useId is a React Hook for generating unique IDs that can be passed to accessibility attributes.

const id = useId()

Reference

useId()

Call useId at the top level of your component to generate a unique ID:

import { useId } from 'react';

function PasswordField() {
  const passwordHintId = useId();
  // ...

See more examples below.

Parameters

useId does not take any parameters.

Returns

useId returns a unique ID string associated with this particular useId call in this particular component.

Caveats

  • useId is a Hook, so you can only call it at the top level of your component or your own Hooks. You can’t call it inside loops or conditions. If you need that, extract a new component and move the state into it.

  • useId should not be used to generate keys in a list. Keys should be generated from your data.

Usage

陷阱

Do not call useId to generate keys in a list. Keys should be generated from your data.

Generating unique IDs for accessibility attributes

Call useId at the top level of your component to generate a unique ID:

import { useId } from 'react';

function PasswordField() {
  const passwordHintId = useId();
  // ...

You can then pass the generated ID to different attributes:

<>
  <input type="password" aria-describedby={passwordHintId} />
  <p id={passwordHintId}>
</>

Let’s walk through an example to see when this is useful.

HTML accessibility attributes like aria-describedby let you specify that two tags are related to each other. For example, you can specify that an element (like an input) is described by another element (like a paragraph).

In regular HTML, you would write it like this:

<label>
  Password:
  <input
    type="password"
    aria-describedby="password-hint"
  />
</label>
<p id="password-hint">
  The password should contain at least 18 characters
</p>

However, hardcoding IDs like this is not a good practice in React. A component may be rendered more than once on the page—but IDs have to be unique! Instead of hardcoding an ID, generate a unique ID with useId:

import { useId } from 'react';

function PasswordField() {
  const passwordHintId = useId();
  return (
    <>
      <label>
        Password:
        <input
          type="password"
          aria-describedby={passwordHintId}
        />
      </label>
      <p id={passwordHintId}>
        The password should contain at least 18 characters
      </p>
    </>
  );
}

Now, even if PasswordField appears multiple times on the screen, the generated IDs won’t clash.

import { useId } from 'react';

function PasswordField() {
  const passwordHintId = useId();
  return (
    <>
      <label>
        Password:
        <input
          type="password"
          aria-describedby={passwordHintId}
        />
      </label>
      <p id={passwordHintId}>
        The password should contain at least 18 characters
      </p>
    </>
  );
}

export default function App() {
  return (
    <>
      <h2>Choose password</h2>
      <PasswordField />
      <h2>Confirm password</h2>
      <PasswordField />
    </>
  );
}

Watch this video to see the difference in the user experience with assistive technologies.

陷阱

With server rendering, useId requires an identical component tree on the server and the client. If the trees you render on the server and the client don’t match exactly, the generated IDs won’t match.

Deep Dive

Why is useId better than an incrementing counter?

You might be wondering why useId is better than incrementing a global variable like nextId++.

The primary benefit of useId is that React ensures that it works with server rendering. During server rendering, your components generate HTML output. Later, on the client, hydration attaches your event handlers to the generated HTML. For hydration to work, the client output must match the server HTML.

This is very difficult to guarantee with an incrementing counter because the order in which the client components are hydrated may not match the order in which the server HTML was emitted. By calling useId, you ensure that hydration will work, and the output will match between the server and the client.

Inside React, useId is generated from the “parent path” of the calling component. This is why, if the client and the server tree are the same, the “parent path” will match up regardless of rendering order.

Generating IDs for several related elements

If you need to give IDs to multiple related elements, you can call useId to generate a shared prefix for them:

import { useId } from 'react';

export default function Form() {
  const id = useId();
  return (
    <form>
      <label htmlFor={id + '-firstName'}>First Name:</label>
      <input id={id + '-firstName'} type="text" />
      <hr />
      <label htmlFor={id + '-lastName'}>Last Name:</label>
      <input id={id + '-lastName'} type="text" />
    </form>
  );
}

This lets you avoid calling useId for every single element that needs a unique ID.

Specifying a shared prefix for all generated IDs

If you render multiple independent React applications on a single page, pass identifierPrefix as an option to your createRoot or hydrateRoot calls. This ensures that the IDs generated by the two different apps never clash because every identifier generated with useId will start with the distinct prefix you’ve specified.

import { createRoot } from 'react-dom/client';
import App from './App.js';
import './styles.css';

const root1 = createRoot(document.getElementById('root1'), {
  identifierPrefix: 'my-first-app-'
});
root1.render(<App />);

const root2 = createRoot(document.getElementById('root2'), {
  identifierPrefix: 'my-second-app-'
});
root2.render(<App />);
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