metch-case

Metch is a TypeScript package that provides utility functions for branching and conditional execution based on patterns. It allows you to define multiple branches, evaluate an item against these branches, and execute the corresponding callbacks based on the matching branch.

Installation

You can install Metch using npm or yarn:

npm install metch

or

yarn add metch

Usage

To use Metch in your TypeScript project, import the desired functions from the package:

import { metch, metchReturn, DefaultBranch } from 'metch-case';

metch()

The metch function evaluates an item against a set of branches and executes the callback associated with the first matching branch. It follows a specific order of evaluation where the first matching branch is executed, and subsequent branches are ignored.

Syntax

metch<T>(item: T, branches: MatchBranches<T>, defaultBranch?: MetchBranchCallback<T>): void | Promise<void>

• item: The item to be evaluated against the branches.
• branches: An array of MatchBranch objects. Each MatchBranch is an array of 2 items:-
  • BranchJudge: will evaluate the item given. a judge can be a boolean, or a value of the same type as item, or a function that returns a boolean
  • BranchCallback: will execute if the judge allows it. Can be both async and sync.
• defaultBranch: Optional default branch if all other branches not matched.

Example

import {metch, DefaultBranch} from 'metch-case';
import fs from "fs/promises"

let filePath: string | undefined = 'notValid.txt';

await metch(filePath, [
    [undefined, async (file) => {
        console.log(await fs.readFile("undefined.txt", "utf-8"));
    }], 
    ['animal.txt', async (file) => {
        console.log(await fs.readFile(file!, "utf-8"))
    }], 
    [path => path!.includes('.txt'), async (file) => {
        console.log(await fs.readFile('data.txt', "utf-8"));
    }]
], async (item) => {
  // Optional Default branch 
  console.log(await fs.readFile('default.txt', 'utf-8'))
})

metchReturn()

The metchReturn function evaluates an item against a set of branches, executes the callback associated with the first matching branch, and returns a value. It follows the same evaluation order as metch, where the first matching branch is executed and subsequent branches are ignored.

If none of the branches match, the defaultBranch callback is executed.

Syntax

metchReturn<T, U>(item: T, branches: MatchReturnBranches<T, U>, defaultBranch: MatchReturnDefaultbranch<T, U>): U | Promise<U>

• item: The item to be evaluated against the branches.
• branches: An array of MatchReturnBranch objects. Each MatchReturnBranch consists of a branch judge or value, and a callback function to be executed if the judge or value matches the item.
• defaultBranch: The callback function to be executed if none of the branches match.

Example

import { metchReturn } from 'metch-case';
import fs from "fs/promises"

let filePath: string | undefined = 'animal.txt';

const fileData = await metchReturn(filePath, [
    [undefined, async (file) => {
        return await fs.readFile("undefined.txt", "utf-8");
    }], 
    ['animal.txt', async (file) => {
        return await fs.readFile(file!, "utf-8");
    }], 
    [path => path!.includes('.txt'), async (file) => {
        return await fs.readFile('data.txt', "utf-8");
    }],
], async (file) => {
    // Default Branch
    return await fs.readFile('default.txt', 'utf-8')
});

console.log(fileData);

Judge

Each branch inside metch() or metchReturn() has a judge. The item will be evaluated using this judge. If the judge allows it, then the callback inside that branch will be executed, and other branches will be ignored.

A judge<T> (Where T is the type of the item given) can be one of the following :-

• boolean
• (item: T) => boolean | undefined
• T
• Query<T>

boolean

Callback will be executed if judge is true.

Example

let filePath: string | undefined = 'animal.txt';

const fileData = await metchReturn(filePath, [
    [true, async (file) => {
        // Will always be executed and ignore other branches
        return await fs.readFile("always.txt", "utf-8");
    }]
], async (file) => {
    // Default Branch
    return await fs.readFile('default.txt', 'utf-8')
});

(item: T) => boolean | undefined

Callback will be executed if the result of the function is true.

Example

let filePath: string = 'animal.txt';

const fileData = await metchReturn(filePath, [
    [(file) => file.endsWith('.txt'), async (file) => {
        return await fs.readFile(file, "utf-8");
    }]
], async (file) => {
    // Default Branch
    return await fs.readFile('default.txt', 'utf-8')
});

T

Callback will be executed if the judge is strictly equal to item. In this case judge must be the same type as item.

Example

let filePath: string | undefined = 'animal.txt';

const fileData = await metchReturn(filePath, [
    [undefined, async () => {
      return await fs.readFile('undefined.txt', 'utf-8')
    }]
    [(file) => file!.endsWith('.txt'), async (file) => {
        return await fs.readFile(file, 'utf-8');
    }]
], async (file) => {
    // Default Branch
    return await fs.readFile('default.txt', 'utf-8')
});

Query<T>

Act as AND / OR operator for a branch's judge.

Example

const branches: MetchBranches<any> = [
     [Query.Or<any>(undefined, null, 1, (path: any) => typeof path !== 'string'), () => {
          console.log('value is not a valid string')
      }],
      [Query.And((path: any) => typeof path === 'string', 'animal'), (item) => {
          console.log('value is a string and animal')
      }],
 ];
 
 await metch('animal' as any, branches, (item) => {
      console.log('default branch')
 });

Note

It is recommended to pass the item's data type when using the Query.

let item: string | undefined = 'hello world';
Query.And<string | undefined>(...);
Query.Or<string | null>(...);