I'm excited to announce that today we're releasing React v0.9, which incorporates many bug fixes and several new features since the last release. This release contains almost four months of work, including over 800 commits from over 70 committers!
Thanks to everyone who tested the release candidate; we were able to find and fix an error in the event handling code, we upgraded envify to make running browserify on React faster, and we added support for five new attributes.
As always, the release is available for download from the CDN:
This version includes better support for normalizing event properties across all supported browsers so that you need to worry even less about cross-browser differences. We've also made many improvements to error messages and have refactored the core to never rethrow errors, so stack traces are more accurate and Chrome's purple break-on-error stop sign now works properly.
We've also added to the add-ons build [React.addons.TestUtils](/docs/test-utils.html), a set of new utilities to help you write unit tests for React components. You can now simulate events on your components, and several helpers are provided to help make assertions about the rendered DOM tree.
In addition to the changes to React core listed below, we've made a small change to the way JSX interprets whitespace to make things more consistent. With this release, space between two components on the same line will be preserved, while a newline separating a text node from a tag will be eliminated in the output. Consider the code:
```html
<div>
Monkeys:
{listOfMonkeys} {submitButton}
</div>
```
In v0.8 and below, it was transformed to the following:
```javascript
React.DOM.div(null,
" Monkeys: ",
listOfMonkeys, submitButton
)
```
In v0.9, it will be transformed to this JS instead:
In cases where you want to preserve the space adjacent to a newline, you can write `{'Monkeys: '}` or `Monkeys:{' '}` in your JSX source. We've included a script to do an automated codemod of your JSX source tree that preserves the old whitespace behavior by adding and removing spaces appropriately. You can [install jsx\_whitespace\_transformer from npm](https://github.com/facebook/react/blob/main/npm-jsx_whitespace_transformer/README.md) and run it over your source tree to modify files in place. The transformed JSX files will preserve your code's existing whitespace behavior.
- 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 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
