useTransition

Reference

useTransition()

Call useTransition at the top level of your component to mark some state updates as Transitions.

Parameters

useTransition does not take any parameters.

Returns

useTransition returns an array with exactly two items:

1. The isPending flag that tells you whether there is a pending Transition.
2. The that lets you mark updates as a Transition.

startTransition(action)

The startTransition function returned by useTransition lets you mark an update as a Transition.

Parameters

• action: A function that updates some state by calling one or more . React calls action immediately with no parameters and marks all state updates scheduled synchronously during the action function call as Transitions. Any async calls that are 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 ). State updates marked as Transitions will be and .

Returns

startTransition does not return anything.

Caveats

• useTransition is a Hook, so it can only be called inside components or custom Hooks. If you need to start a Transition somewhere else (for example, from a data library), call the standalone 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 value, try 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 ).

• The startTransition function has a stable identity, so you will often see it omitted from Effect dependencies, but including it will not cause the Effect to fire. If the linter lets you omit a dependency without errors, it is safe to do.

• 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 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

Perform non-blocking updates with Actions

Call useTransition at the top of your component to create Actions, and access the pending state:

useTransition returns an array with exactly two items:

1. The isPending flag that tells you whether there is a pending Transition.
2. The startTransition function that lets you create an Action.

To start a Transition, pass a function to startTransition like this:

The function passed to startTransition is called the “Action”. You can update state and (optionally) perform side effects within an Action, and the work will be done in the background without blocking user interactions on the page. A Transition can include multiple Actions, and while a Transition is in progress, your UI stays responsive. For example, if the user clicks a tab but then changes their mind and clicks another tab, the second click will be immediately handled without waiting for the first update to finish.

To give the user feedback about in-progress Transitions, the isPending state switches to true at the first call to startTransition, and stays true until all Actions complete and the final state is shown to the user. Transitions ensure side effects in Actions to complete in order to , and you can provide immediate feedback while the Transition is in progress with useOptimistic.

Exposing action prop from components

You can expose an action prop from a component to allow a parent to call an Action.

For example, this TabButton component wraps its onClick logic in an action prop:

Because the parent component updates its state inside the action, that state update gets marked as a Transition. This means you can click on “Posts” and then immediately click “Contact” and it does not block user interactions:

Displaying a pending visual state

You can use the isPending boolean value returned by useTransition to indicate to the user that a Transition is in progress. For example, the tab button can have a special “pending” visual state:

Notice how clicking “Posts” now feels more responsive because the tab button itself updates right away:

Preventing unwanted loading indicators

In this example, the PostsTab component fetches some data using . When you click the “Posts” tab, the PostsTab component suspends, causing the closest loading fallback to appear:

Hiding the entire tab container to show a loading indicator leads to a jarring user experience. If you add useTransition to TabButton, you can instead display the pending state in the tab button instead.

Notice that clicking “Posts” no longer replaces the entire tab container with a spinner:

Building a Suspense-enabled router

If you’re building a React framework or a router, we recommend marking page navigations as Transitions.

This is recommended for three reasons:

• which lets the user click away without waiting for the re-render to complete.
• which lets the user avoid jarring jumps on navigation.
• which lets the user wait for side effects to complete before the new page is shown.

Here is a simplified router example using Transitions for navigations.

Displaying an error to users with an error boundary

If a function passed to startTransition throws an error, you can display an error to your user with an . To use an error boundary, wrap the component where you are calling the useTransition in an error boundary. Once the function passed to startTransition errors, the fallback for the error boundary will be displayed.

Troubleshooting

Updating an input in a Transition doesn’t work

You can’t use a Transition for a state variable that controls an input:

This is because Transitions are non-blocking, but updating an input in response to the change event should happen synchronously. If you want to run a Transition in response to typing, you have two options:

1. You can declare two separate state variables: one for the input state (which always updates synchronously), and one that you will update in a Transition. This lets you control the input using the synchronous state, and pass the Transition state variable (which will “lag behind” the input) to the rest of your rendering logic.
2. Alternatively, you can have one state variable, and add which will “lag behind” the real value. It will trigger non-blocking re-renders to “catch up” with the new value automatically.

React doesn’t treat my state update as a Transition

When you wrap a state update in a Transition, make sure that it happens during the startTransition call:

The function you pass to startTransition must be synchronous. You can’t mark an update as a Transition like this:

Instead, you could do this:

React doesn’t treat my state update after await as a Transition

When you use await inside a startTransition function, the state updates that happen after the await are not marked as Transitions. You must wrap state updates after each await in a startTransition call:

However, this works instead:

This is a JavaScript limitation due to React losing the scope of the async context. In the future, when is available, this limitation will be removed.

I want to call useTransition from outside a component

You can’t call useTransition outside a component because it’s a Hook. In this case, use the standalone method instead. It works the same way, but it doesn’t provide the isPending indicator.

The function I pass to startTransition executes immediately

If you run this code, it will print 1, 2, 3:

It is expected to print 1, 2, 3. The function you pass to startTransition does not get delayed. Unlike with the browser setTimeout, it does not run the callback later. React executes your function immediately, but any state updates scheduled while it is running are marked as Transitions. You can imagine that it works like this:

My state updates in Transitions are out of order

If you await inside startTransition, you might see the updates happen out of order.

In this example, the updateQuantity function simulates a request to the server to update the item’s quantity in the cart. This function artificially returns the every other request after the previous to simulate race conditions for network requests.

Try updating the quantity once, then update it quickly multiple times. You might see the incorrect total:

When clicking multiple times, it’s possible for previous requests to finish after later requests. When this happens, React currently has no way to know the intended order. This is because the updates are scheduled asynchronously, and React loses context of the order across the async boundary.

This is expected, because Actions within a Transition do not guarantee execution order. For common use cases, React provides higher-level abstractions like and that handle ordering for you. For advanced use cases, you’ll need to implement your own queuing and abort logic to handle this.

Example of useActionState handling execution order: