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Update changelog for unreleased 16.0 changes #10730

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44 changes: 44 additions & 0 deletions CHANGELOG.md
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## [Unreleased]
<details>
<summary>
Changes that have landed in master but are not yet released.
Click to see more.
</summary>

### JS Environment Requirements
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What about requestAnimationFrame?

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good_catch_corgi

will fix!

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Maybe worth changing to "New JS Environment Requirements" to better signal it is a change.


* **React 16 depends on the collection types [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) and [Set](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set), as well as [requestAnimationFrame](https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame).** If you support older browsers and devices which may not yet provide these natively (eg <IE11), consider including a global polyfill in your bundled application, such as [core-js](https://github.com/zloirock/core-js) or [babel-polyfill](https://babeljs.io/docs/usage/polyfill/).
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I would prefer we don't advertise core-js and babel-polyfill in this way without a specific example. I believe we had an example somewhere (in the issue?)

The trouble with this wording is it looks like we're promoting importing the whole polyfill (e.g. import 'babel-polyfill'). We should not. They are huge!

In the example we had, we specifically imported only the necessary ones.

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(We don't have to literally paste an example here. It's enough to link to the docs, where we might want to add the same info anyway. Or we could link to a gist.)

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Sounds good! Will fix.


### Major Changes

* **Improved error handling with introduction of "error boundaries".** [Error boundaries](https://facebook.github.io/react/blog/2017/07/26/error-handling-in-react-16.html) are React components that catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI instead of the component tree that crashed.
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I would prefer if we separated error boundaries and portals into a separate "New Features" section. We could also add that components can now return arrays and strings into it, and that custom DOM attributes are now passed through (since it's technically one of top requested features).

Then the second section would be "Breaking Changes". It's fine to repeat the "unknown attributes" thing there since in addition to being a new feature, it's also a breaking change. But other new features (portals, arrays, error boundaries) are not.

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Sweet! I was struggling to find the groupings within 'major changes' and I really like those two. Will fix.

- **There are several changes to the behavior of scheduling and lifecycle methods:**
* `ReactDOM.render()` and `ReactDOM.unstable_renderIntoContainer()` now return `null` if called from inside a lifecycle method.
* To work around this, you can either use [the new portal API](https://github.com/facebook/react/issues/10309#issuecomment-318433235) or [refs](https://github.com/facebook/react/issues/10309#issuecomment-318434635).
* `setState`:
* Calling `setState` with null no longer triggers an update. This allows you to decide in an updater function if you want to re-render.
* Calling `setState` directly in render always causes an update. This was not previously the case. Regardless, you should not be calling setState from render.
* `setState` callback (second argument) now fires immediately after `componentDidMount` / `componentDidUpdate` instead of after all components have rendered.
* When replacing `<A />` with `<B />`, `B.componentWillMount` now always happens before `A.componentWillUnmount`. Previously, `A.componentWillUnmount` could fire first in some cases.
* Previously, changing the ref to a component would always detach the ref before that component's render is called. Now, we change the ref later, when applying the changes to the DOM.
* It is not safe to re-render into a container that was modified by something other than React. This worked previously in some cases but was never supported. We now emit a warning in this case. Instead you should clean up your component trees using `ReactDOM.unmountComponentAtNode`. [See this example.](https://github.com/facebook/react/issues/10294#issuecomment-318820987)
* `componentDidUpdate` lifecycle no longer receives `prevContext` param. (See #8631)
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This will not turn into a link in a Markdown file. GH only linkifies in comments and issues.

* Shallow renderer no longer calls `componentDidUpdate()` because DOM refs are not available. This also makes it consistent with `componentDidMount()` (which does not get called in previous versions either).
* Shallow renderer does not implement `unstable_batchedUpdates()` anymore.
- **The names and paths to the single-file browser builds have changed to emphasize the difference between development and production builds.** For example:
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Nit: not clear why this one is bold but others aren't

- react/dist/react.js → react/umd/react.development.js
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We should put filenames in backticks for nicer formatting.

- react/dist/react.min.js → react/umd/react.production.min.js
- react-dom/dist/react-dom.js → react-dom/umd/react-dom.development.js
- react-dom/dist/react-dom.min.js → react-dom/umd/react-dom.production.min.js
* ReactDOM.createPortal() is official and stable
([@gaearon](https://github.com/gaearon) in
[10675](https://github.com/facebook/react/pull/10675))
* Allow [passing some "unknown" attributes through to DOM components](https://facebook.github.io/react/blog/2017/09/08/dom-attributes-in-react-16.html) (@nhunzaker in https://github.com/facebook/react/pull/10385 , https://github.com/facebook/react/pull/10564 , https://github.com/facebook/react/pull/10495 and others)
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This also looks pretty bad in Markdown file. These need to be turned into real links.


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I think we should add a separate point about error boundaries here as it is a breaking change. Specifically:

  • Errors in the render and lifecycle methods now unmount the component tree by default. To prevent this, add error boundaries to the appropriate places in the UI. (And make it a link)

### Removed deprecations
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Capitalisation nit to match other sections: Removed Deprecations


- **There is no react-with-addons.js build anymore.** All compatible addons are published separately on npm, and have single-file browser versions if you need them.
- **The deprecations introduced in 15.x have been removed from the core package.** React.createClass is now available as create-react-class, React.PropTypes as prop-types, React.DOM as react-dom-factories, react-addons-test-utils as react-dom/test-utils, and shallow renderer as react-test-renderer/shallow. See [15.5.0](https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html) and [15.6.0](https://facebook.github.io/react/blog/2017/06/13/react-v15.6.0.html) blog posts for instructions on migrating code and automated codemods.

</details>

## 15.6.1 (June 14, 2017)

### React DOM
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