Resources for React Fiber
Switch branches/tags
Nothing to show
Clone or download

React Fiber resources PRs Welcome

This is a repository of resources for React Fiber.

React Fiber is a new React reconciler algorithm, which is used from v16.

Try React Fiber asynchronous rendering!

You can try React Fiber asynchronous rendering by the following ways.

1. Use ReactDOM.unstable_deferredUpdates

Inside a ReactDOM.unstable_deferredUpdates callback, the updates are treated as Low Priority.

ReactDOM.unstable_deferredUpdates(() => {
    ReactDOM.render(<App />. container);
    // or
    instance.setState(() => newState);

2. Use React.unstable_AsyncMode

React.unstable_AsyncMode is a Component to make updates in child components asynchronous, which means the updates are treated as Low Priority.

const AsyncMode = React.unstable_AsyncMode;

  <App /> // Low Priority by default

If you'd like to use synchronous updates inside the component, you can use ReactDOM.flushSync(cb). Inside of the ReactDOM.flushSync callback, the updates are treated as Sync Priority, which is the default priority of v16.

ReactDOM.flushSync(() => {
    // Sync Priority for use input or an animation etc


You can try the React Fiber's time slicing feature in the following example. In the example, you would realize that low priorities updates don't block sync priority updates. If you can't get any diferrence between Async mode and Sync mode, you should use CPU throttling on Chrome 😄

How to contribute React Fiber

React internal algorithm

If you are not familiar with React internals, I recommend you to read the documentations, which are very helpful.

React Fiber

Articles & Slides


React Fiber function call stacks

[Note] React Fiber now behaves as synchronous by default. See #8127. This call stacks are results in the time when it behaved as asynchronous.


React Fiber function call stack


ReactDOM function call stack

ReactDOMFiber with 10000 items (Async Scheduling)

React Fiber function call stack with 10000 items (async)

--- working asynchronously using requestIdleCallback -------------------------------------------------
| ------- Fiber ---------------    ------- Fiber ---------------    ------ Fiber ---------------     |
| | beginWork -> completeWork | -> | beginWork -> completeWork | -> |beginWork -> completeWork | ... |
| -----------------------------   ------------------------------    ----------------------------     |
| commitAllWork(flush side effects computed in the above to the host) |

ReactDOMFiber with 10000 items (Sync Scheduling)

React Fiber function call stack with 10000 items (sync)

ReactDOM with 10000 items

ReactDOMFiber function call stack with 10000 items

React Fiber call tree

ReactDOMFiber call tree

Related Words

Custom Renderer Interface

You should implement the following interface when create a custom fiber renderer.

Toy custom renderers

    <rainbow>Custom Renderer!</rainbow>
  () => console.log(colors.inverse('##### Update ######'))
  • Voice Renderer
        <victoria>React Fiber</victoria>


ReactNoop is a renderer for React Fiber, which is using for testing and debugging. It is very useful to understand React Fiber renderer!! 👀

Bonus: You should watch ReactIncremental-test.internal.js, which helps to understand what React Fiber makes it possible