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React v0.10 RC

19 mars 2014 par Paul O’Shannessy

This blog site has been archived. Go to react.dev/blog to see the recent posts.

v0.9 has only been out for a month, but we’re getting ready to push out v0.10 already. Unlike v0.9 which took a long time, we don’t have a long list of changes to talk about.

The release candidate is available for download from the CDN:

We’ve also published version 0.10.0-rc1 of the react and react-tools packages on npm and the react package on bower.

Please try these builds out and file an issue on GitHub if you see anything awry.

Clone On Mount

The main purpose of this release is to provide a smooth upgrade path as we evolve some of the implementation of core. In v0.9 we started warning in cases where you called methods on unmounted components. This is part of an effort to enforce the idea that the return value of a component (React.DOM.div(), MyComponent()) is in fact not a reference to the component instance React uses in the virtual DOM. The return value is instead a light-weight object that React knows how to use. Since the return value currently is a reference to the same object React uses internally, we need to make this transition in stages as many people have come to depend on this implementation detail.

In 0.10, we’re adding more warnings to catch a similar set of patterns. When a component is mounted we clone it and use that object for our internal representation. This allows us to capture calls you think you’re making to a mounted component. We’ll forward them on to the right object, but also warn you that this is breaking. See “Access to the Mounted Instance” on this page. Most of the time you can solve your pattern by using refs.

Storing a reference to your top level component is a pattern touched upon on that page, but another examples that demonstrates what we see a lot of:

// This is a common pattern. However instance here really refers to a
// "descriptor", not necessarily the mounted instance.
var instance = <MyComponent/>;
// ...

// The change here is very simple. The return value of renderComponent will be
// the mounted instance.
var instance = React.renderComponent(<MyComponent/>)
// ...

These warnings and method forwarding are only enabled in the development build. The production builds continue to work as they did in v0.9. We strongly encourage you to use the development builds to catch these warnings and fix the call sites.

The plan for v0.11 is that we will go fully to “descriptors”. Method calls on the return value of MyComponent() will fail hard.


React Core

New Features

  • 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
  • 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.



  • 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.
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