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React v15.0

April 7th, 2016

We would like to thank the React community for reporting issues and regressions in the release candidates on our issue tracker. Over the last few weeks we fixed those issues, and now, after two release candidates, we are excited to finally release the stable version of React 15. As a reminder, we’re switching to major versionn to indicate that we have been using React in production for a long time. This 15.0 release follows our previous 0.14 version and we’ll continue to follow semver like we’ve been doing since 2013. It’s also worth noting that we no longer actively support Internet Explorer 8. We believe React will work in its current form there but we will not be prioritizing any efforts to fix new issues that only affect IE8. React 15 brings significant improvements to how we interact with the DOM:
  • We are now using document.createElement instead of setting innerHTML when mounting components. This allows us to get rid of the data-reactid attribute on every node and make the DOM lighter. Using document.createElement is also faster in modern browsers and fixes a number of edge cases related to SVG elements and running multiple copies of React on the same page.
  • Historically our support for SVG has been incomplete, and many tags and attributes were missing. We heard you, and in React 15 we added support for all the SVG attributes that are recognized by today’s browsers. If we missed any of the attributes you’d like to use, please let us know. As a bonus, thanks to using document.createElement, we no longer need to maintain a list of SVG tags, so any SVG tags that were previously unsupported should work just fine in React 15.
  • We received some amazing contributions from the community in this release, and we would like to highlight this pull request by Michael Wiencek in particular. Thanks to Michael’s work, React 15 no longer emits extra <span> nodes around the text, making the DOM output much cleaner. This was a longstanding annoyance for React users so it’s exciting to accept this as an outside contribution.
While this isn’t directly related to the release, we understand that in order to receive more community contributions like Michael’s, we need to communicate our goals and priorities more openly, and review pull requests more decisively. As a first step towards this, we started publishing React core team weekly meeting notes again. We also intend to introduce an RFC process inspired by Ember RFCs so external contributors can have more insight and influence in the future development of React. We will keep you updated about this on our blog. We are also experimenting with a new changelog format in this post. Every change now links to the corresponding pull request and mentions the author. Let us know whether you find this useful!

Upgrade Guide #

As usual with major releases, React 15 will remove support for some of the patterns deprecated nine months ago in React 0.14. We know changes can be painful (the Facebook codebase has over 20,000 React components, and that’s not even counting React Native), so we always try to make changes gradually in order to minimize the pain. If your code is free of warnings when running under React 0.14, upgrading should be easy. The bulk of changes in this release are actually behind the scenes, impacting the way that React interacts with the DOM. The other substantial change is that React now supports the full range of SVG elements and attributes. Beyond that we have a large number of incremental improvements and additional warnings aimed to aid developers. We’ve also laid some groundwork in the core to bring you some new capabilities in future releases. See the changelog below for more details.

Installation #

We recommend using React from npm and using a tool like browserify or webpack to build your code into a single bundle. To install the two packages:
  • npm install --save react react-dom
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 provide pre-built browser builds for your convenience, which are also available in the react package on bower.

Changelog #

Major changes #

  • document.createElement is in and data-reactid is out #

    There were a number of large changes to our interactions with the DOM. One of the most noticeable changes is that we no longer set the data-reactid attribute for each DOM node. While this will make it more difficult to know if a website is using React, the advantage is that the DOM is much more lightweight. This change was made possible by us switching to use document.createElement on initial render. Previously we would generate a large string of HTML and then set node.innerHTML. At the time, this was decided to be faster than using document.createElement for the majority of cases and browsers that we supported. Browsers have continued to improve and so overwhelmingly this is no longer true. By using createElement we can make other parts of React faster. The ids were used to map back from events to the original React component, meaning we had to do a bunch of work on every event, even though we cached this data heavily. As we’ve all experienced, caching and in particularly invalidating caches, can be error prone and we saw many hard to reproduce issues over the years as a result. Now we can build up a direct mapping at render time since we already have a handle on the node. Note: data-reactid is still present for server-rendered content, however it is much smaller than before and is simply an auto-incrementing counter. @spicyj in #5205
  • No more extra <span>s #

    Another big change with our DOM interaction is how we render text blocks. Previously you may have noticed that React rendered a lot of extra <span>s. For example, in our most basic example on the home page we render <div>Hello {this.props.name}</div>, resulting in markup that contained 2 <span>s. Now we’ll render plain text nodes interspersed with comment nodes that are used for demarcation. This gives us the same ability to update individual pieces of text, without creating extra nested nodes. Very few people have depended on the actual markup generated here so it’s likely you are not impacted. However if you were targeting these <span>s in your CSS, you will need to adjust accordingly. You can always render them explicitly in your components. @mwiencek in #5753
  • Rendering null now uses comment nodes #

    We’ve also made use of these comment nodes to change what null renders to. Rendering to null was a feature we added in React 0.11 and was implemented by rendering <noscript> elements. By rendering to comment nodes now, there’s a chance some of your CSS will be targeting the wrong thing, specifically if you are making use of :nth-child selectors. React’s use of the <noscript> tag has always been considered an implementation detail of how React targets the DOM. We believe they are safe changes to make without going through a release with warnings detailing the subtle differences as they are details that should not be depended upon. Additionally, we have seen that these changes have improved React performance for many typical applications. @spicyj in #5451
  • Functional components can now return null too #

    We added support for defining stateless components as functions in React 0.14. However, React 0.14 still allowed you to define a class component without extending React.Component or using React.createClass(), so we couldn’t reliably tell if your component is a function or a class, and did not allow returning null from it. This issue is solved in React 15, and you can now return null from any component, whether it is a class or a function. @jimfb in #5884
  • Improved SVG support #

    All SVG tags are now fully supported. (Uncommon SVG tags are not present on the React.DOM element helper, but JSX and React.createElement work on all tag names.) All SVG attributes that are implemented by the browsers should be supported too. If you find any attributes that we have missed, please let us know in this issue. @zpao in #6243

Breaking changes #

  • No more extra <span>s #

    It’s worth calling out the DOM structure changes above again, in particular the change from <span>s. In the course of updating the Facebook codebase, we found a very small amount of code that was depending on the markup that React generated. Some of these cases were integration tests like WebDriver which were doing very specific XPath queries to target nodes. Others were simply tests using ReactDOM.renderToStaticMarkup and comparing markup. Again, there were a very small number of changes that had to be made, but we don’t want anybody to be blindsided. We encourage everybody to run their test suites when upgrading and consider alternative approaches when possible. One approach that will work for some cases is to explicitly use <span>s in your render method. @mwiencek in #5753
  • React.cloneElement() now resolves defaultProps #

    We fixed a bug in React.cloneElement() that some components may rely on. If some of the props received by cloneElement() are undefined, it used to return an element with undefined values for those props. In React 15, we’re changing it to be consistent with createElement(). Now any undefined props passed to cloneElement() are resolved to the corresponding component’s defaultProps. Only one of our 20,000 React components was negatively affected by this so we feel comfortable releasing this change without keeping the old behavior for another release cycle. @truongduy134 in #5997
  • ReactPerf.getLastMeasurements() is opaque #

    This change won’t affect applications but may break some third-party tools. We are revamping ReactPerf implementation and plan to release it during the 15.x cycle. The internal performance measurement format is subject to change so, for the time being, we consider the return value of ReactPerf.getLastMeasurements() an opaque data structure that should not be relied upon. @gaearon in #6286
  • Removed deprecations #

    These deprecations were introduced nine months ago in v0.14 with a warning and are removed:
    • Deprecated APIs are removed from the React top-level export: findDOMNode, render, renderToString, renderToStaticMarkup, and unmountComponentAtNode. As a reminder, they are now available on ReactDOM and ReactDOMServer. @jimfb in #5832
    • Deprecated addons are removed: batchedUpdates and cloneWithProps. @jimfb in #5859, @zpao in #6016
    • Deprecated component instance methods are removed: setProps, replaceProps, and getDOMNode. @jimfb in #5570
    • Deprecated CommonJS react/addons entry point is removed. As a reminder, you should use separate react-addons-* packages instead. This only applies if you use the CommonJS builds. @gaearon in #6285
    • Passing children to void elements like <input> was deprecated, and now throws an error. @jonhester in #3372
    • React-specific properties on DOM refs (e.g. this.refs.div.props) were deprecated, and are removed now. @jimfb in #5495

New deprecations, introduced with a warning #

Each of these changes will continue to work as before with a new warning until the release of React 16 so you can upgrade your code gradually.
  • LinkedStateMixin and valueLink are now deprecated due to very low popularity. If you need this, you can use a wrapper component that implements the same behavior: react-linked-input. @jimfb in #6127
  • Future versions of React will treat <input value={null}> as a request to clear the input. However, React 0.14 has been ignoring value={null}. React 15 warns you on a null input value and offers you to clarify your intention. To fix the warning, you may explicitly pass an empty string to clear a controlled input, or pass undefined to make the input uncontrolled. @antoaravinth in #5048
  • ReactPerf.printDOM() was renamed to ReactPerf.printOperations(), and ReactPerf.getMeasurementsSummaryMap() was renamed to ReactPerf.getWasted(). @gaearon in #6287

New helpful warnings #

  • If you use a minified copy of the development build, React DOM kindly encourages you to use the faster production build instead. @spicyj in #5083
  • React DOM: When specifying a unit-less CSS value as a string, a future version will not add px automatically. This version now warns in this case (ex: writing style={{width: '300'}}. Unitless number values like width: 300 are unchanged. @pluma in #5140
  • Synthetic Events will now warn when setting and accessing properties (which will not get cleared appropriately), as well as warn on access after an event has been returned to the pool. @kentcdodds in #5940 and @koba04 in #5947
  • Elements will now warn when attempting to read ref and key from the props. @prometheansacrifice in #5744
  • React will now warn if you pass a different props object to super() in the constructor. @prometheansacrifice in #5346
  • React will now warn if you call setState() inside getChildContext(). @raineroviir in #6121
  • React DOM now attempts to warn for mistyped event handlers on DOM elements, such as onclick which should be onClick. @ali in #5361
  • React DOM now warns about NaN values in style. @jontewks in #5811
  • React DOM now warns if you specify both value and defaultValue for an input. @mgmcdermott in #5823
  • React DOM now warns if an input switches between being controlled and uncontrolled. @TheBlasfem in #5864
  • React DOM now warns if you specify onFocusIn or onFocusOut handlers as they are unnecessary in React. @jontewks in #6296
  • React now prints a descriptive error message when you pass an invalid callback as the last argument to ReactDOM.render(), this.setState(), or this.forceUpdate(). @conorhastings in #5193 and @gaearon in #6310
  • Add-Ons: TestUtils.Simulate() now prints a helpful message if you attempt to use it with shallow rendering. @conorhastings in #5358
  • PropTypes: arrayOf() and objectOf() provide better error messages for invalid arguments. @chicoxyzzy in #5390

Notable bug fixes #

  • Fixed multiple small memory leaks. @spicyj in #4983 and @victor-homyakov in #6309
  • Input events are handled more reliably in IE 10 and IE 11; spurious events no longer fire when using a placeholder. @jquense in #4051
  • The componentWillReceiveProps() lifecycle method is now consistently called when context changes. @milesj in #5787
  • React.cloneElement() doesn’t append slash to an existing key when used inside React.Children.map(). @ianobermiller in #5892
  • React DOM now supports the cite and profile HTML attributes. @AprilArcus in #6094 and @saiichihashimoto in #6032
  • React DOM now supports cssFloat, gridRow and gridColumn CSS properties. @stevenvachon in #6133 and @mnordick in #4779
  • React DOM now correctly handles borderImageOutset, borderImageWidth, borderImageSlice, floodOpacity, strokeDasharray, and strokeMiterlimit as unitless CSS properties. @rofrischmann in #6210 and #6270
  • React DOM now supports the onAnimationStart, onAnimationEnd, onAnimationIteration, onTransitionEnd, and onInvalid events. Support for onLoad has been added to object elements. @tomduncalf in #5187, @milesj in #6005, and @ara4n in #5781
  • React DOM now defaults to using DOM attributes instead of properties, which fixes a few edge case bugs. Additionally the nullification of values (ex: href={null}) now results in the forceful removal, no longer trying to set to the default value used by browsers in the absence of a value. @syranide in #1510
  • React DOM does not mistakingly coerce children to strings for Web Components. @jimfb in #5093
  • React DOM now correctly normalizes SVG <use> events. @edmellum in #5720
  • React DOM does not throw if a <select> is unmounted while its onChange handler is executing. @sambev in #6028
  • React DOM does not throw in Windows 8 apps. @Andrew8xx8 in #6063
  • React DOM does not throw when asynchronously unmounting a child with a ref. @yiminghe in #6095
  • React DOM no longer forces synchronous layout because of scroll position tracking. @syranide in #2271
  • Object.is is used in a number of places to compare values, which leads to fewer false positives, especially involving NaN. In particular, this affects the shallowCompare add-on. @chicoxyzzy in #6132
  • Add-Ons: ReactPerf no longer instruments adding or removing an event listener because they don’t really touch the DOM due to event delegation. @antoaravinth in #5209

 Other improvements #

  • React now uses loose-envify instead of envify so it installs fewer transitive dependencies. @qerub in #6303
  • Shallow renderer now exposes getMountedInstance(). @glenjamin in #4918
  • Shallow renderer now returns the rendered output from render(). @simonewebdesign in #5411
  • React no longer depends on ES5 shams for Object.create and Object.freeze in older environments. It still, however, requires ES5 shims in those environments. @dgreensp in #4959
  • React DOM now allows data- attributes with names that start with numbers. @nLight in #5216
  • React DOM adds a new suppressContentEditableWarning prop for components like Draft.js that intentionally manage contentEditable children with React. @mxstbr in #6112
  • React improves the performance for createClass() on complex specs. @spicyj in #5550