redux-latch

A Redux library for restricting and synchronising action-creator execution

Overview

A common pattern in Redux is using flags to signal that an asynchronous action-creator is currently executing or has been executed, the flags are used to prevent action-creators running simultaneously or to prevent them from running multiple times. redux-latch provides a set of higher-order actions which enable you to handle these situations more declaratively.

As an example say you have an action-creator which you want to only run once after the user has logged in, it might look something like this:

function loadUserPermissions(username) {
   return (dispatch, getState) => {
      const userStore = getState().userStore;
       
      if (userStore.permissionsLoading || userStore.permissions)
         return;
         
      dispatch({ type: USER_PERMISSIONS_LOADING, payload: true });
      
      return fetchUserPermissions()
         .then(permissions => {
            dispatch({ type: SET_USER_PERMISSIONS, payload: permissions });
            dispatch({ type: USER_PERMISSIONS_LOADING, payload: false });
         })
   }
}

Using the createEnsure higher-order action provided by redux-latch you can remove the ad-hoc flags from the store, and simplify the action-creator so that it simply performs the fetch:

function loadUserPermissions(username) {
   return (dispatch, getState) => {      
      api.fetchUserPermissions()
         .then(permissions => {
            dispatch({ type: SET_USER_PERMISSIONS, payload: permissions });
         })
   }
}

Calling createEnsure on this action-creator will return a new action-creator which wraps the original and ensures that it is only ever executed once.

import { createEnsure } from 'redux-latch';
const ensureUserPermissions = createEnsure(loadUserPermissions);    

Then in your code, just use the ensureUserPermissions action-creator to trigger the fetch instead. redux-latch maintains all of its state inside the redux store, so isomorphism and time-travelling are both handled.

Usage

You need to initialise the latch reducer where redux-latch will hold its state, by default redux-latch will expect this to be located at state.latches, however this can be overridden.

import {latchReducer} from 'redux-latch';

const combined = combineReducers({
   latches: latchReducer,
   products: productReducer,
   users: userReducer
});

redux-latch also depends on the redux-thunk middleware being present.

Higher-Order Actions

createLatch

Will enhance the action-creator so that it is never called more than N times. You can also specify the number of concurrent exections allowed. The function returns a Latch object with an execute method to trigger the action-creator and an invalidate method to reset the latch.

function createLatch(actionCreator: ActionCreator, options?: LatchOptions): Latch;

interface Latch {
	execute: ActionCreator;
	invalidate: (...args) => void;
}

interface LatchOptions {
   displayName?: string;
   stateSelector?: (state: any) => LatchState;
   keySelector?: (...args) => any[];
   max?: number;
   maxConcurrent?: number;
}

createEnsure

Just returns the execute methods of the latch. Useful if you never want to call invalidate.