React v0.13

By Sophie Alpert·

Today, we’re happy to release React v0.13!

The most notable new feature is support for ES6 classes, which allows developers to have more flexibility when writing components. Our eventual goal is for ES6 classes to replace React.createClass completely, but until we have a replacement for current mixin use cases and support for class property initializers in the language, we don’t plan to deprecate React.createClass.

At EmberConf and ng-conf last week, we were excited to see that Ember and Angular have been working on speed improvements and now both have performance comparable to React. We’ve always thought that performance isn’t the most important reason to choose React, but we’re still planning more optimizations to make React even faster.

Our planned optimizations require that ReactElement objects are immutable, which has always been a best practice when writing idiomatic React code. In this release, we’ve added runtime warnings that fire when props are changed or added between the time an element is created and when it’s rendered. When migrating your code, you may want to use new React.cloneElement API (which is similar to React.addons.cloneWithProps but preserves key and ref and does not merge style or className automatically). For more information about our planned optimizations, see GitHub issues #3226, #3227, #3228.

The release is now available for download:

We’ve also published version 0.13.0 of the react and react-tools packages on npm and the react package on bower.

Changelog

React Core

Breaking Changes

  • Deprecated patterns that warned in 0.12 no longer work: most prominently, calling component classes without using JSX or React.createElement and using non-component functions with JSX or createElement
  • Mutating props after an element is created is deprecated and will cause warnings in development mode; future versions of React will incorporate performance optimizations assuming that props aren’t mutated
  • Static methods (defined in statics) are no longer autobound to the component class
  • ref resolution order has changed slightly such that a ref to a component is available immediately after its componentDidMount method is called; this change should be observable only if your component calls a parent component’s callback within your componentDidMount, which is an anti-pattern and should be avoided regardless
  • Calls to setState in life-cycle methods are now always batched and therefore asynchronous. Previously the first call on the first mount was synchronous.
  • setState and forceUpdate on an unmounted component now warns instead of throwing. That avoids a possible race condition with Promises.
  • Access to most internal properties has been completely removed, including this._pendingState and this._rootNodeID.

New Features

  • Support for using ES6 classes to build React components; see the v0.13.0 beta 1 notes for details.
  • Added new top-level API React.findDOMNode(component), which should be used in place of component.getDOMNode(). The base class for ES6-based components will not have getDOMNode. This change will enable some more patterns moving forward.
  • Added a new top-level API React.cloneElement(el, props) for making copies of React elements – see the v0.13 RC2 notes for more details.
  • New ref style, allowing a callback to be used in place of a name: <Photo ref={(c) => this._photo = c} /> allows you to reference the component with this._photo (as opposed to ref="photo" which gives this.refs.photo).
  • this.setState() can now take a function as the first argument for transactional state updates, such as this.setState((state, props) => ({count: state.count + 1})); – this means that you no longer need to use this._pendingState, which is now gone.
  • Support for iterators and immutable-js sequences as children.

Deprecations

  • ComponentClass.type is deprecated. Just use ComponentClass (usually as element.type === ComponentClass).
  • Some methods that are available on createClass-based components are removed or deprecated from ES6 classes (getDOMNode, replaceState, isMounted, setProps, replaceProps).

React with Add-Ons

New Features

Deprecations

  • React.addons.classSet is now deprecated. This functionality can be replaced with several freely available modules. classnames is one such module.
  • Calls to React.addons.cloneWithProps can be migrated to use React.cloneElement instead – make sure to merge style and className manually if desired.

React Tools

Breaking Changes

  • When transforming ES6 syntax, class methods are no longer enumerable by default, which requires Object.defineProperty; if you support browsers such as IE8, you can pass --target es3 to mirror the old behavior

New Features

  • --target option is available on the jsx command, allowing users to specify and ECMAScript version to target.
    • es5 is the default.
    • es3 restores the previous default behavior. An additional transform is added here to ensure the use of reserved words as properties is safe (eg this.static will become this['static'] for IE8 compatibility).
  • The transform for the call spread syntax has also been enabled.

JSX

Breaking Changes

  • A change was made to how some JSX was parsed, specifically around the use of > or } when inside an element. Previously it would be treated as a string but now it will be treated as a parse error. The jsx_orphaned_brackets_transformer package on npm can be used to find and fix potential issues in your JSX code.