TypeScript FSA

A simple Action Creator library for TypeScript. Its goal is to provide simple yet type-safe experience with Flux actions. Created actions are FSA-compliant:

interface Action<P> {
  type: string;
  payload: P;
  error?: boolean;
  meta?: Object;
}

Installation

npm install --save typescript-fsa

Usage

Basic

import actionCreatorFactory from 'typescript-fsa';

const actionCreator = actionCreatorFactory();

// Specify payload shape as generic type argument.
const somethingHappened = actionCreator<{foo: string}>('SOMETHING_HAPPENED');

// Get action creator type.
console.log(somethingHappened.type);  // SOMETHING_HAPPENED

// Create action.
const action = somethingHappened({foo: 'bar'});
console.log(action);  // {type: 'SOMETHING_HAPPENED', payload: {foo: 'bar'}}

Async Action Creators

Async Action Creators are objects with properties started, done and failed whose values are action creators.

import actionCreatorFactory from 'typescript-fsa';

const actionCreator = actionCreatorFactory();

// specify parameters and result shapes as generic type arguments
const doSomething =
  actionCreator.async<{foo: string},   // parameter type
                      {bar: number},   // success type
                      {code: number}   // error type
                     >('DO_SOMETHING');

console.log(doSomething.started({foo: 'lol'}));
// {type: 'DO_SOMETHING_STARTED', payload: {foo: 'lol'}}

console.log(doSomething.done({
  params: {foo: 'lol'},
  result: {bar: 42},
});
// {type: 'DO_SOMETHING_DONE', payload: {
//   params: {foo: 'lol'},
//   result: {bar: 42},
// }}

console.log(doSomething.failed({
  params: {foo: 'lol'},
  error: {code: 42},
});
// {type: 'DO_SOMETHING_FAILED', payload: {
//   params: {foo: 'lol'},
//   error: {code: 42},
// }, error: true}

Actions With Type Prefix

You can specify a prefix that will be prepended to all action types. This is useful to namespace library actions as well as for large projects where it's convenient to keep actions near the component that dispatches them.

// MyComponent.actions.ts
import actionCreatorFactory from 'typescript-fsa';

const actionCreator = actionCreatorFactory('MyComponent');

const somethingHappened = actionCreator<{foo: string}>('SOMETHING_HAPPENED');

const action = somethingHappened({foo: 'bar'});
console.log(action);
// {type: 'MyComponent/SOMETHING_HAPPENED', payload: {foo: 'bar'}}

Redux

// actions.ts
import actionCreatorFactory from 'typescript-fsa';

const actionCreator = actionCreatorFactory();

export const somethingHappened =
  actionCreator<{foo: string}>('SOMETHING_HAPPENED');
export const somethingAsync =
  actionCreator.async<{foo: string},
                      {bar: string}
                     >('SOMETHING_ASYNC');


// reducer.ts
import {Action} from 'redux';
import {isType} from 'typescript-fsa';
import {somethingHappened, somethingAsync} from './actions';

type State = {bar: string};

export const reducer = (state: State, action: Action): State => {
  if (isType(action, somethingHappened)) {
    // action.payload is inferred as {foo: string};

    action.payload.bar;  // error

    return {bar: action.payload.foo};
  }

  if (isType(action, somethingAsync.started)) {
    return {bar: action.payload.foo};
  }

  if (isType(action, somethingAsync.done)) {
    return {bar: action.payload.result.bar};
  }

  return state;
};


// epic.ts
import {Action} from 'redux';
import {Observable} from 'rxjs';
import {somethingAsync} from './actions';

export const epic = (actions$: Observable<Action>) =>
  actions$.filter(somethingAsync.started.match)
    .delay(2000)
    .map(action => {
      // action.payload is inferred as {foo: string};

      action.payload.bar;  // error

      return somethingAsync.done({
        params: action.payload,
        result: {
          bar: 'bar',
        },
      });
    });

Companion packages

• typescript-fsa-redux-saga
• typescript-fsa-redux-observable
• typescript-fsa-redux-thunk
• typescript-fsa-reducers

Resources

• Type-safe Flux Standard Actions (FSA) in React Using TypeScript FSA
• Type-safe Asynchronous Actions (Redux Thunk) Using TypeScript FSA

API

actionCreatorFactory(prefix?: string, defaultIsError?: Predicate): ActionCreatorFactory

Creates Action Creator factory with optional prefix for action types.

• prefix?: string: Prefix to be prepended to action types.
• defaultIsError?: Predicate: Function that detects whether action is error given the payload. Default is payload => payload instanceof Error.

ActionCreatorFactory<P>(type: string, commonMeta?: object, isError?: boolean): ActionCreator<P>

Creates Action Creator that produces actions with given type and payload of type P.

• type: string: Type of created actions.
• commonMeta?: object: Metadata added to created actions.
• isError?: boolean: Defines whether created actions are error actions.

ActionCreatorFactory#async<P, S, E>(type: string, commonMeta?: object): AsyncActionCreators<P, S, E>

Creates three Action Creators: started, done and failed, useful to wrap asynchronous processes.

• type: string: Prefix for types of created actions, which will have types ${type}_STARTED, ${type}_DONE and ${type}_FAILED.
• commonMeta?: object: Metadata added to created actions.

ActionCreator(payload: P, meta?: object): Action<P>

Creates action with given payload and metadata.

• payload: P: Action payload.
• meta?: object: Action metadata. Merged with commonMeta of Action Creator.

isType(action: Action, actionCreator: ActionCreator): boolean

Returns true if action has the same type as action creator. Defines Type Guard that lets TypeScript know payload type inside blocks where isType returned true:

const somethingHappened = actionCreator<{foo: string}>('SOMETHING_HAPPENED');

if (isType(action, somethingHappened)) {
  // action.payload has type {foo: string};
}

ActionCreator#match(action: Action): boolean

Identical to isType except it is exposed as a bound method of an action creator. Since it is bound and takes a single argument it is ideal for passing to a filtering function like Array.prototype.filter or RxJS's Observable.prototype.filter.

const somethingHappened = actionCreator<{foo: string}>('SOMETHING_HAPPENED');
const somethingElseHappened =
  actionCreator<{bar: number}>('SOMETHING_ELSE_HAPPENED');

if (somethingHappened.match(action)) {
  // action.payload has type {foo: string};
}

const actionArray = [
  somethingHappened({foo: 'foo'}),
  somethingElseHappened({bar: 5}),
]

// somethingHappenedArray has inferred type Action<{foo: string}>[];
const somethingHappenedArray = actionArray.filter(somethingHappened.match)

For more on using Array.prototype.filter as a type guard, see this github issue.