startTransition

startTransition(action)

• Reference
  • startTransition(action)
• Usage
  • Marking a state update as a non-blocking Transition

Reference

startTransition(action)

The startTransition function lets you mark a state update as a Transition.

import { startTransition } from 'react';

function TabContainer() {
  const [tab, setTab] = useState('about');

  function selectTab(nextTab) {
    startTransition(() => {
      setTab(nextTab);
    });
  }
  // ...
}

See more examples below.

Parameters

• action: A function that updates some state by calling one or more set functions. React calls action immediately with no parameters and marks all state updates scheduled synchronously during the action function call as Transitions. Any async calls awaited in the action will be included in the transition, but currently require wrapping any set functions after the await in an additional startTransition (see Troubleshooting). State updates marked as Transitions will be non-blocking and will not display unwanted loading indicators..

Returns

startTransition does not return anything.

Caveats

• startTransition does not provide a way to track whether a Transition is pending. To show a pending indicator while the Transition is ongoing, you need useTransition instead.

• You can wrap an update into a Transition only if you have access to the set function of that state. If you want to start a Transition in response to some prop or a custom Hook return value, try useDeferredValue instead.

• The function you pass to startTransition is called immediately, marking all state updates that happen while it executes as Transitions. If you try to perform state updates in a setTimeout, for example, they won’t be marked as Transitions.

• You must wrap any state updates after any async requests in another startTransition to mark them as Transitions. This is a known limitation that we will fix in the future (see Troubleshooting).

• A state update marked as a Transition will be interrupted by other state updates. For example, if you update a chart component inside a Transition, but then start typing into an input while the chart is in the middle of a re-render, React will restart the rendering work on the chart component after handling the input state update.

• Transition updates can’t be used to control text inputs.

• If there are multiple ongoing Transitions, React currently batches them together. This is a limitation that may be removed in a future release.

Usage

Marking a state update as a non-blocking Transition

You can mark a state update as a Transition by wrapping it in a startTransition call:

import { startTransition } from 'react';

function TabContainer() {
  const [tab, setTab] = useState('about');

  function selectTab(nextTab) {
    startTransition(() => {
      setTab(nextTab);
    });
  }
  // ...
}

Transitions let you keep the user interface updates responsive even on slow devices.

With a Transition, your UI stays responsive in the middle of a re-render. For example, if the user clicks a tab but then change their mind and click another tab, they can do that without waiting for the first re-render to finish.