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Flux Standard Action

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Introduction

A human-friendly standard for Flux action objects. Feedback welcome.

Motivation

It's much easier to work with Flux actions if we can make certain assumptions about their shape. For example, essentially all Flux actions have an identifier field, such as type, actionType, or actionId. Many Flux implementations also include a way for actions to indicate success or failure, especially as the result of a data-fetching operation. Defining a minimal, common standard for these patterns enables the creation of useful tools and abstractions.

Errors as a first class concept

Flux actions can be thought of as an asynchronous sequence of values. It is important for asynchronous sequences to deal with errors. Currently, many Flux implementations don't do this, and instead define separate action types like LOAD_SUCCESS and LOAD_FAILURE. This is less than ideal, because it overloads two separate concerns: disambiguating actions of a certain type from the "global" action sequence, and indicating whether or not an action represents an error. FSA treats errors as a first class concept.

Design goals

  • Human-friendly. FSA actions should be easy to read and write by humans.
  • Useful. FSA actions should enable the creation of useful tools and abstractions.
  • Simple. FSA should be simple, straightforward, and flexible in its design.

Example

A basic Flux Standard Action:

{
  type: 'ADD_TODO',
  payload: {
    text: 'Do something.'  
  }
}

An FSA that represents an error, analogous to a rejected Promise:

{
  type: 'ADD_TODO',
  payload: new Error(),
  error: true
}

Actions

An action MUST

  • be a plain JavaScript object.
  • have a type property.

An action MAY

  • have an error property.
  • have a payload property.
  • have a meta property.

An action MUST NOT include properties other than type, payload, error, and meta.

type

The type of an action identifies to the consumer the nature of the action that has occurred. type is a string constant. If two types are the same, they MUST be strictly equivalent (using ===).

payload

The optional payload property MAY be any type of value. It represents the payload of the action. Any information about the action that is not the type or status of the action should be part of the payload field.

By convention, if error is true, the payload SHOULD be an error object. This is akin to rejecting a promise with an error object.

error

The optional error property MAY be set to true if the action represents an error.

An action whose error is true is analogous to a rejected Promise. By convention, the payload SHOULD be an error object.

If error has any other value besides true, including undefined and null, the action MUST NOT be interpreted as an error.

meta

The optional meta property MAY be any type of value. It is intended for any extra information that is not part of the payload.

Utility functions

The module flux-standard-action is available on npm. It exports a few utility functions.

isFSA(action)

import { isFSA } from 'flux-standard-action';

Returns true if action is FSA compliant.

isError(action)

import { isError } from 'flux-standard-action';

Returns true if action represents an error.

Libraries

  • redux-actions - a set of helpers for creating and handling FSA actions in Redux.
  • redux-promise - Redux promise middleware that supports FSA actions.
  • redux-rx - RxJS utilities for Redux, including a middleware that supports FSA actions.