Install the store enhancer

import { createStore, compose, applyMiddleware } from 'redux';
import reducer from './reducers';
import { install } from 'redux-loop';
import someMiddleware from 'some-middleware';

const enhancer = compose(

const store = createStore(reducer, initialState, enhancer);

Installing redux-loop is as easy as installing any other store enhancer. You can apply it directly over createStore or compose it with other enhancers and middlewares. Composition of enhancers can be confusing, so the order in which install() is applied may matter. If something like applyMiddleware() doesn't work when called before install(), applying after may fix the issue.

Write a reducer with some cmd objects (side effects)

import { loop, Cmd } from 'redux-loop';

function initAction(){
    return {
      type: 'INIT'

function fetchUser(userId){
    return fetch(`/api/users/${userId}`);

function userFetchSuccessfulAction(user){
   return {

function userFetchFailedAction(err){
   return {
      type: 'USER_FETCH_ERROR',

const initialState = {
  initStarted: false,
  user: null,
  error: null

function reducer(state = initialState, action) {
  switch(action.type) {
  case 'INIT':
    return loop(
      {...state, initStarted: true},
      Cmd.run(fetchUser, {
        successActionCreator: userFetchSuccessfulAction,
        failActionCreator: userFetchFailedAction,
        args: ['123']

    return {...state, user: action.user};

    return {...state, error: action.error};

    return state;

Any reducer can return a loop instead of a state object. A loop joins an updated model state with a cmd for the store to process. A cmd is just an object that describes what side effect should run, and what to do with the result. There are several options for cmd objects, all available under the Cmd module:

  • run(functionToCall, options)
    • Accepts a function to run and options for how to call it and what to do with the result.
  • action(actionToDispatch)
    • Accepts an action to dispatch immediately once the current dispatch cycle is completed.
  • list(cmds, options)
    • Accepts an array of other cmd objects and runs them. Options control whether they run in parallel or in order, and when to dispatch the resulting actions.
  • map(cmd, higherOrderActionCreator, ...args)
    • Accepts a cmd and passes the resulting action(s) through higherOrderActionCreator to create a nested action, optionally passing extra args to higherOrderActionCreator before the nested action.
  • none
    • A no-op cmd, for convenience.

See detailed documentation about all of the available methods from the Cmd modules

combineReducers with redux-loop

The combineReducers implementation in redux-loop is aware that some of your reducers might return cmd objects, and it knows how to properly compose them and forward them to the store. Instead of using combineReducers from Redux itself, use the version from redux-loop instead

// Redux's combineReducers method does not know how to deal with cmd objects!
// import { createStore, combineReducers } from 'redux';

import { createStore } from 'redux';
import { combineReducers, install } from 'redux-loop';

import { firstReducer, secondReducer } from './reducers';

const reducer = combineReducers({
  first: firstReducer,
  second: secondReducer,

const store = createStore(reducer, initialState, install());

A note on TypeScript

TypeScript is fully supported by redux-loop. Here is an example project

Avoid circular loops!

function reducer(state, action) {
  switch (action.type) {
    case 'FIRST':
      return loop(

    case 'SECOND':
      return loop(

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