react.dev/content/blog/2018-05-23-react-v-16-4.md

---
title: "React v16.4.0: Experimental Component Profiler and Bugfixes"
author: [acdlite, bvaughn]
---

React 16.4 is a minor release that includes an experimental component profiler, as well as a crucial bugfix for `getDerivedStateFromProps`.

## `React.unstable_Profiler`

TODO (@bvaughn)

## Bugfix for `getDerivedStateFromProps`

`getDerivedStateFromProps` is now called every time a component is rendered, regardless of the cause of the update. Previously, it was only called if the component was re-rendered by its parent; it would not fire as the result of a local `setState`. This was an oversight in the initial implementation that has now been corrected. The previous behavior was more similar to how `componentWillReceiveProps` works, but the improved behavior ensures compatibility with React's upcoming asynchronous rendering mode.

**Most likely, this doesn't require any changes to your components**. The rare cases where it does matter fall into one of two categories:

### Avoid Side Effects in `getDerivedStateFromProps`

Like the render method, `getDerivedStateFromProps` should be a pure function of props and state. You should move side-effectful code elsewhere. E.g. Flux dispatches typically belong inside the originating event handler; DOM mutations belong inside `componentDidMount` or `componentDidUpdate`.

Side effects in `getDerivedStateFromProps` were already disallowed, but since it now fires more often than it used to, the recent change may expose previously undiscovered bugs.

### Compare Incoming Props to Previous Props When Computing Controlled Values

The following code assumes `getDerivedStateFromProps` only fires on prop changes. But since it now fires for state changes, too, local updates to the controlled value will be ignored, since the props version always overrides it.

```js
static getDerivedStateFromProps(props, state) {
  if (props.value !== state.controlledValue) {
    return {
      // Props always win. Oops!
      controlledValue: props.value,
    };
  }
  return null;
}
```

You can change it to do this instead:

```js
static getDerivedStateFromProps(props, state) {
  const prevProps = state.prevProps;
  // Compare incoming props to previous props
  const controlledValue =
    prevProps.value !== props.value
      ? props.value
      : state.controlledValue;
  return {
    // Store the previous props in state
    prevProps: props,
    controlledValue,
  };
}
```

## Installation

React v16.4.0 is available on the npm registry.

To install React 16 with Yarn, run:

```bash
yarn add react@^16.4.0 react-dom@^16.4.0
```

To install React 16 with npm, run:

```bash
npm install --save react@^16.4.0 react-dom@^16.4.0
```

We also provide UMD builds of React via a CDN:

```html
<script crossorigin src="https://unpkg.com/react@16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script>
```

Refer to the documentation for [detailed installation instructions](/docs/installation.html).

## Changelog

### React

* Add a new [experimental](https://github.com/reactjs/rfcs/pull/51) `React.unstable_Profiler` component for measuring performance. ([@bvaughn](https://github.com/bvaughn) in [#12745](https://github.com/facebook/react/pull/12745))

### React DOM

* Add support for the Pointer Events specification. ([@philipp-spiess](https://github.com/philipp-spiess) in [#12507](https://github.com/facebook/react/pull/12507))
* Properly call `getDerivedStateFromProps()` regardless of the reason for re-rendering. ([@acdlite](https://github.com/acdlite) in [#12600](https://github.com/facebook/react/pull/12600) and [#12802](https://github.com/facebook/react/pull/12802))
* Fix a bug that prevented context propagation in some cases. ([@gaearon](https://github.com/gaearon) in [#12708](https://github.com/facebook/react/pull/12708))
* Fix re-rendering of components using `forwardRef()` on a deeper `setState()`. ([@gaearon](https://github.com/gaearon) in [#12690](https://github.com/facebook/react/pull/12690))
* Fix some attributes incorrectly getting removed from custom element nodes. ([@airamrguez](https://github.com/airamrguez) in [#12702](https://github.com/facebook/react/pull/12702))
* Fix context providers to not bail out on children if there's a legacy context provider above. ([@gaearon](https://github.com/gaearon) in [#12586](https://github.com/facebook/react/pull/12586))
* Add the ability to specify `propTypes` on a context provider component. ([@nicolevy](https://github.com/nicolevy) in [#12658](https://github.com/facebook/react/pull/12658))
* Fix a false positive warning when using `react-lifecycles-compat` in `<StrictMode>`. ([@bvaughn](https://github.com/bvaughn) in [#12644](https://github.com/facebook/react/pull/12644))
* Warn when the `forwardRef()` render function has `propTypes` or `defaultProps`. ([@bvaughn](https://github.com/bvaughn) in [#12644](https://github.com/facebook/react/pull/12644))
* Improve how `forwardRef()` and context consumers are displayed in the component stack. ([@sophiebits](https://github.com/sophiebits) in [#12777](https://github.com/facebook/react/pull/12777))
* Change internal event names. This can break third-party packages that rely on React internals in unsupported ways. ([@philipp-spiess](https://github.com/philipp-spiess) in [#12629](https://github.com/facebook/react/pull/12629))

### React Test Renderer

* Fix the `getDerivedStateFromProps()` support to match the new React DOM behavior. ([@koba04](https://github.com/koba04) in [#12676](https://github.com/facebook/react/pull/12676))
* Fix a `testInstance.parent` crash when the parent is a fragment or another special node. ([@gaearon](https://github.com/gaearon) in [#12813](https://github.com/facebook/react/pull/12813))
* `forwardRef()` components are now discoverable by the test renderer traversal methods. ([@gaearon](https://github.com/gaearon) in [#12725](https://github.com/facebook/react/pull/12725))
* Shallow renderer now ignores `setState()` updaters that return `null` or `undefined`. ([@koba04](https://github.com/koba04) in [#12756](https://github.com/facebook/react/pull/12756))

### React ART

* Fix reading context provided from the tree managed by React DOM. ([@acdlite](https://github.com/acdlite) in [#12779](https://github.com/facebook/react/pull/12779))

### React Call Return (Experimental)

* This experiment was deleted because it was affecting the bundle size and the API wasn't good enough. It's likely to come back in the future in some other form. ([@gaearon](https://github.com/gaearon) in [#12820](https://github.com/facebook/react/pull/12820))

### React Reconciler (Experimental)

* The [new host config shape](https://github.com/facebook/react/blob/c601f7a64640290af85c9f0e33c78480656b46bc/packages/react-noop-renderer/src/createReactNoop.js#L82-L285) is flat and doesn't use nested objects. ([@gaearon](https://github.com/gaearon) in [#12792](https://github.com/facebook/react/pull/12792))