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useTransition – React

useTransition is a React Hook that lets you render a part of the UI in the background.

const [isPending, startTransition] = useTransition()

• Reference
  • useTransition()
  • startTransition(action)
• Usage
  • Perform non-blocking updates with Actions
  • Exposing action prop from components
  • Displaying a pending visual state
  • Preventing unwanted loading indicators
  • Building a Suspense-enabled router
  • Displaying an error to users with an error boundary
• Troubleshooting
  • Updating an input in a Transition doesn’t work
  • React doesn’t treat my state update as a Transition
  • React doesn’t treat my state update after await as a Transition
  • I want to call useTransition from outside a component
  • The function I pass to startTransition executes immediately
  • My state updates in Transitions are out of order

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

import { useTransition } from 'react';
function TabContainer() {
  const [isPending, startTransition] = useTransition();
  // ...
}

See more examples below.

useTransition does not take any parameters.

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 mark updates as a Transition.

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

function TabContainer() {
  const [isPending, startTransition] = useTransition();
  const [tab, setTab] = useState('about');
  function selectTab(nextTab) {
    startTransition(() => {
      setTab(nextTab);
    });
  }
  // ...
}

The function passed to startTransition is called an “Action”. By convention, any callback called inside startTransition (such as a callback prop) should be named action or include the “Action” suffix:

function SubmitButton({ submitAction }) {
  const [isPending, startTransition] = useTransition();
  return (
    <button
      disabled={isPending}
      onClick={() => {
        startTransition(async () => {
          await submitAction();
        });
      }}
    >
      Submit
    </button>
  );
}

• 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 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 Troubleshooting). State updates marked as Transitions will be non-blocking and will not display unwanted loading indicators.

startTransition does not return anything.

• 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 startTransition 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 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).

• 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. Learn more about removing Effect dependencies.

• 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.

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

import {useState, useTransition} from 'react';
function CheckoutForm() {
  const [isPending, startTransition] = useTransition();
  // ...
}

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:

import {useState, useTransition} from 'react';
import {updateQuantity} from './api';
function CheckoutForm() {
  const [isPending, startTransition] = useTransition();
  const [quantity, setQuantity] = useState(1);
  function onSubmit(newQuantity) {
    startTransition(async function () {
      const savedQuantity = await updateQuantity(newQuantity);
      startTransition(() => {
        setQuantity(savedQuantity);
      });
    });
  }
  // ...
}

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 prevent unwanted loading indicators, and you can provide immediate feedback while the Transition is in progress with useOptimistic.

Example 1 of 2:

In this example, the updateQuantity function simulates a request to the server to update the item’s quantity in the cart. This function is artificially slowed down so that it takes at least a second to complete the request.

Update the quantity multiple times quickly. Notice that the pending “Total” state is shown while any requests are in progress, and the “Total” updates only after the final request is complete. Because the update is in an Action, the “quantity” can continue to be updated while the request is in progress.

import { useState, useTransition } from "react";
import { updateQuantity } from "./api";
import Item from "./Item";
import Total from "./Total";

export default function App({}) {
  const [quantity, setQuantity] = useState(1);
  const [isPending, startTransition] = useTransition();

  const updateQuantityAction = async newQuantity => {
    // To access the pending state of a transition,
    // call startTransition again.
    startTransition(async () => {
      const savedQuantity = await updateQuantity(newQuantity);
      startTransition(() => {
        setQuantity(savedQuantity);
      });
    });
  };

  return (
    <div>
      <h1>Checkout</h1>
      <Item action={updateQuantityAction}/>
      <hr />
      <Total quantity={quantity} isPending={isPending} />
    </div>
  );
}

This is a basic example to demonstrate how Actions work, but this example does not handle requests completing out of order. When updating the quantity multiple times, it’s possible for the previous requests to finish after later requests causing the quantity to update out of order. This is a known limitation that we will fix in the future (see Troubleshooting below).

For common use cases, React provides built-in abstractions such as:

• useActionState
• <form> actions
• Server Functions

These solutions handle request ordering for you. When using Transitions to build your own custom hooks or libraries that manage async state transitions, you have greater control over the request ordering, but you must handle it yourself.

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:

export default function TabButton({ action, children, isActive }) {
  const [isPending, startTransition] = useTransition();
  if (isActive) {
    return <b>{children}</b>
  }
  return (
    <button onClick={() => {
      startTransition(async () => {
        // await the action that's passed in.
        // This allows it to be either sync or async. 
        await action();
      });
    }}>
      {children}
    </button>
  );
}

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:

import { useTransition } from 'react';

export default function TabButton({ action, children, isActive }) {
  const [isPending, startTransition] = useTransition();
  if (isActive) {
    return <b>{children}</b>
  }
  if (isPending) {
    return <b className="pending">{children}</b>;
  }
  return (
    <button onClick={async () => {
      startTransition(async () => {
        // await the action that's passed in.
        // This allows it to be either sync or async. 
        await action();
      });
    }}>
      {children}
    </button>
  );
}

When exposing an action prop from a component, you should await it inside the transition.

This allows the action callback to be either synchronous or asynchronous without requiring an additional startTransition to wrap the await in the action.

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:

function TabButton({ action, children, isActive }) {
  const [isPending, startTransition] = useTransition();
  // ...
  if (isPending) {
    return <b className="pending">{children}</b>;
  }
  // ...

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

import { useTransition } from 'react';

export default function TabButton({ action, children, isActive }) {
  const [isPending, startTransition] = useTransition();
  if (isActive) {
    return <b>{children}</b>
  }
  if (isPending) {
    return <b className="pending">{children}</b>;
  }
  return (
    <button onClick={() => {
      startTransition(async () => {
        await action();
      });
    }}>
      {children}
    </button>
  );
}

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

import { Suspense, useState } from 'react';
import TabButton from './TabButton.js';
import AboutTab from './AboutTab.js';
import PostsTab from './PostsTab.js';
import ContactTab from './ContactTab.js';

export default function TabContainer() {
  const [tab, setTab] = useState('about');
  return (
    <Suspense fallback={<h1>🌀 Loading...</h1>}>
      <TabButton
        isActive={tab === 'about'}
        action={() => setTab('about')}
      >
        About
      </TabButton>
      <TabButton
        isActive={tab === 'posts'}
        action={() => setTab('posts')}
      >
        Posts
      </TabButton>
      <TabButton
        isActive={tab === 'contact'}
        action={() => setTab('contact')}
      >
        Contact
      </TabButton>
      <hr />
      {tab === 'about' && <AboutTab />}
      {tab === 'posts' && <PostsTab />}
      {tab === 'contact' && <ContactTab />}
    </Suspense>
  );
}

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:

import { useTransition } from 'react';

export default function TabButton({ action, children, isActive }) {
  const [isPending, startTransition] = useTransition();
  if (isActive) {
    return <b>{children}</b>
  }
  if (isPending) {
    return <b className="pending">{children}</b>;
  }
  return (
    <button onClick={() => {
      startTransition(async () => {
        await action();
      });
    }}>
      {children}
    </button>
  );
}

Read more about using Transitions with Suspense.

Transitions only “wait” long enough to avoid hiding already revealed content (like the tab container). If the Posts tab had a nested <Suspense> boundary, the Transition would not “wait” for it.

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

function Router() {
  const [page, setPage] = useState('/');
  const [isPending, startTransition] = useTransition();
  function navigate(url) {
    startTransition(() => {
      setPage(url);
    });
  }
  // ...

This is recommended for three reasons:

• Transitions are interruptible, which lets the user click away without waiting for the re-render to complete.
• Transitions prevent unwanted loading indicators, which lets the user avoid jarring jumps on navigation.
• Transitions wait for all pending actions 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.

import { Suspense, useState, useTransition } from 'react';
import IndexPage from './IndexPage.js';
import ArtistPage from './ArtistPage.js';
import Layout from './Layout.js';

export default function App() {
  return (
    <Suspense fallback={<BigSpinner />}>
      <Router />
    </Suspense>
  );
}

function Router() {
  const [page, setPage] = useState('/');
  const [isPending, startTransition] = useTransition();

  function navigate(url) {
    startTransition(() => {
      setPage(url);
    });
  }

  let content;
  if (page === '/') {
    content = (
      <IndexPage navigate={navigate} />
    );
  } else if (page === '/the-beatles') {
    content = (
      <ArtistPage
        artist={{
          id: 'the-beatles',
          name: 'The Beatles',
        }}
      />
    );
  }
  return (
    <Layout isPending={isPending}>
      {content}
    </Layout>
  );
}

function BigSpinner() {
  return <h2>🌀 Loading...</h2>;
}

Suspense-enabled routers are expected to wrap the navigation updates into Transitions by default.

If a function passed to startTransition throws an error, you can display an error to your user with an error boundary. 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.

import { useTransition } from "react";
import { ErrorBoundary } from "react-error-boundary";

export function AddCommentContainer() {
  return (
    <ErrorBoundary fallback={<p>⚠️Something went wrong</p>}>
      <AddCommentButton />
    </ErrorBoundary>
  );
}

function addComment(comment) {
  // For demonstration purposes to show Error Boundary
  if (comment == null) {
    throw new Error("Example Error: An error thrown to trigger error boundary");
  }
}

function AddCommentButton() {
  const [pending, startTransition] = useTransition();

  return (
    <button
      disabled={pending}
      onClick={() => {
        startTransition(() => {
          // Intentionally not passing a comment
          // so error gets thrown
          addComment();
        });
      }}
    >
      Add comment
    </button>
  );
}

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

const [text, setText] = useState('');
// ...
function handleChange(e) {
  // ❌ Can't use Transitions for controlled input state
  startTransition(() => {
    setText(e.target.value);
  });
}
// ...
return <input value={text} onChange={handleChange} />;

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 useDeferredValue which will “lag behind” the real value. It will trigger non-blocking re-renders to “catch up” with the new value automatically.

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

startTransition(() => {
  // ✅ Setting state *during* startTransition call
  setPage('/about');
});

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

startTransition(() => {
  // ❌ Setting state *after* startTransition call
  setTimeout(() => {
    setPage('/about');
  }, 1000);
});

Instead, you could do this:

setTimeout(() => {
  startTransition(() => {
    // ✅ Setting state *during* startTransition call
    setPage('/about');
  });
}, 1000);

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:

startTransition(async () => {
  await someAsyncFunction();
  // ❌ Not using startTransition after await
  setPage('/about');
});

However, this works instead:

startTransition(async () => {
  await someAsyncFunction();
  // ✅ Using startTransition *after* await
  startTransition(() => {
    setPage('/about');
  });
});

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

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

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

console.log(1);
startTransition(() => {
  console.log(2);
  setPage('/about');
});
console.log(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:

// A simplified version of how React works
let isInsideTransition = false;
function startTransition(scope) {
  isInsideTransition = true;
  scope();
  isInsideTransition = false;
}
function setState() {
  if (isInsideTransition) {
    // ... schedule a Transition state update ...
  } else {
    // ... schedule an urgent state update ...
  }
}

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:

import { useState, useTransition } from "react";
import { updateQuantity } from "./api";
import Item from "./Item";
import Total from "./Total";

export default function App({}) {
  const [quantity, setQuantity] = useState(1);
  const [isPending, startTransition] = useTransition();
  // Store the actual quantity in separate state to show the mismatch.
  const [clientQuantity, setClientQuantity] = useState(1);
  
  const updateQuantityAction = newQuantity => {
    setClientQuantity(newQuantity);

    // Access the pending state of the transition,
    // by wrapping in startTransition again.
    startTransition(async () => {
      const savedQuantity = await updateQuantity(newQuantity);
      startTransition(() => {
        setQuantity(savedQuantity);
      });
    });
  };

  return (
    <div>
      <h1>Checkout</h1>
      <Item action={updateQuantityAction}/>
      <hr />
      <Total clientQuantity={clientQuantity} savedQuantity={quantity} isPending={isPending} />
    </div>
  );
}

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 useActionState and <form> actions 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:

import { useState, useActionState } from "react";
import { updateQuantity } from "./api";
import Item from "./Item";
import Total from "./Total";

export default function App({}) {
  // Store the actual quantity in separate state to show the mismatch.
  const [clientQuantity, setClientQuantity] = useState(1);
  const [quantity, updateQuantityAction, isPending] = useActionState(
    async (prevState, payload) => {
      setClientQuantity(payload);
      const savedQuantity = await updateQuantity(payload);
      return savedQuantity; // Return the new quantity to update the state
    },
    1 // Initial quantity
  );

  return (
    <div>
      <h1>Checkout</h1>
      <Item action={updateQuantityAction}/>
      <hr />
      <Total clientQuantity={clientQuantity} savedQuantity={quantity} isPending={isPending} />
    </div>
  );
}

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