- 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).