Redux DevTools

A live-editing time travel environment for Redux.
See Dan's React Europe talk demoing it!

Features

• Lets you inspect every state and action payload
• Lets you go back in time by “cancelling” actions
• If you change the reducer code, each “staged” action will be re-evaluated
• If the reducers throw, you will see during which action this happened, and what the error was
• With persistState() store enhancer, you can persist debug sessions across page reloads

Overview

Redux DevTools is a development time package that provides power-ups for your Redux development workflow. Be careful to strip its code in production! To use Redux DevTools, you need to choose a “monitor”—a React component that will serve as a UI for the DevTools. Different tasks and workflows require different UIs, so Redux DevTools is built to be flexible in this regard. We recommend using LogMonitor for inspecting the state and time travel, and wrap it in a DockMonitor to quckly move it across the screen. That said, when you’re comfortable rolling up your own setup, feel free to do this, and share it with us.

Installation

npm install --save-dev redux-devtools

You’ll also likely want to install some monitors:

npm install --save-dev redux-devtools-log-monitor
npm install --save-dev redux-devtools-dock-monitor

Usage

Create a DevTools Component

Somewhere in your project, create a DevTools component by passing a monitor element to createDevTools. In the following example our monitor consists of LogMonitor docked within DockMonitor:

containers/DevTools.js

import React from 'react';

// Exported from redux-devtools
import { createDevTools } from 'redux-devtools';

// Monitors are separate packages, and you can make a custom one
import LogMonitor from 'redux-devtools-log-monitor';
import DockMonitor from 'redux-devtools-dock-monitor';

// createDevTools takes a monitor and produces a DevTools component
const DevTools = createDevTools(
  // Monitors are individually adjustable with props
  // Consult their repositories to learn about those props
  <DockMonitor toggleVisibilityKey='ctrl-h'
               changePositionKey='ctrl-q'>
    <LogMonitor theme='tomorrow' />
  </DockMonitor>
);

export default DevTools;

Note that you can use LogMonitor directly without wrapping it in DockMonitor if you’d like to display the DevTools UI somewhere right inside your application:

// If you'd rather not use docking UI, use <LogMonitor> directly
const DevTools = createDevTools(
  <LogMonitor theme='solarized' />
);

Use DevTools.instrument() Store Enhancer

The DevTools component you created with createDevTools() has a special static method called instrument(). It returns a store enhancer that you need to use in development.

A store enhancer is a function that takes createStore and returns an enhanced version of it that you will use instead. You probably already used another store enhancer—applyMiddleware(). Unlike applyMiddleware(), you will need to be careful to only use DevTools.instrument() in development environment, and never in production.

The easiest way to apply several store enhancers in a row is to use the compose() utility function that ships with Redux. It is the same compose() that you can find in Underscore and Lodash. In our case, we would use it to compose several store enhancers into one: compose(applyMiddleware(m1, m2, m3), DevTools.instrument()).

It’s important that you should add DevTools.instrument() after applyMiddleware in your compose() function arguments. This is because applyMiddleware is potentially asynchronous, but DevTools.instrument() expects all actions to be plain objects rather than actions interpreted by asynchronous middleware such as redux-promise or redux-thunk. So make sure applyMiddleware() goes first in the compose() call, and DevTools.instrument() goes after it.

If you’d like, you may add another store enhancer called persistState(). It ships with this package, and it lets you serialize whole sessions (including all dispatched actions and the state of the monitors) by a URL key. So if you visit http://localhost:3000/?debug_session=reproducing_weird_bug, do something in the app, then open http://localhost:3000/?debug_session=some_other_feature, and then go back to http://localhost:3000/?debug_session=reproducing_weird_bug, the state will be restored. The implementation of persistState() is fairly naïve but you can take it as an inspiration and build a proper UI for it if you feel like it!

Exclude DevTools from Production Builds

Finally, to make sure we’re not pulling any DevTools-related code in the production builds, we will envify our code. With Webpack, you can use DefinePlugin (Browserify equivalent is called envify) to turn magic constants like process.env.NODE_ENV into 'production' or 'development' strings depending on the environment, and import and render redux-devtools conditionally when process.env.NODE_ENV is not 'production'. Then, if you have an Uglify step before production, Uglify will eliminate dead if (false) branches with redux-devtools imports.

If you are using ES6 modules with Webpack 1.x and Babel, you might try putting your import statement inside an if (process.env.NODE_ENV !== 'production) to exclude the DevTools package from your production bundle. However this ES6 specification forbids it, so this won’t compile. Instead, you can use a conditional CommonJS require. Babel will let it compile, and Uglify will eliminate the dead branches before Webpack creates a bundle. This is why we recommend creating a configureStore.js file that either directs you to configureStore.dev.js or configureStore.prod.js depending on the configuration. While it is a little bit more maintenance, the upside is that you can be sure you won’t pull any development dependencies into the production builds, and that you can easily enable different middleware (e.g. crash reporting, logging) in the production environment.

store/configureStore.js

// Use ProvidePlugin (Webpack) or loose-envify (Browserify)
// together with Uglify to strip the dev branch in prod build.
if (process.env.NODE_ENV === 'production') {
  module.exports = require('./configureStore.prod');
} else {
  module.exports = require('./configureStore.dev');
}

store/configureStore.prod.js

import { createStore, applyMiddleware, compose } from 'redux';
import rootReducer from '../reducers';

const finalCreateStore = compose(
  // Middleware you want to use in production:
  applyMiddleware(p1, p2, p3),
  // Other store enhancers if you use any
)(createStore);

export default function configureStore(initialState) {
  return finalCreateStore(rootReducer, initialState);
};

store/configureStore.dev.js

import { createStore, applyMiddleware, compose } from 'redux';
import { persistState } from 'redux-devtools';
import rootReducer from '../reducers';
import DevTools from '../containers/DevTools';

const finalCreateStore = compose(
  // Middleware you want to use in development:
  applyMiddleware(d1, d2, d3),
  // Required! Enable Redux DevTools with the monitors you chose
  DevTools.instrument(),
  // Optional. Lets you write ?debug_session=<key> in address bar to persist debug sessions
  persistState(getDebugSessionKey())
)(createStore);

function getDebugSessionKey() {
  // You can write custom logic here!
  // By default we try to read the key from ?debug_session=<key> in the address bar
  const matches = window.location.href.match(/[?&]debug_session=([^&]+)\b/);
  return (matches && matches.length > 0)? matches[1] : null;
}

export default function configureStore(initialState) {
  const store = finalCreateStore(rootReducer, initialState);

  // Hot reload reducers (requires Webpack or Browserify HMR to be enabled)
  if (module.hot) {
    module.hot.accept('../reducers', () =>
      store.replaceReducer(require('../reducers')/*.default if you use Babel 6+ */)
    );
  }

  return store;
}

Render <DevTools> in Your App...

Finally, include the DevTools component in your page.
A naïve way to do this would be to render it right in your index.js:

index.js

import React from 'react';
import { render } from 'react-dom';
import { Provider } from 'react-redux';
import configureStore from './store/configureStore';
import TodoApp from './containers/TodoApp';

// Don't do this! You’re bringing DevTools into the production bundle.
import DevTools from './containers/DevTools';

const store = configureStore();

render(
  <Provider store={store}>
    <div>
      <TodoApp />
      <DevTools />
    </div>
  </Provider>
  document.getElementById('app')
);

We recommend a different approach. Create a Root.js component that renders the root of your application (usually some component surrounded by a <Provider>). Then use the same trick with conditional require statements to have two versions of it, one for development, and one for production:

containers/Root.js

if (process.env.NODE_ENV === 'production') {
  module.exports = require('./Root.prod');
} else {
  module.exports = require('./Root.dev');
}

containers/Root.dev.js

import React, { Component } from 'react';
import { Provider } from 'react-redux';
import TodoApp from './TodoApp';
import DevTools from './DevTools';

export default class Root extends Component {
  render() {
    const { store } = this.props;
    return (
      <Provider store={store}>
        <div>
          <TodoApp />
          <DevTools />
        </div>
      </Provider>
    );
  }
}

containers/Root.prod.js

import React, { Component } from 'react';
import { Provider } from 'react-redux';
import TodoApp from './TodoApp';

export default class Root extends Component {
  render() {
    const { store } = this.props;
    return (
      <Provider store={store}>
        <TodoApp />
      </Provider>
    );
  }
}

...Or Open Them in a New Window

When you use DockMonitor, you usually want to render <DevTools> at the root of your app. It will appear in a docked container above it. However, you can also render it anywhere else in your React component tree. In this case, you’d create a development and a production version of some other component that would either include or exclude <DevTools>.

For example (you don’t have to do that!), you may prefer to display the DevTools in a separate window instead of rendering it inside the page. In this case, you can remove DockMonitor from DevTools.js and just use the LogMonitor, and have some code like this:

index.js

import React from 'react';
import { Provider } from 'react-redux';
import { render } from 'react-dom';
import configureStore from './store/configureStore';
import App from './containers/App';

const store = configureStore();

render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById('root')
);

if (process.env.NODE_ENV !== 'production') {
  const showDevTools = require('./showDevTools');
  showDevTools(store);
}

showDevTools.js

import React from 'react';
import { render } from 'react-dom';
import DevTools from './containers/DevTools';

export default function showDevTools(store) {
  const popup = window.open(null, 'Redux DevTools', 'menubar=no,location=no,resizable=yes,scrollbars=no,status=no');
  // Reload in case it already exists
  popup.location.reload();
  
  setTimeout(() => {
    popup.document.write('<div id="react-devtools-root"></div>');
    render(
      <DevTools store={store} />,
      popup.document.getElementById('react-devtools-root')
    );
  }, 10);
}

Personal preferences vary, and whether to put the DevTools in a separate window, in a dock, or right inside you app’s user interface, is up to you. Make sure to check the documentation for the monitors you use and learn about the different props they support for customizing the appearance and the behavior.

Note that there are no useful props you can pass to the DevTools component other than the store. The store prop is needed if you don’t wrap <DevTools> in a <Provider>—just like with any connected component. To adjust the monitors, you need to pass props to them inside DevTools.js itself inside the createDevTools() call when they are used.

Gotchas

• Your reducers have to be pure and free of side effects to work correctly with DevTools. For example, even generating a random ID in reducer makes it impure and non-deterministic. Instead, do this in action creators.

• Make sure to only apply DevTools.instrument() and render <DevTools> in development! In production, this will be terribly slow because actions just accumulate forever. As described above, you need to use conditional requires and use ProvidePlugin (Webpack) or loose-envify (Browserify) together with Uglify to remove the dead code. Here is an example that adds Redux DevTools handling the production case correctly.

• It is important that DevTools.instrument() store enhancer should be added to your middleware stack after applyMiddleware in the composed functions, as applyMiddleware is potentially asynchronous. Otherwise, DevTools won’t see the raw actions emitted by asynchronous middleware such as redux-promise or redux-thunk.

Running Examples

Clone the project:

git clone https://github.com/gaearon/redux-devtools.git
cd redux-devtools

Run npm install in the root folder:

npm install

Now you can open an example folder and run npm install there:

cd examples/counter # or examples/todomvc
npm install

Finally, run the development server and open the page:

npm start
open http://localhost:3000

Try clicking on actions in the log, or changing some code inside the reducers. You should see the action log re-evaluate the state on every code change.

Also try opening http://localhost:3000/?debug_session=123, click around, and then refresh. You should see that all actions have been restored from the local storage.

Custom Monitors

DevTools accepts monitor components so you can build a completely custom UI. LogMonitor and DockMonitor are just examples of what is possible.

I challenge you to build a custom monitor for Redux DevTools!

Some crazy ideas for custom monitors:

• A slider that lets you jump between computed states just by dragging it
• An in-app layer that shows the last N states right in the app (e.g. for animation)
• A time machine like interface where the last N states of your app reside on different Z layers
• Feel free to come up with and implement your own! Check LogMonitor propTypes to see what you can do.

In fact some of these are implemented already:

redux-slider-monitor

Keep them coming!

Create a PR to add your custom monitor.

License

MIT