React v0.13 RC

February 24, 2015 by Paul O’Shannessy

Over the weekend we pushed out our first (and hopefully only) release candidate for React v0.13!

We’ve talked a little bit about the changes that are coming. The splashiest of these changes is support for ES6 Classes. You can read more about this in our beta announcement. We’re really excited about this! Sebastian also posted earlier this morning about some of the other changes coming focused around ReactElement. The changes we’ve been working on there will hopefully enable lots of improvements to performance and developer experience.

The release candidate is available for download:

We’ve also published version 0.13.0-rc1 of the react and react-tools packages on npm and the react package on bower.


React Core

Breaking Changes

  • 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.
  • 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.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


  • 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 (for example, getDOMNode, setProps, replaceState).

React with Add-Ons


  • React.addons.classSet is now deprecated. This functionality can be replaced with several freely available modules. classnames is one such module.

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 restored 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 operator has also been enabled.


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. We will be releasing a standalone executable to find and fix potential issues in your JSX code.