* 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](http://facebook.github.io/react/blog/2015/01/27/react-v0.13.0-beta-1.html) 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](/react/blog/2015/03/03/react-v0.13-rc2.html#react.cloneelement) 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
* [`React.addons.createFragment` was added](/react/docs/create-fragment.html) for adding keys to entire sets of children.
#### Deprecations
*`React.addons.classSet` is now deprecated. This functionality can be replaced with several freely available modules. [classnames](https://www.npmjs.com/package/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 operator 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`](https://www.npmjs.com/package/jsx_orphaned_brackets_transformer) package on npm can be used to find and fix potential issues in your JSX code.
*`key` and `ref` moved off props object, now accessible on the element directly
* React is now BSD licensed with accompanying Patents grant
* Default prop resolution has moved to Element creation time instead of mount time, making them effectively static
*`React.__internals` is removed - it was exposed for DevTools which no longer needs access
* Composite Component functions can no longer be called directly - they must be wrapped with `React.createFactory` first. This is handled for you when using JSX.
#### New Features
* Spread operator (`{...}`) introduced to deprecate `this.transferPropsTo`
* Added support for more HTML attributes: `acceptCharset`, `classID`, `manifest`
* **DEPRECATED** Returning `false` from event handlers to preventDefault
* **DEPRECATED** Convenience Constructor usage as function, instead wrap with `React.createFactory`
* **DEPRECATED** use of `key={null}` to assign implicit keys
#### Bug Fixes
* Better handling of events and updates in nested results, fixing value restoration in "layered" controlled components
* Correctly treat `event.getModifierState` as case sensitive
* Improved normalization of `event.charCode`
* Better error stacks when involving autobound methods
* Removed DevTools message when the DevTools are installed
* Correctly detect required language features across browsers
* Fixed support for some HTML attributes:
*`list` updates correctly now
*`scrollLeft`, `scrollTop` removed, these should not be specified as props
* Improved error messages
### React With Addons
#### New Features
*`React.addons.batchedUpdates` added to API for hooking into update cycle
#### Breaking Changes
*`React.addons.update` uses `assign` instead of `copyProperties` which does `hasOwnProperty` checks. Properties on prototypes will no longer be updated correctly.
#### Bug Fixes
* Fixed some issues with CSS Transitions
### JSX
#### Breaking Changes
* Enforced convention: lower case tag names are always treated as HTML tags, upper case tag names are always treated as composite components
* JSX no longer transforms to simple function calls
#### New Features
*`@jsx React.DOM` no longer required
* spread (`{...}`) operator introduced to allow easier use of props
#### Bug Fixes
* JSXTransformer: Make sourcemaps an option when using APIs directly (eg, for react-rails)
* Keyboard events include normalized `e.key` and `e.getModifierState()` properties
* New normalized `onBeforeInput` event
*`React.Children.count` has been added as a helper for counting the number of children
#### Bug Fixes
* Re-renders are batched in more cases
* Events: `e.view` properly normalized
* Added Support for more HTML attributes (`coords`, `crossOrigin`, `download`, `hrefLang`, `mediaGroup`, `muted`, `scrolling`, `shape`, `srcSet`, `start`, `useMap`)
* Improved SVG support
* Changing `className` on a mounted SVG component now works correctly
* Added support for elements `mask` and `tspan`
* Added support for attributes `dx`, `dy`, `fillOpacity`, `fontFamily`, `fontSize`, `markerEnd`, `markerMid`, `markerStart`, `opacity`, `patternContentUnits`, `patternUnits`, `preserveAspectRatio`, `strokeDasharray`, `strokeOpacity`
* CSS property names with vendor prefixes (`Webkit`, `ms`, `Moz`, `O`) are now handled properly
* Duplicate keys no longer cause a hard error; now a warning is logged (and only one of the children with the same key is shown)
*`img` event listeners are now unbound properly, preventing the error "Two valid but unequal nodes with the same `data-reactid`"
* Added explicit warning when missing polyfills
### React With Addons
* PureRenderMixin: a mixin which helps optimize "pure" components
* Perf: a new set of tools to help with performance analysis
* Update: New `$apply` command to transform values
* TransitionGroup bug fixes with null elements, Android
### React NPM Module
* Now includes the pre-built packages under `dist/`.
*`envify` is properly listed as a dependency instead of a peer dependency
### JSX
* Added support for namespaces, eg `<Components.Checkbox />`
* JSXTransformer
* Enable the same `harmony` features available in the command line with `<script type="text/jsx;harmony=true">`
* Scripts are downloaded in parallel for more speed. They are still executed in order (as you would expect with normal script tags)
* Fixed a bug preventing sourcemaps from working in Firefox
### React Tools Module
* Improved readme with usage and API information
* Improved ES6 transforms available with `--harmony` option
* Added `--source-map-inline` option to the `jsx` executable
* New `transformWithDetails` API which gives access to the raw sourcemap data
* Added warnings to help migrate towards descriptors
* Made it possible to server render without React-related markup (`data-reactid`, `data-react-checksum`). This DOM will not be mountable by React. [Read the docs for `React.renderComponentToStaticMarkup`](http://facebook.github.io/react/docs/top-level-api.html#react.rendercomponenttostaticmarkup)
* Added support for more attributes:
*`srcSet` for `<img>` to specify images at different pixel ratios
*`textAnchor` for SVG
#### Bug Fixes
* Ensure all void elements don’t insert a closing tag into the markup.
* Ensure `className={false}` behaves consistently
* Ensure `this.refs` is defined, even if no refs are specified.
### Addons
*`update` function to deal with immutable data. [Read the docs](http://facebook.github.io/react/docs/update.html)
### react-tools
* Added an option argument to `transform` function. The only option supported is `harmony`, which behaves the same as `jsx --harmony` on the command line. This uses the ES6 transforms from [jstransform](https://github.com/facebook/jstransform).
- The lifecycle methods `componentDidMount` and `componentDidUpdate` no longer receive the root node as a parameter; use `this.getDOMNode()` instead
- Whenever a prop is equal to `undefined`, the default value returned by `getDefaultProps` will now be used instead
-`React.unmountAndReleaseReactRootNode` was previously deprecated and has now been removed
-`React.renderComponentToString` is now synchronous and returns the generated HTML string
- Full-page rendering (that is, rendering the `<html>` tag using React) is now supported only when starting with server-rendered markup
- On mouse wheel events, `deltaY` is no longer negated
- When prop types validation fails, a warning is logged instead of an error thrown (with the production build of React, type checks are now skipped for performance)
- On `input`, `select`, and `textarea` elements, `.getValue()` is no longer supported; use `.getDOMNode().value` instead
- React now never rethrows errors, so stack traces are more accurate and Chrome's purple break-on-error stop sign now works properly
- Added support for SVG tags `defs`, `linearGradient`, `polygon`, `radialGradient`, `stop`
- Added support for more attributes:
-`crossOrigin` for CORS requests
-`download` and `hrefLang` for `<a>` tags
-`mediaGroup` and `muted` for `<audio>` and `<video>` tags
-`noValidate` and `formNoValidate` for forms
-`property` for Open Graph `<meta>` tags
-`sandbox`, `seamless`, and `srcDoc` for `<iframe>` tags
-`scope` for screen readers
-`span` for `<colgroup>` tags
- Added support for defining `propTypes` in mixins
- Added `any`, `arrayOf`, `component`, `oneOfType`, `renderable`, `shape` to `React.PropTypes`
- Added support for `statics` on component spec for static component methods
- On all events, `.currentTarget` is now properly set
- On keyboard events, `.key` is now polyfilled in all browsers for special (non-printable) keys
- On clipboard events, `.clipboardData` is now polyfilled in IE
- On drag events, `.dragTransfer` is now present
- Added support for `onMouseOver` and `onMouseOut` in addition to the existing `onMouseEnter` and `onMouseLeave` events
- Added support for `onLoad` and `onError` on `<img>` elements
- Added support for `onReset` on `<form>` elements
- The `autoFocus` attribute is now polyfilled consistently on `input`, `select`, and `textarea`
#### Bug Fixes
- React no longer adds an `__owner__` property to each component's `props` object; passed-in props are now never mutated
- When nesting top-level components (e.g., calling `React.renderComponent` within `componentDidMount`), events now properly bubble to the parent component
- Fixed a case where nesting top-level components would throw an error when updating
- Passing an invalid or misspelled propTypes type now throws an error
- On mouse enter/leave events, `.target`, `.relatedTarget`, and `.type` are now set properly
- On composition events, `.data` is now properly normalized in IE9 and IE10
- CSS property values no longer have `px` appended for the unitless properties `columnCount`, `flex`, `flexGrow`, `flexShrink`, `lineClamp`, `order`, `widows`
- Fixed a memory leak when unmounting children with a `componentWillUnmount` handler
- Fixed a memory leak when `renderComponentToString` would store event handlers
- Fixed an error that could be thrown when removing form elements during a click handler
- Boolean attributes such as `disabled` are rendered without a value (previously `disabled="true"`, now simply `disabled`)
-`key` values containing `.` are now supported
- Shortened `data-reactid` values for performance
- Components now always remount when the `key` property changes
- Event handlers are attached to `document` only when necessary, improving performance in some cases
- Events no longer use `.returnValue` in modern browsers, eliminating a warning in Chrome
-`scrollLeft` and `scrollTop` are no longer accessed on document.body, eliminating a warning in Chrome
- General performance fixes, memory optimizations, improvements to warnings and error messages
### React with Addons
-`React.addons.TestUtils` was added to help write unit tests
-`React.addons.TransitionGroup` was renamed to `React.addons.CSSTransitionGroup`
-`React.addons.TransitionGroup` was added as a more general animation wrapper
-`React.addons.cloneWithProps` was added for cloning components and modifying their props
- Bug fix for adding back nodes during an exit transition for CSSTransitionGroup
- Bug fix for changing `transitionLeave` in CSSTransitionGroup
- Performance optimizations for CSSTransitionGroup
- On checkbox `<input>` elements, `checkedLink` is now supported for two-way binding
### JSX Compiler and react-tools Package
- Whitespace normalization has changed; now space between two tags on the same line will be preserved, while newlines between two tags will be removed
- The `react-tools` npm package no longer includes the React core libraries; use the `react` package instead.
-`displayName` is now added in more cases, improving error messages and names in the React Dev Tools
- Fixed an issue where an invalid token error was thrown after a JSX closing tag
-`JSXTransformer` now uses source maps automatically in modern browsers
-`JSXTransformer` error messages now include the filename and problematic line contents when a file fails to parse
* Memory usage improvements - reduced allocations in core which will help with GC pauses
* Performance improvements - in addition to speeding things up, we made some tweaks to stay out of slow path code in V8 and Nitro.
* Standardized prop -> DOM attribute process. This previously resulting in additional type checking and overhead as well as confusing cases for users. Now we will always convert your value to a string before inserting it into the DOM.
* Support for Selection events.
* Support for [Composition events](https://developer.mozilla.org/en-US/docs/Web/API/CompositionEvent).
* Support for additional DOM properties (`charSet`, `content`, `form`, `httpEquiv`, `rowSpan`, `autoCapitalize`).
* Support for additional SVG properties (`rx`, `ry`).
* Support for using `getInitialState` and `getDefaultProps` in mixins.
* Support mounting into iframes.
* Bug fixes for controlled form components.
* Bug fixes for SVG element creation.
* Added `React.version`.
* Added `React.isValidClass` - Used to determine if a value is a valid component constructor.
* Removed `React.autoBind` - This was deprecated in v0.4 and now properly removed.
* Renamed `React.unmountAndReleaseReactRootNode` to `React.unmountComponentAtNode`.
* Began laying down work for refined performance analysis.
* Better support for server-side rendering - [react-page](https://github.com/facebook/react-page) has helped improve the stability for server-side rendering.
* Made it possible to use React in environments enforcing a strict [Content Security Policy](https://developer.mozilla.org/en-US/docs/Security/CSP/Introducing_Content_Security_Policy). This also makes it possible to use React to build Chrome extensions.
### React with Addons (New!)
* Introduced a separate build with several "addons" which we think can help improve the React experience. We plan to deprecate this in the long-term, instead shipping each as standalone pieces. [Read more in the docs](http://facebook.github.io/react/docs/addons.html).
### JSX
* No longer transform `class` to `className` as part of the transform! This is a breaking change - if you were using `class`, you *must* change this to `className` or your components will be visually broken.
* Added warnings to the in-browser transformer to make it clear it is not intended for production use.
* Improved compatibility for Windows
* Improved support for maintaining line numbers when transforming.
* Switch from using `id` attribute to `data-reactid` to track DOM nodes. This allows you to integrate with other JS and CSS libraries more easily.
* Support for more DOM elements and attributes (e.g., `<canvas>`)
* Improved server-side rendering APIs. `React.renderComponentToString(<component>, callback)` allows you to use React on the server and generate markup which can be sent down to the browser.
*`prop` improvements: validation and default values. [Read our blog post for details...](http://facebook.github.io/react/blog/2013/07/11/react-v0-4-prop-validation-and-default-values.html)
* Support for the `key` prop, which allows for finer control over reconciliation. [Read the docs for details...](http://facebook.github.io/react/docs/multiple-components.html)
* Removed `React.autoBind`. [Read our blog post for details...](http://facebook.github.io/react/blog/2013/07/02/react-v0-4-autobind-by-default.html)
* Improvements to forms. We've written wrappers around `<input>`, `<textarea>`, `<option>`, and `<select>` in order to standardize many inconsistencies in browser implementations. This includes support for `defaultValue`, and improved implementation of the `onChange` event, and circuit completion. [Read the docs for details...](http://facebook.github.io/react/docs/forms.html)
* We've implemented an improved synthetic event system that conforms to the W3C spec.
* Updates to your component are batched now, which may result in a significantly faster re-render of components. `this.setState` now takes an optional callback as it's second parameter. If you were using `onClick={this.setState.bind(this, state)}` previously, you'll want to make sure you add a third parameter so that the event is not treated as the callback.
### JSX
* Support for comment nodes `<div>{/* this is a comment and won't be rendered */}</div>`
* Children are now transformed directly into arguments instead of being wrapped in an array
* Allow reusing the same DOM node to render different components. e.g. `React.renderComponent(<div/>, domNode); React.renderComponent(<span/>, domNode);` will work now.
### JSX
* Improved the in-browser transformer so that transformed scripts will execute in the expected scope. The allows components to be defined and used from separate files.
* Upgrade Commoner so `require` statements are no longer relativized when passing through the transformer. This was a feature needed when building React, but doesn't translate well for other consumers of `bin/jsx`.
* Upgraded our dependencies on Commoner and Recast so they use a different directory for their cache.
* Switch from using the browserified build to shipping individual modules. This allows react-tools to be used with [browserify](https://github.com/substack/node-browserify).
