redux-when

Redux middleware for delaying dispatch of an action until a condition evaluates to true.

If you're upgrading from v0.1.x make sure you read about the changes introduced in v1.0.0.

Why

Usually, you use promises to chain asynchronous actions:

/*
 Save the form and navigate somewhere
 */
const handleFormSubmit = () => {
  Promise.resolve()
    .then(() => store.dispatch(save(data)))
    .then(() => store.dispatch(navigate()))
  ;
}

But sometimes asynchronous actions have already been dispatched and you don't have a promise to chain on. redux-when was created to solve this problem:

 
/*
 Save the form
 */
const handleFieldBlur = () => {
  store.dispatch(save(data))
};
 
/*
 Wait for any save actions to finish and then navigate somewhere
 */
const handleFormSubmit = () => {
  store.dispatch(once(state => state.saved, navigate()));
}
 

Installation

npm install --save redux-when

Usage

import {createStore, applyMiddleware} from 'redux';
import middleware, {once} from 'redux-when';
 
const reducer = (state = {}, action = {}) => {
  switch (action.type) {
 
    case 'SAVE':
      return {...state, saved: true};
 
    case 'NAVIGATE':
      return {...state, navigated: true};
 
    default:
      return state;
 
  }
};
 
//create the store
const store = createStore(reducer, {}, applyMiddleware(middleware));
 
//dispatch the `NAVIGATE` action ONCE the state has been saved
store.dispatch(once(state => state.saved, () => ({type: 'NAVIGATE'})));
 
//prints: {}
console.log(store.getState());
 
//dispatch the `SAVE` action which will update the state and trigger
// the delayed `NAVIGATE` action
store.dispatch({type: 'SAVE'});
 
//prints: {saved: true, navigated: true}
console.log(store.getState());
 

API

middleware

The Redux middleware.

once(condition, createAction)

Creates an action that will execute ONCE when the condition evaluates to true.

Parameters:

• condition : (state : object, action : object) => boolean — Required. The condition that determines when the action is dispatched.

• createAction : (action : object) => * — Required. A function creating the action that will be dispatched when the condition evaluates to true. Can return any value dispatchable by your store including thunks, promises etc as long as your store is configured with the necessary middleware.

Returns:

Returns a dispatchable Redux action that will be handled by the redux-when middleware. When dispatched, a cancel token will be returned.

Note: You MUST dispatch the action created by once() otherwise nothing will happen.

store.dispatch(once(() => true, () => {type: 'XYZ'}));

when(condition, createAction)

Creates an action that will execute EVERY time the condition evaluates to true.

Parameters:

• condition : (state : object, action : object) => boolean — Required. The condition that determines when the action is dispatched.

• createAction : (action : object) => * — Required. A function creating the action that will be dispatched when the condition evaluates to true. Can return any value dispatchable by your store including thunks, promises etc as long as your store is configured with the necessary middleware.

Returns:

Returns a dispatchable Redux action that will be handled by the redux-when middleware. When dispatched, a cancel token will be returned.

Note: You MUST dispatch the action created by when() otherwise nothing will happen.

store.dispatch(when(() => true, () => {type: 'XYZ'}));

cancel(token)

Cancels a delayed action created by once() or when().

Parameters:

• token : * — Required. A token returned by once() or when().

Returns:

Returns a dispatchable Redux action that will be handled by the redux-when middleware. When dispatched, null will be returned.

Note: You MUST dispatch the action created by cancel() otherwise nothing will happen.

import React from 'react';
import {connect} from 'react-redux';
 
class Example extends React.Component {
 
  componentWillMount() {
    this.token = this.props.dispatch(when(() => true, () => {type: 'XYZ'));
  }
 
  componentWillUnmount() {
    this.token = this.props.dispatch(cancel(this.token));
  }
 
}
 
export default connect()(Example);

Change log

Change log.