React.render and the Top Level React API

October 1, 2015 by Jim Sproch and Sebastian Markbåge

When you're in React's world you are just building components that fit into other components. Everything is a component. Unfortunately not everything around you is built using React. At the root of your tree you still have to write some plumbing code to connect the outer world into React.

The primary API for rendering into the DOM looks like this:

ReactDOM.render(reactElement, domContainerNode)

To update the properties of an existing component, you call render again with a new element.

If you are rendering React components within a single-page app, you may need to plug into the app's view lifecycle to ensure your app will invoke unmountComponentAtNode at the appropriate time. React will not automatically clean up a tree. You need to manually call:


This is important and often forgotten. Forgetting to call unmountComponentAtNode will cause your app to leak memory. There is no way for us to automatically detect when it is appropriate to do this work. Every system is different.

It is not unique to the DOM. If you want to insert a React Native view in the middle of an existing iOS app you will hit similar issues.

Helpers #

If you have multiple React roots, or a single root that gets deleted over time, we recommend that you always create your own wrapper API. These will all look slightly different depending on what your outer system looks like. For example, at Facebook we have a system that automatically ties into our page transition router to automatically call unmountComponentAtNode.

Rather than calling ReactDOM.render() directly everywhere, consider writing/using a library that will manage mounting and unmounting within your application.

In your environment you may want to always configure internationalization, routers, user data etc. If you have many different React roots it can be a pain to set up configuration nodes all over the place. By creating your own wrapper you can unify that configuration into one place.

Object Oriented Updates #

If you call ReactDOM.render a second time to update properties, all your props are completely replaced.

ReactDOM.render(<App locale="en-US" userID={1} />, container);
// props.userID == 1
// props.locale == "en-US"
ReactDOM.render(<App userID={2} />, container);
// props.userID == 2
// props.locale == undefined ??!?

In object-oriented programming, all state lives on each object instance and you apply changes incrementally by mutating that state, one piece at a time. If you are using React within an app that expects an object oriented API (for instance, if you are building a custom web component using React), it might be surprising/confusing to a user that setting a single property would wipe out all the other properties on your component.

We used to have a helper function called setProps which allowed you to update only a few properties at a time. Unfortunately this API lived on a component instance, required React to keep this state internally and wasn't very natural anyway. Therefore, we're deprecating it and suggest that you build it into your own wrapper instead.

Here's some boilerplate to get you started. It is a 0.14 migration path for codebases using setProps and replaceProps.

class ReactComponentRenderer {
  constructor(klass, container) {
    this.klass = klass;
    this.container = container;
    this.props = {};
    this.component = null;

  replaceProps(props, callback) {
    this.props = {};
    this.setProps(props, callback);

  setProps(partialProps, callback) {
    if (this.klass == null) {
        'setProps(...): Can only update a mounted or ' +
        'mounting component. This usually means you called setProps() on ' +
        'an unmounted component. This is a no-op.'
    Object.assign(this.props, partialProps);
    var element = React.createElement(this.klass, this.props);
    this.component = ReactDOM.render(element, this.container, callback);

  unmount() {
    this.klass = null;

Object-oriented APIs don't look like that though. They use setters and methods. I think we can do better. If you know more about the component API that you're rendering, you can create a more natural object-oriented API around your React component.

class ReactVideoPlayer {
  constructor(url, container) {
    this._container = container;
    this._url = url;
    this._isPlaying = false;

  _render() {
      <VideoPlayer url={this._url} playing={this._isPlaying} />,

  get url() {
    return this._url;

  set url(value) {
    this._url = value;

  play() {
    this._isPlaying = true;

  pause() {
    this._isPlaying = false;

  destroy() {

This example shows how to provide an imperative API on top of a declarative one. Similarly, the reverse can be done, and a declarative wrapper can be used when exposing a Web Component as a React component.

Community Round-up #27 – Relay Edition

September 14, 2015 by Steven Luscher

In the weeks following the open-source release of the Relay technical preview, the community has been abuzz with activity. We are honored to have been able to enjoy a steady stream of ideas and contributions from such a talented group of individuals. Let's take a look at some of the things we've achieved, together!

Teaching servers to speak GraphQL #

Every great Relay app starts by finding a GraphQL server to talk to. The community has spent the past few weeks teaching GraphQL to a few backend systems.

Bryan Goldstein (brysgo) has built a tool to help you define a GraphQL schema that wraps a set of Bookshelf.JS models. Check out graphql-bookshelf.

RisingStack (risingstack) created a GraphQL ORM called graffiti that you can plug into mongoose and serve using Express, Hapi, or Koa.

David Mongeau-Petitpas (dmongeau) is working on a way to vend your Laravel models through a GraphQL endpoint, laravel-graphql.

Gerald Monaco (devknoll) created graphql-schema to allow the creation of JavaScript GraphQL schemas using a fluent/chainable interface.

Jason Dusek (solidsnack) dove deep into PostgreSQL to teach it how to respond to GraphQL query strings as though they were SQL queries. Check out GraphpostgresQL.

Espen Hovlandsdal (rexxars) built a sql-to-graphql tool that can perform introspection on the tables of a MySQL or PostgreSQL database, and produce a queryable HTTP GraphQL endpoint out of it.

Mick Hansen (mickhansen) offers a set of schema-building helpers for use with the Sequelize ORM for MySQL, PostgreSQL, SQLite, and MSSQL.

GraphQL beyond JavaScript #

Robert Mosolgo (rmosolgo) brought the full set of schema-building and query execution tools to Ruby, in the form of graphql-ruby and graphql-relay-ruby. Check out his Rails-based demo.

Andreas Marek (andimarek) has brewed up a Java implementation of GraphQL, graphql-java.

vladar is hard at work on a PHP port of the GraphQL reference implementation, graphql-php.

Taeho Kim (dittos) is bringing GraphQL to Python, with graphql-py.

Oleg Ilyenko (OlegIlyenko) made a beautiful and delicious-looking website for a Scala implementation of GraphQL, sangria.

Joe McBride (joemcbride) has an up-and-running example of GraphQL for .NET, graphql-dotnet.

Show me, don't tell me #

Interact with this visual tour of Relay's architecture by Sam Gwilym (sgwilym).

Relay for visual learners

Sam has already launched a product that leverages Relay's data-fetching, optimistic responses, pagination, and mutations – all atop a Ruby GraphQL server:

Prototyping in the browser #

I (steveluscher) whipped up a prototyping tool that you can use to hack on a schema and a React/Relay app, from the comfort of your browser. Thanks to Jimmy Jia (taion) for supplying the local-only network layer, relay-local-schema.

Skeletons in the closet #

Joseph Rollins (fortruce) created a hot-reloading, auto schema-regenerating, Relay skeleton that you can use to get up and running quickly.

Michael Hart (mhart) built a simple-relay-starter kit using Browserify.

Routing around #

Jimmy Jia (taion) and Gerald Monaco (devknoll) have been helping lost URLs find their way to Relay apps through their work on react-router-relay. Check out Christoph Pojer's (cpojer) blog post on the topic. Jimmy completed the Relay TodoMVC example with routing, which you can check out at taion/relay-todomvc.

Chen Hung-Tu (transedward) built a chat app atop the above mentioned router, with threaded conversations and pagination. Check it out at transedward/relay-chat.

In your words #

React v0.14 Release Candidate

September 10, 2015 by Ben Alpert

We’re happy to announce our first release candidate for React 0.14! We gave you a sneak peek in July at the upcoming changes but we’ve now stabilized the release more and we’d love for you to try it out before we release the final version.

Let us know if you run into any problems by filing issues on our GitHub repo.

Installation #

We recommend using React from npm and using a tool like browserify or webpack to build your code into a single package:

  • npm install --save react@0.14.0-rc1
  • npm install --save react-dom@0.14.0-rc1

Remember that by default, React runs extra checks and provides helpful warnings in development mode. When deploying your app, set the NODE_ENV environment variable to production to use the production build of React which does not include the development warnings and runs significantly faster.

If you can’t use npm yet, we also provide pre-built browser builds for your convenience:

These builds are also available in the react and react-dom packages on bower.

Changelog #

Major changes #

  • Two Packages: React and React DOM #

    As we look at packages like react-native, react-art, react-canvas, and react-three, it has become clear that the beauty and essence of React has nothing to do with browsers or the DOM.

    To make this more clear and to make it easier to build more environments that React can render to, we’re splitting the main react package into two: react and react-dom. This paves the way to writing components that can be shared between the web version of React and React Native. We don’t expect all the code in an app to be shared, but we want to be able to share the components that do behave the same across platforms.

    The react package contains React.createElement, .createClass, .Component, .PropTypes, .Children, and the other helpers related to elements and component classes. We think of these as the isomorphic or universal helpers that you need to build components.

    The react-dom package has ReactDOM.render, .unmountComponentAtNode, and .findDOMNode. In react-dom/server we have server-side rendering support with ReactDOMServer.renderToString and .renderToStaticMarkup.

    var React = require('react');
    var ReactDOM = require('react-dom');
    var MyComponent = React.createClass({
      render: function() {
        return <div>Hello World</div>;
    ReactDOM.render(<MyComponent />, node);

    We’ve published the automated codemod script we used at Facebook to help you with this transition.

    The add-ons have moved to separate packages as well: react-addons-clone-with-props, react-addons-create-fragment, react-addons-css-transition-group, react-addons-linked-state-mixin, react-addons-perf, react-addons-pure-render-mixin, react-addons-shallow-compare, react-addons-test-utils, react-addons-transition-group, and react-addons-update, plus ReactDOM.unstable_batchedUpdates in react-dom.

    For now, please use matching versions of react and react-dom in your apps to avoid versioning problems.

  • DOM node refs #

    The other big change we’re making in this release is exposing refs to DOM components as the DOM node itself. That means: we looked at what you can do with a ref to a React DOM component and realized that the only useful thing you can do with it is call this.refs.giraffe.getDOMNode() to get the underlying DOM node. In this release, this.refs.giraffe is the actual DOM node. Note that refs to custom (user-defined) components work exactly as before; only the built-in DOM components are affected by this change.

    var Zoo = React.createClass({
      render: function() {
        return <div>Giraffe name: <input ref="giraffe" /></div>;
      showName: function() {
        // Previously: var input = this.refs.giraffe.getDOMNode();
        var input = this.refs.giraffe;

    This change also applies to the return result of ReactDOM.render when passing a DOM node as the top component. As with refs, this change does not affect custom components. With these changes, we’re deprecating .getDOMNode() and replacing it with ReactDOM.findDOMNode (see below).

  • Stateless function components #

    In idiomatic React code, most of the components you write will be stateless, simply composing other components. We’re introducing a new, simpler syntax for these components where you can take props as an argument and return the element you want to render:

    // Using an ES2015 (ES6) arrow function:
    var Aquarium = (props) => {
      var fish = getFish(props.species);
      return <Tank>{fish}</Tank>;
    // Or with destructuring and an implicit return, simply:
    var Aquarium = ({species}) => (
    // Then use: <Aquarium species="rainbowfish" />

    This pattern is designed to encourage the creation of these simple components that should comprise large portions of your apps. In the future, we’ll also be able to make performance optimizations specific to these components by avoiding unnecessary checks and memory allocations.

  • Deprecation of react-tools #

    The react-tools package and JSXTransformer.js browser file have been deprecated. You can continue using version 0.13.3 of both, but we no longer support them and recommend migrating to Babel, which has built-in support for React and JSX.

  • Compiler optimizations #

    React now supports two compiler optimizations that can be enabled in Babel 5.8.23 and newer. Both of these transforms should be enabled only in production (e.g., just before minifying your code) because although they improve runtime performance, they make warning messages more cryptic and skip important checks that happen in development mode, including propTypes.

    Inlining React elements: The optimisation.react.inlineElements transform converts JSX elements to object literals like {type: 'div', props: ...} instead of calls to React.createElement.

    Constant hoisting for React elements: The optimisation.react.constantElements transform hoists element creation to the top level for subtrees that are fully static, which reduces calls to React.createElement and the resulting allocations. More importantly, it tells React that the subtree hasn’t changed so React can completely skip it when reconciling.

Breaking changes #

As always, we have a few breaking changes in this release. Whenever we make large changes, we warn for at least one release so you have time to update your code. The Facebook codebase has over 15,000 React components, so on the React team, we always try to minimize the pain of breaking changes.

These three breaking changes had a warning in 0.13, so you shouldn’t have to do anything if your code is already free of warnings:

  • The props object is now frozen, so mutating props after creating a component element is no longer supported. In most cases, React.cloneElement should be used instead. This change makes your components easier to reason about and enables the compiler optimizations mentioned above.
  • Plain objects are no longer supported as React children; arrays should be used instead. You can use the createFragment helper to migrate, which now returns an array.
  • Add-Ons: classSet has been removed. Use classnames instead.

And these two changes did not warn in 0.13 but should be easy to find and clean up:

  • React.initializeTouchEvents is no longer necessary and has been removed completely. Touch events now work automatically.
  • Add-Ons: Due to the DOM node refs change mentioned above, TestUtils.findAllInRenderedTree and related helpers are no longer able to take a DOM component, only a custom component.

New deprecations, introduced with a warning #

  • Due to the DOM node refs change mentioned above, this.getDOMNode() is now deprecated and ReactDOM.findDOMNode(this) can be used instead. Note that in most cases, calling findDOMNode is now unnecessary – see the example above in the “DOM node refs” section.

    If you have a large codebase, you can use our automated codemod script to change your code automatically.

  • setProps and replaceProps are now deprecated. Instead, call ReactDOM.render again at the top level with the new props.

  • ES6 component classes must now extend React.Component in order to enable stateless function components. The ES3 module pattern will continue to work.

  • Reusing and mutating a style object between renders has been deprecated. This mirrors our change to freeze the props object.

  • Add-Ons: cloneWithProps is now deprecated. Use React.cloneElement instead (unlike cloneWithProps, cloneElement does not merge className or style automatically; you can merge them manually if needed).

  • Add-Ons: To improve reliability, CSSTransitionGroup will no longer listen to transition events. Instead, you should specify transition durations manually using props such as transitionEnterTimeout={500}.

Notable enhancements #

  • Added React.Children.toArray which takes a nested children object and returns a flat array with keys assigned to each child. This helper makes it easier to manipulate collections of children in your render methods, especially if you want to reorder or slice this.props.children before passing it down. In addition, now returns plain arrays too.
  • React uses console.error instead of console.warn for warnings so that browsers show a full stack trace in the console. (Our warnings appear when you use patterns that will break in future releases and for code that is likely to behave unexpectedly, so we do consider our warnings to be “must-fix” errors.)
  • Previously, including untrusted objects as React children could result in an XSS security vulnerability. This problem should be avoided by properly validating input at the application layer and by never passing untrusted objects around your application code. As an additional layer of protection, React now tags elements with a specific ES2015 (ES6) Symbol in browsers that support it, in order to ensure that React never considers untrusted JSON to be a valid element. If this extra security protection is important to you, you should add a Symbol polyfill for older browsers, such as the one included by Babel’s polyfill.
  • When possible, React DOM now generates XHTML-compatible markup.
  • React DOM now supports these standard HTML attributes: capture, challenge, inputMode, is, keyParams, keyType, minLength, summary, wrap. It also now supports these non-standard attributes: autoSave, results, security.
  • React DOM now supports these SVG attributes, which render into namespaced attributes: xlinkActuate, xlinkArcrole, xlinkHref, xlinkRole, xlinkShow, xlinkTitle, xlinkType, xmlBase, xmlLang, xmlSpace.
  • The image SVG tag is now supported by React DOM.
  • In React DOM, arbitrary attributes are supported on custom elements (those with a hyphen in the tag name or an is="..." attribute).
  • React DOM now supports these media events on audio and video tags: onAbort, onCanPlay, onCanPlayThrough, onDurationChange, onEmptied, onEncrypted, onEnded, onError, onLoadedData, onLoadedMetadata, onLoadStart, onPause, onPlay, onPlaying, onProgress, onRateChange, onSeeked, onSeeking, onStalled, onSuspend, onTimeUpdate, onVolumeChange, onWaiting.
  • Many small performance improvements have been made.
  • Many warnings show more context than before.
  • Add-Ons: A shallowCompare add-on has been added as a migration path for PureRenderMixin in ES6 classes.
  • Add-Ons: CSSTransitionGroup can now use custom class names instead of appending -enter-active or similar to the transition name.

New helpful warnings #

  • React DOM now warns you when nesting HTML elements invalidly, which helps you avoid surprising errors during updates.
  • Passing document.body directly as the container to ReactDOM.render now gives a warning as doing so can cause problems with browser extensions that modify the DOM.
  • Using multiple instances of React together is not supported, so we now warn when we detect this case to help you avoid running into the resulting problems.

Notable bug fixes #

  • Click events are handled by React DOM more reliably in mobile browsers, particularly in Mobile Safari.
  • SVG elements are created with the correct namespace in more cases.
  • React DOM now renders <option> elements with multiple text children properly and renders <select> elements on the server with the correct option selected.
  • When two separate copies of React add nodes to the same document (including when a browser extension uses React), React DOM tries harder not to throw exceptions during event handling.
  • Using non-lowercase HTML tag names in React DOM (e.g., React.createElement('DIV')) no longer causes problems, though we continue to recommend lowercase for consistency with the JSX tag name convention (lowercase names refer to built-in components, capitalized names refer to custom components).
  • React DOM understands that these CSS properties are unitless and does not append “px” to their values: animationIterationCount, boxOrdinalGroup, flexOrder, tabSize, stopOpacity.
  • Add-Ons: When using the test utils, Simulate.mouseEnter and Simulate.mouseLeave now work.
  • Add-Ons: ReactTransitionGroup now correctly handles multiple nodes being removed simultaneously.

New React Developer Tools

September 2, 2015 by Ben Alpert

A month ago, we posted a beta of the new React developer tools. Today, we're releasing the first stable version of the new devtools. We're calling it version 0.14, but it's a full rewrite so we think of it more like a 2.0 release.

Video/screenshot of new devtools

It contains a handful of new features, including:

  • Built entirely with React, making it easier to develop and extend
  • Firefox support
  • Selected component instance is available as $r from the console
  • More detail is shown in props in the component tree
  • Right-click any node and choose "Show Source" to jump to the render method in the Sources panel
  • Right-click any props or state value to make it available as $tmp from the console
  • Full React Native support

Installation #

Download the new devtools from the Chrome Web Store and on Mozilla Add-ons for Firefox. If you're developing using React, we highly recommend installing these devtools.

If you already have the Chrome extension installed, it should autoupdate within the next week. You can also head to chrome://extensions and click "Update extensions now" if you'd like to get the new version today. If you installed the devtools beta, please remove it and switch back to the version from the store to make sure you always get the latest updates and bug fixes.

If you run into any issues, please post them on our react-devtools GitHub repo.

ReactEurope Round-up

August 13, 2015 by Matthew Johnston

Last month, the first React.js European conference took place in the city of Paris, at ReactEurope. Attendees were treated to a range of talks covering React, React Native, Flux, Relay, and GraphQL. Big thanks to everyone involved with organizing the conference, to all the attendees, and everyone who gave their time to speak - it wouldn't have been possible without the help and support of the React community.

Christopher Chedeau gave the opening keynote to the conference:

Spencer Ahrens walks through building an advanced gestural UI leveraging the unique power of the React Native layout and animation systems to build a complex and fluid experience:

Lee Byron explores GraphQL, its core principles, how it works, and what makes it a powerful tool:

Joseph Savona explores the problems Relay solves, its architecture and the query lifecycle, and how can you use Relay to build more scalable apps. There are examples of how Relay powers applications as complex as the Facebook News Feed:

Nick Schrock and Dan Schafer take a deeper dive into putting GraphQL to work. How can we build a GraphQL API to work with an existing REST API or server-side data model? What are best practices when building a GraphQL API, and how do they differ from traditional REST best practices? How does Facebook use GraphQL? Most importantly, what does a complete and coherent GraphQL API looks like, and how can we get started building one?

Sebastian Markbåge talks about why the DOM is flawed and how it is becoming a second-class citizen in the land of React apps:

Sebastian McKenzie goes over how existing JSX build pipeline infrastructure can be further utilised to perform even more significant code transformations such as transpilation, optimisation, profiling and more, reducing bugs, making your code faster and you as a developer more productive and happy:

Cheng Lou gives a talk on the past, the present and the future of animation, and the place React can potentially take in this:

And there was a Q&A session with the whole team covering a range of React topics:

And there were lots of great talks from the React community:

  • Michael Chan looks at how to solve problems like CSS theming and media queries with contexts and plain old JavaScript. He also looks at the role of container-components and when it's better to "just use CSS.".
  • Elie Rotenberg talks about Flux over the Wire, building isomorphic, real-time React apps using a novel interpretation of Flux.
  • Ryan Florence says “Your front and back ends are already successfully in production but you don't have to miss out on the productivity that React brings. Forget the rewrites, this is brownfield!”.
  • Dan Abramov demonstrates how React can be used together with Webpack Hot Module Replacement to create a live editing environment with time travel that supercharges your debugging experience and transforms the way you work on real apps every day.
  • Mikhail Davydov shows you how to ask the browser layout engine for help, how to avoid slavery of DSL, and build declarative Text UI using only web-technologies like HTML, JS, CSS and React.
  • Kevin Robinson shares how user experience choices are a primary influence on how Twitter design the data layer, especially for teams developing new products with full-stack capabilities.
  • Jed Watson shares what Thinkmill have learned about React and mobile app development, and how they've approached the unique challenges of mobile web apps - with tools that are useful to all developers building touch interfaces with React, as well as a walkthrough of their development process and framework.
  • Michael Jackson discusses how your users can benefit from the many tools that React Router provides including server-side rendering, real URLs on native devices, and much, much more.
  • Michael Ridgway walks you through an isomorphic Flux architecture to give you the holy grail of frontend development.
  • Aria Buckles covers Khan Academy's techniques and patterns to make dealing with large pure components simpler, as well as current open questions.
  • Evan Morikawa and Ben Gotow talk about specific features of React & Flux, React CSS, programming design patterns, and custom libraries, which can turn a static application into a dynamic platform that an ecosystem of developers can build on top of.
  • Zalando,, Automattic, Thinkmill, and Red Badger provided lots of insight into how larger companies are using React.

There was also a great series of Lightning talks from Joshua Sierles, Ovidiu Cherecheș, Mike Grabowski, Dave Brotherstone, Sunil Pai, Andreas Savvides, and Petr Bela.

You can view the full list of talks on the ReactEurope YouTube channel.