 minutes
  cacheTime: 300,

  // Deduplicate requests within 2 seconds
  dedupeTime: 2000,

  // Revalidate when window regains focus
  refetchOnFocus: true,

  // Don't fetch immediately (useful for POST requests; React specific)
  immediate: false,

  // Custom error handling
  strategy: 'softFail',

  // Request configuration
  method: 'POST',
  body: { name: 'John' },
  headers: { Authorization: 'Bearer token' },
});

Note on immediate behavior: By default, only GET and HEAD requests (RFC 7231 safe methods) trigger automatically when the component mounts. Other HTTP methods like POST, PUT, DELETE require either setting immediate: true explicitly or calling refetch() manually. This prevents unintended side effects from automatic execution of non-safe HTTP operations.

Conditional Requests

Only fetch when conditions are met (immediate option is true):

function ConditionalData({
  shouldFetch,
  userId,
}: {
  shouldFetch: boolean;
  userId?: string;
}) {
  const { data, isLoading } = useFetcher(`/api/users/${userId}`, {
    immediate: shouldFetch && !!userId,
  });

  // Will only fetch when shouldFetch is true and userId exists
  return <div>{data ? data.name : 'No data'}</div>;
}

You can also pass null as the URL to conditionally skip a request:

function ConditionalData({
  shouldFetch,
  userId,
}: {
  shouldFetch: boolean;
  userId?: string;
}) {
  const { data, isLoading } = useFetcher(
    shouldFetch && userId ? `/api/users/${userId}` : null,
  );

  // Will only fetch when shouldFetch is true and userId exists
  return <div>{data ? data.name : 'No data'}</div>;
}

Note: Passing null as the URL to conditionally skip a request is a legacy/deprecated approach (commonly used in SWR plugin). For new code, prefer using the immediate option for conditional fetching. The null URL method is still supported for backwards compatibility.

Dynamic URLs and Parameters

function SearchResults({ query }: { query: string }) {
  const { data, isLoading } = useFetcher('/api/search', {
    params: { q: query, limit: 10 },
    // Only fetch when query exists
    immediate: !!query,
  });

  return (
    <div>
      {isLoading && <div>Searching...</div>}
      {data?.results?.map((item) => (
        <div key={item.id}>{item.title}</div>
      ))}
    </div>
  );
}

Mutations and Cache Updates

function TodoList() {
  const { data: todos, mutate, refetch } = useFetcher('/api/todos');

  const addTodo = async (text: string) => {
    // Optimistically update the cache
    const newTodo = { id: Date.now(), text, completed: false };
    mutate([...todos, newTodo]);

    try {
      // Make the actual request
      await fetchf('/api/todos', {
        method: 'POST',
        body: { text },
      });

      // Revalidate to get the real data
      refetch();
    } catch (error) {
      // Revert on error
      mutate(todos);
    }
  };

  return (
    <div>
      {todos?.map((todo) => (
        <div key={todo.id}>{todo.text}</div>
      ))}
      <button onClick={() => addTodo('New todo')}>Add Todo</button>
    </div>
  );
}

Error Handling

function DataWithErrorHandling() {
  const { data, error, isLoading, refetch } = useFetcher('/api/data', {
    retry: {
      retries: 3,
      delay: 1000,
      backoff: 1.5,
    },
  });

  if (isLoading) return <div>Loading...</div>;

  if (error) {
    return (
      <div>
        <p>Error: {error.message}</p>
        <button onClick={refetch}>Try Again</button>
      </div>
    );
  }

  return <div>{JSON.stringify(data)}</div>;
}

Suspense Support

Use with React Suspense for declarative loading states:

import { Suspense } from 'react';

function DataComponent() {
  const { data } = useFetcher('/api/data', {
    strategy: 'reject', // Required for Suspense
  });

  return <div>{data.title}</div>;
}

function App() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <DataComponent />
    </Suspense>
  );
}

TypeScript Support

Full TypeScript support with automatic type inference:

interface User {
  id: number;
  name: string;
  email: string;
}

interface UserParams {
  include?: string[];
}

function UserComponent({ userId }: { userId: string }) {
  const { data, error } = useFetcher<User>(`/api/users/${userId}`, {
    params: { include: ['profile', 'settings'] } as UserParams,
  });

  // data is automatically typed as User | null
  // error is typed as ResponseError | null

  return <div>{data?.name}</div>;
}

Performance Features

• Automatic deduplication: Multiple components requesting the same data share a single request
• Smart caching: Configurable cache with automatic invalidation
• Minimal re-renders: Optimized to prevent unnecessary component updates (relies on native React functionality)
• Background revalidation: Keep data fresh without blocking the UI (use staleTime setting to control the time)

Best Practices

1. Use conditional requests for dependent data:

const { data: user } = useFetcher('/api/user');
const { data: posts } = useFetcher(user ? `/api/users/${user.id}/posts` : null);

2. Configure appropriate cache times based on data volatility:

// Static data - cache for 1 hour
const { data: config } = useFetcher('/api/config', { cacheTime: 3600 });

// Dynamic data - cache for 30 seconds
const { data: feed } = useFetcher('/api/feed', { cacheTime: 30 });

3. Use focus revalidation for critical data:

const { data } = useFetcher('/api/critical-data', {
  refetchOnFocus: true,
});

4. Handle loading and error states appropriately:

const { data, error, isLoading } = useFetcher('/api/data');

if (isLoading) return <Spinner />;
if (error) return <ErrorMessage error={error} />;
return <DataDisplay data={data} />;

5. Leverage staleTime to control background revalidation:

// Data is considered fresh for 10 minutes; background revalidation happens after
const { data } = useFetcher('/api/notifications', { staleTime: 600 });

• Use a longer staleTime for rarely changing data to minimize unnecessary network requests.
• Use a shorter staleTime for frequently updated data to keep the UI fresh.
• Setting staleTime: 0 disables the staleTime (default).
• Combine staleTime with cacheTime for fine-grained cache and revalidation control.
• Adjust staleTime per endpoint based on how critical or dynamic the data is.

Comparison with other libraries

fetchff uniquely combines advanced input sanitization, prototype pollution protection, unified cache across React and direct fetches, multiple error handling strategies, and a declarative API repository pattern—all in a single lightweight package.

Feature	fetchff	ofetch	wretch	axios	native fetch()	swr
Unified API Client	✅	--	--	--	--	--
Smart Request Cache	✅	--	--	--	--	✅
Automatic Request Deduplication	✅	--	--	--	--	✅
Revalidation on Window Focus	✅	--	--	--	--	✅
Custom Fetching Adapter	✅	--	--	--	--	✅
Built-in Error Handling	✅	--	✅	--	--	--
Customizable Error Handling	✅	--	✅	✅	--	✅
Retries with exponential backoff	✅	--	--	--	--	--
Advanced Query Params handling	✅	--	--	--	--	--
Custom Response Based Retry logic	✅	✅	✅	--	--	--
Easy Timeouts	✅	✅	✅	✅	--	--
Adaptive Timeouts (Connection-aware)	✅	--	--	--	--	--
Conditional Polling Functionality	✅	--	--	--	--	--
Easy Cancellation of stale (previous) requests	✅	--	--	--	--	--
Default Responses	✅	--	--	--	--	✅
Custom adapters (fetchers)	✅	--	--	✅	--	✅
Global Configuration	✅	--	✅	✅	--	✅
TypeScript Support	✅	✅	✅	✅	✅	✅
Built-in AbortController Support	✅	--	--	--	--	--
Request Interceptors	✅	✅	✅	✅	--	--
Safe deduping + cancellation	✅	--	--	--	--	--
Response-based polling decisions	✅	--	--	--	--	--
Request/Response Data Transformation	✅	✅	✅	✅	--	--
Works with Multiple Frameworks	✅	✅	✅	✅	✅	--
Works across multiple instances or layers	✅	--	--	--	--	-- (only React)
Concurrent Request Deduplication	✅	--	--	--	--	✅
Flexible Error Handling Strategies	✅	--	✅	✅	--	✅
Dynamic URLs with Path and query separation	✅	--	✅	--	--	--
Automatic Retry on Failure	✅	✅	--	✅	--	✅
Automatically handle 429 Retry-After headers	✅	--	--	--	--	--
Built-in Input Sanitization	✅	--	--	--	--	--
Prototype Pollution Protection	✅	--	--	--	--	--
RFC 7231 Safe Methods Auto-execution	✅	--	--	--	--	--
First Class React Integration	✅	--	--	--	--	✅
Shared cache for React and direct fetches	✅	--	--	--	--	--
Per-endpoint and per-request config merging	✅	--	--	--	--	--
Declarative API repository pattern	✅	--	--	--	--	--
Supports Server-Side Rendering (SSR)	✅	✅	✅	✅	✅	✅
SWR Pattern Support	✅	--	--	--	--	✅
Revalidation on Tab Focus	✅	--	--	--	--	✅
Revalidation on Network Reconnect	✅	--	--	--	--	✅
Minimal Installation Size	🟢 (5.2 KB)	🟡 (6.5 KB)	🟢 (2.21 KB)	🔴 (13.7 KB)	🟢 (0 KB)	🟡 (6.2 KB)

✏️ Examples

Click to expand particular examples below. You can also check docs/examples/ for more examples of usage.

All Settings

Click to expand

Here’s an example of configuring and using the createApiFetcher() with all available settings.

const api = createApiFetcher({
  baseURL: 'https://api.example.com/',
  endpoints: {
    getBooks: {
      url: 'books/all',
      method: 'get',
      cancellable: true,
      // All the global settings can be specified on per-endpoint basis as well
    },
  },
  strategy: 'reject', // Error handling strategy.
  cancellable: false, // If true, cancels previous requests to same endpoint.
  rejectCancelled: false, // Reject promise for cancelled requests.
  flattenResponse: false, // If true, flatten nested response data.
  defaultResponse: null, // Default response when there is no data or endpoint fails.
  withCredentials: true, // Pass cookies to all requests.
  timeout: 30000, // Request timeout in milliseconds. Defaults to 30s (60s on slow connections), can be overridden.
  dedupeTime: 0, // Time window, in milliseconds, during which identical requests are deduplicated (treated as single request).
  immediate: false, // If false, disables automatic request on initialization (useful for POST or conditional requests, React-specific)
  staleTime: 600, // Data is considered fresh for 10 minutes before background revalidation (disabled by default)
  pollingInterval: 5000, // Interval in milliseconds between polling attempts. Setting 0 disables polling.
  pollingDelay: 1000, // Wait 1 second before beginning each polling attempt
  maxPollingAttempts: 10, // Stop polling after 10 attempts
  shouldStopPolling: (response, attempt) => false, // Function to determine if polling should stop based on the response. Return true to stop polling, or false to continue.
  method: 'get', // Default request method.
  params: {}, // Default params added to all requests.
  urlPathParams: {}, // Dynamic URL path parameters for replacing segments like /user/:id
  data: {}, // Alias for 'body'. Default data passed to POST, PUT, DELETE and PATCH requests.
  cacheTime: 300, // Cache time in seconds. In this case it is valid for 5 minutes (300 seconds)
  cacheKey: (config) => `${config.url}-${config.method}`, // Custom cache key based on URL and method
  cacheBuster: (config) => config.method === 'POST', // Bust cache for POST requests
  skipCache: (response, config) => response.status !== 200, // Skip caching on non-200 responses
  cacheErrors: false, // Cache error responses as well as successful ones, default false
  onError(error) {
    // Interceptor on error
    console.error('Request failed', error);
  },
  async onRequest(config) {
    // Interceptor on each request
    console.error('Fired on each request', config);
  },
  async onResponse(response) {
    // Interceptor on each response
    console.error('Fired on each response', response);
  },
  logger: {
    // Custom logger for logging errors.
    error(...args) {
      console.log('My custom error log', ...args);
    },
    warn(...args) {
      console.log('My custom warning log', ...args);
    },
  },
  retry: {
    retries: 3, // Number of retries on failure.
    delay: 1000, // Initial delay between retries in milliseconds. Defaults to 1s (2s on slow connections), can be overridden.
    backoff: 1.5, // Backoff factor for retry delay.
    maxDelay: 30000, // Maximum delay between retries in milliseconds. Defaults to 30s (60s on slow connections), can be overridden.
    resetTimeout: true, // Reset the timeout when retrying requests.
    retryOn: [408, 409, 425, 429, 500, 502, 503, 504], // HTTP status codes to retry on.
    shouldRetry: async (response, attempts) => {
      // Custom retry logic.
      return (
        attempts < 3 &&
        [408, 500, 502, 503, 504].includes(response.error.status)
      );
    },
  },
});

try {
  // The same API config as used above, except the "endpoints" and "fetcher" and fetcher could be used as 3rd argument of the api.getBooks()
  const { data } = await api.getBooks();
  console.log('Request succeeded:', data);
} catch (error) {
  console.error('Request ultimately failed:', error);
}

Examples Using createApiFetcher()

All examples below are with usage of createApiFetcher(). You can also use fetchf() independently.

Multiple APIs Handler from different API sources

Click to expand

import { createApiFetcher } from 'fetchff';

// Create fetcher instance
const api = createApiFetcher({
  baseURL: 'https://example.com/api/v1',
  endpoints: {
    sendMessage: {
      method: 'post',
      url: '/send-message/:postId',
    },
    getMessage: {
      url: '/get-message/',
      // Change baseURL to external for this endpoint only
      baseURL: 'https://externalprovider.com/api/v2',
    },
  },
});

// Make a wrapper function and call your API
async function sendAndGetMessage() {
  await api.sendMessage({
    body: { message: 'Text' },
    urlPathParams: { postId: 1 },
  });

  const { data } = await api.getMessage({
    params: { postId: 1 },
  });
}

// Invoke your wrapper function
sendAndGetMessage();

Using with Full TypeScript Support

Click to expand

The library includes all necessary TypeScript definitions bringing full TypeScript support to your API Handler. The package ships interfaces with sensible defaults making it easier to add new endpoints.

// books.d.ts
interface Book {
  id: number;
  title: string;
  rating: number;
}

interface Books {
  books: Book[];
  totalResults: number;
}

interface BookQueryParams {
  newBook?: boolean;
  category?: string;
}

interface BookPathParams {
  bookId: number;
}

// api.ts
import type { Endpoint } from 'fetchff';
import { createApiFetcher } from 'fetchff';

const endpoints = {
  fetchBooks: {
    url: '/books',
    method: 'GET' as const,
  },
  fetchBook: {
    url: '/books/:bookId',
    method: 'GET' as const,
  },
} as const;

// Define endpoints with proper typing
interface EndpointTypes {
  fetchBook: Endpoint<{
    response: Book;
    params: BookQueryParams;
    urlPathParams: BookPathParams;
  }>;
  fetchBooks: Endpoint<{ response: Books; params: BookQueryParams }>;
}

const api = createApiFetcher<EndpointTypes>({
  baseURL: 'https://example.com/api',
  strategy: 'softFail',
  endpoints,
});

export { api };
export type { Book, Books, BookQueryParams, BookPathParams };

// Usage with full type safety
import { api, type Book, type Books } from './api';

// Properly typed request with URL params
const book = await api.fetchBook({
  params: { newBook: true },
  urlPathParams: { bookId: 1 },
});

if (book.error) {
  console.error('Failed to fetch book:', book.error.message);
} else {
  console.log('Book title:', book.data?.title);
}

// For example, this will cause a TypeScript error as 'rating' doesn't exist in BookQueryParams
// const invalidBook = await api.fetchBook({
//   params: { rating: 5 }
// });

// Generic type can be passed directly for additional type safety
const books = await api.fetchBooks<Books>({
  params: { category: 'fiction' },
});

if (books.error) {
  console.error('Failed to fetch books:', books.error.message);
} else {
  console.log('Total books:', books.data?.totalResults);
}

Using with TypeScript and Custom Headers

Click to expand

import { createApiFetcher } from 'fetchff';

const endpoints = {
  getPosts: {
    url: '/posts/:subject',
  },
  getUser: {
    // Generally there is no need to specify method: 'get' for GET requests as it is default one. It can be adjusted using global "method" setting
    method: 'get',
    url: '/user-details',
  },
  updateUserDetails: {
    method: 'post',
    url: '/user-details/update/:userId',
    strategy: 'defaultResponse',
  },
};

interface PostsResponse {
  posts: Array<{ id: number; title: string; content: string }>;
  totalCount: number;
}

interface PostsQueryParams {
  additionalInfo?: string;
  limit?: number;
}

interface PostsPathParams {
  subject: string;
}

interface EndpointTypes {
  getPosts: Endpoint<{
    response: PostsResponse;
    params: PostsQueryParams;
    urlPathParams: PostsPathParams;
  }>;
}

const api = createApiFetcher<EndpointTypes>({
  baseURL: 'https://example.com/api',
  endpoints,
  onError(error) {
    console.log('Request failed', error);
  },
  headers: {
    'my-auth-key': 'example-auth-key-32rjjfa',
  },
});

// Fetch user data - "data" will return data directly
// GET to: https://example.com/api/user-details?userId=1&ratings[]=1&ratings[]=2
const { data } = await api.getUser({
  params: { userId: 1, ratings: [1, 2] },
});

// Fetch posts - "data" will return data directly
// GET to: https://example.com/api/posts/test?additionalInfo=something
const { data: postsData } = await api.getPosts({
  params: { additionalInfo: 'something' },
  urlPathParams: { subject: 'test' },
});

// Send POST request to update userId "1"
await api.updateUserDetails({
  body: { name: 'Mark' },
  urlPathParams: { userId: 1 },
});

// Send POST request to update array of user ratings for userId "1"
await api.updateUserDetails({
  body: { name: 'Mark', ratings: [1, 2] },
  urlPathParams: { userId: 1 },
});

In the example above we fetch data from an API for user with an ID of 1. We also make a GET request to fetch some posts, update user's name to Mark. If you want to use more strict typings, please check TypeScript Usage section below.

Custom Fetcher

Click to expand

import { createApiFetcher } from 'fetchff';

// Create the API fetcher with the custom fetcher
const api = createApiFetcher({
  baseURL: 'https://api.example.com/',
  retry: retryConfig,
  // This function will be called whenever a request is being fired.
  async fetcher(config) {
    // Implement your custom fetch logic here
    const response = await fetch(config.url, config);
    // Optionally, process or transform the response
    return response;
  },
  endpoints: {
    getBooks: {
      url: 'books/all',
      method: 'get',
      cancellable: true,
      // All the global settings can be specified on per-endpoint basis as well
    },
  },
});

Error handling strategy - reject (default)

Click to expand

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    sendMessage: {
      method: 'post',
      url: '/send-message/:postId',
      strategy: 'reject', // It is a default strategy so it does not really need to be here
    },
  },
});

async function sendMessage() {
  try {
    await api.sendMessage({
      body: { message: 'Text' },
      urlPathParams: { postId: 1 },
    });

    console.log('Message sent successfully');
  } catch (error) {
    console.error('Message failed to send:', error.message);
  }
}

sendMessage();

Error handling strategy - softFail

Click to expand

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    sendMessage: {
      method: 'post',
      url: '/send-message/:postId',
      strategy: 'softFail', // Returns a response object with additional error details without rejecting the promise.
    },
  },
});

async function sendMessage() {
  const { data, error } = await api.sendMessage({
    body: { message: 'Text' },
    urlPathParams: { postId: 1 },
  });

  if (error) {
    console.error('Request Error', error.message);
  } else {
    console.log('Message sent successfully:', data);
  }
}

sendMessage();

Error handling strategy - defaultResponse

Click to expand

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    sendMessage: {
      method: 'post',
      url: '/send-message/:postId',
      // You can also specify strategy and other settings in global list of endpoints, but just for this endpoint
      // strategy: 'defaultResponse',
    },
  },
});

async function sendMessage() {
  const { data, error } = await api.sendMessage({
    body: { message: 'Text' },
    urlPathParams: { postId: 1 },
    strategy: 'defaultResponse',
    // null is a default setting, you can change it to empty {} or anything
    defaultResponse: { status: 'failed', message: 'Default response' },
    onError(error) {
      // Callback is still triggered here
      console.error('API error:', error.message);
    },
  });

  if (error) {
    console.warn('Message failed to send, using default response:', data);
    return;
  }

  console.log('Message sent successfully:', data);
}

sendMessage();

Error handling strategy - silent

Click to expand

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    sendMessage: {
      method: 'post',
      url: '/send-message/:postId',
      // You can also specify strategy and other settings in here, just for this endpoint
      // strategy: 'silent',
    },
  },
});

async function sendMessage() {
  await api.sendMessage({
    body: { message: 'Text' },
    urlPathParams: { postId: 1 },
    strategy: 'silent',
    onError(error) {
      console.error('Silent error logged:', error.message);
    },
  });

  // Because of the strategy, if API call fails, it will never reach this point. Otherwise try/catch would need to be required.
  console.log('Message sent successfully');
}

// Note that since strategy is "silent" and sendMessage should not be awaited anywhere
sendMessage();

onError Interceptor

Click to expand

import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    sendMessage: {
      method: 'post',
      url: '/send-message/:postId',
    },
  },
});

async function sendMessage() {
  try {
    await api.sendMessage({
      body: { message: 'Text' },
      urlPathParams: { postId: 1 },
      onError(error) {
        console.error('Error intercepted:', error.message);
        console.error('Response:', error.response);
        console.error('Config:', error.config);
      },
    });

    console.log('Message sent successfully');
  } catch (error) {
    console.error('Final error handler:', error.message);
  }
}

sendMessage();

Request Chaining

Click to expand

In this example, we make an initial request to get a user's details, then use that data to fetch additional information in a subsequent request. This pattern allows you to perform multiple asynchronous operations in sequence, using the result of one request to drive the next.

import { createApiFetcher } from 'fetchff';

// Initialize API fetcher with endpoints
const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    getUser: { url: '/user' },
    createPost: { url: '/post', method: 'POST' },
  },
});

async function fetchUserAndCreatePost(userId: number, postData: any) {
  // Fetch user data
  const { data: userData } = await api.getUser({ params: { userId } });

  // Create a new post with the fetched user data
  return await api.createPost({
    body: {
      ...postData,
      userId: userData.id, // Use the user's ID from the response
    },
  });
}

// Example usage
fetchUserAndCreatePost(1, { title: 'New Post', content: 'This is a new post.' })
  .then((response) => console.log('Post created:', response))
  .catch((error) => console.error('Error:', error));

Example Usage in Node.js

Using with Express.js / Fastify

Click to expand

import { fetchf } from 'fetchff';

app.get('/api/proxy', async (req, res) => {
  const { data, error } = await fetchf('https://external.api/resource');
  if (error) {
    return res.status(error.status).json({ error: error.message });
  }
  res.json(data);
});

Example Usage with Frameworks and Libraries

fetchff is designed to seamlessly integrate with any popular frameworks like Next.js, libraries like React, Vue, React Query and SWR. It is written in pure JS so you can effortlessly manage API requests with minimal setup, and without any dependencies.

Advanced Caching Strategies

Click to expand

import { fetchf, mutate, deleteCache } from 'fetchff';

// Example: User dashboard with smart caching
const fetchUserDashboard = async (userId: string) => {
  return await fetchf(`/api/users/${userId}/dashboard`, {
    cacheTime: 300, // Cache for 5 minutes
    staleTime: 60, // Background revalidate after 1 minute
    cacheKey: `user-dashboard-${userId}`, // Custom cache key
    skipCache: (response) => response.status === 503, // Skip caching on service unavailable
    refetchOnFocus: true, // Refresh when user returns to tab
  });
};

// Example: Optimistic updates with cache mutations
const updateUserProfile = async (userId: string, updates: any) => {
  // Optimistically update cache
  const currentData = await fetchf(`/api/users/${userId}`);
  await mutate(`/api/users/${userId}`, { ...currentData.data, ...updates });

  try {
    // Make actual API call
    const response = await fetchf(`/api/users/${userId}`, {
      method: 'PATCH',
      body: updates,
    });

    // Update cache with real response
    await mutate(`/api/users/${userId}`, response.data, { revalidate: true });

    return response;
  } catch (error) {
    // Revert cache on error
    await mutate(`/api/users/${userId}`, currentData.data);
    throw error;
  }
};

// Example: Cache invalidation after user logout
const logout = async () => {
  await fetchf('/api/auth/logout', { method: 'POST' });

  // Clear all user-related cache
  deleteCache('/api/user*');
  deleteCache('/api/dashboard*');
};

Real-time Polling Implementation

Click to expand

import { fetchf } from 'fetchff';

// Example: Job status monitoring with intelligent polling
const monitorJobStatus = async (jobId: string) => {
  return await fetchf(`/api/jobs/${jobId}/status`, {
    pollingInterval: 2000, // Poll every 2 seconds
    pollingDelay: 500, // Wait 500ms before first poll
    maxPollingAttempts: 30, // Max 30 attempts (1 minute total)

    shouldStopPolling(response, attempt) {
      // Stop polling when job is complete or failed
      if (
        response.data?.status === 'completed' ||
        response.data?.status === 'failed'
      ) {
        return true;
      }

      // Stop if we've been polling for too long
      if (attempt >= 30) {
        console.warn('Job monitoring timeout after 30 attempts');
        return true;
      }

      return false;
    },

    onResponse(response) {
      console.log(`Job ${jobId} status:`, response.data?.status);

      // Update UI progress if available
      if (response.data?.progress) {
        updateProgressBar(response.data.progress);
      }
    },
  });
};

// Example: Server health monitoring
const monitorServerHealth = async () => {
  return await fetchf('/api/health', {
    pollingInterval: 30000, // Check every 30 seconds
    shouldStopPolling(response, attempt) {
      // Never stop health monitoring (until manually cancelled)
      return false;
    },

    onResponse(response) {
      const isHealthy = response.data?.status === 'healthy';
      updateHealthIndicator(isHealthy);

      if (!isHealthy) {
        console.warn('Server health check failed:', response.data);
        notifyAdmins(response.data);
      }
    },

    onError(error) {
      console.error('Health check failed:', error.message);
      updateHealthIndicator(false);
    },
  });
};

// Helper functions (implementation depends on your UI framework)
function updateProgressBar(progress: number) {
  // Update progress bar in UI
  console.log(`Progress: ${progress}%`);
}

function updateHealthIndicator(isHealthy: boolean) {
  // Update health indicator in UI
  console.log(`Server status: ${isHealthy ? 'Healthy' : 'Unhealthy'}`);
}

function notifyAdmins(healthData: any) {
  // Send notifications to administrators
  console.log('Notifying admins about health issue:', healthData);
}

Using with React Query

Click to expand

Integrate fetchff with React Query to streamline your data fetching:

Note: Official support for useFetcher(url, config) is here. Check React Integration section above to get an idea how to use it instead of SWR.

import { createApiFetcher } from 'fetchff';
import { useQuery } from '@tanstack/react-query';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    getProfile: {
      url: '/profile/:id',
    },
  },
});

export const useProfile = (id: string) => {
  return useQuery({
    queryKey: ['profile', id],
    queryFn: () => api.getProfile({ urlPathParams: { id } }),
    enabled: !!id, // Only fetch when id exists
  });
};

Using with SWR

Click to expand

Combine fetchff with SWR for efficient data fetching and caching.

Note: Official support for useFetcher(url, config) is here. Check React Integration section above to get an idea how to use it instead of SWR.

Single calls:

import { fetchf } from 'fetchff';
import useSWR from 'swr';

const fetchProfile = (id: string) =>
  fetchf(`https://example.com/api/profile/${id}`, {
    strategy: 'softFail',
  });

export const useProfile = (id: string) => {
  const { data, error } = useSWR(id ? ['profile', id] : null, () =>
    fetchProfile(id),
  );

  return {
    profile: data?.data,
    isLoading: !error && !data,
    isError: error || data?.error,
  };
};

Many endpoints:

import { createApiFetcher } from 'fetchff';
import useSWR from 'swr';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  endpoints: {
    getProfile: {
      url: '/profile/:id',
    },
  },
});

export const useProfile = (id: string) => {
  const { data, error } = useSWR(id ? ['profile', id] : null, () =>
    api.getProfile({ urlPathParams: { id } }),
  );

  return {
    profile: data?.data,
    isLoading: !error && !data,
    isError: error || data?.error,
  };
};

🌊 Using with Vue

Click to expand

// src/api.ts
import { createApiFetcher } from 'fetchff';

const api = createApiFetcher({
  baseURL: 'https://example.com/api',
  strategy: 'softFail',
  endpoints: {
    getProfile: { url: '/profile/:id' },
  },
});

export default api;

// src/composables/useProfile.ts
import { ref, onMounted } from 'vue';
import api from '../api';

export function useProfile(id: number) {
  const profile = ref(null);
  const isLoading = ref(true);
  const isError = ref(null);

  const fetchProfile = async () => {
    const { data, error } = await api.getProfile({ urlPathParams: { id } });

    if (error) isError.value = error;
    else if (data) profile.value = data;

    isLoading.value = false;
  };

  onMounted(fetchProfile);

  return { profile, isLoading, isError };
}

<!-- src/components/Profile.vue -->
<template>
  <div>
    <h1>Profile</h1>
    <div v-if="isLoading">Loading...</div>
    <div v-if="isError">Error: {{ isError.message }}</div>
    <div v-if="profile">
      <p>Name: {{ profile.name }}</p>
      <p>Email: {{ profile.email }}</p>
    </div>
  </div>
</template>

<script lang="ts">
  import { defineComponent } from 'vue';
  import { useProfile } from '../composables/useProfile';

  export default defineComponent({
    props: { id: Number },
    setup(props) {
      return useProfile(props.id);
    },
  });
</script>

🛠️ Compatibility and Polyfills

Click to expand

Compatibility

While fetchff is designed to work seamlessly with modern environments (ES2018+), some older browsers or specific edge cases might require additional support.

Currently, fetchff offers three types of builds:

1. Browser ESM build (.mjs): Ideal for modern browsers and module-based environments (when you use the type="module" attribute). Location: dist/browser/index.mjs Compatibility: ES2018+

2. Standard Browser build: A global UMD bundle, compatible with older browsers. Location: dist/browser/index.global.js Compatibility: ES2018+

3. Node.js CJS build: Designed for Node.js environments that rely on CommonJS modules. Location: dist/node/index.js Compatibility: Node.js 18+

For projects that need to support older browsers, especially those predating ES2018, additional polyfills or transpilation may be necessary. Consider using tools like Babel, SWC or core-js to ensure compatibility with environments that do not natively support ES2018+ features. Bundlers like Webpack or Rollup usually handle these concerns out of the box.

You can check Can I Use ES2018 to verify browser support for specific ES2018 features.

Polyfills

For environments that do not support modern JavaScript features or APIs, you might need to include polyfills. Some common polyfills include:

• Fetch Polyfill: For environments that do not support the native fetch API. You can use libraries like whatwg-fetch to provide a fetch implementation.
• Promise Polyfill: For older browsers that do not support Promises. Libraries like es6-promise can be used.
• AbortController Polyfill: For environments that do not support the AbortController API used for aborting fetch requests. You can use the abort-controller polyfill.

Using node-fetch for Node.js < 18

If you need to support Node.js versions below 18 (not officially supported), you can use the node-fetch package to polyfill the fetch API. Install it with:

npm install node-fetch

Then, at the entry point of your application, add:

globalThis.fetch = require('node-fetch');

Note: Official support is for Node.js 18 and above. Using older Node.js versions is discouraged and may result in unexpected issues.

✔️ Support and collaboration

If you have any idea for an improvement, please file an issue. Feel free to make a PR if you are willing to collaborate on the project. Thank you :)