The methods you expose via an imperative handle don't have to match the DOM methods exactly. For example, the `Post` component in the example below exposes a `scrollAndFocusAddComment` method via an imperative handle. This lets the parent `Page` scroll the list of comments *and* focus the input field when you click the button:
<Sandpack>
```js
import { useRef } from 'react';
import Post from './Post.js';
export default function Page() {
const postRef = useRef(null);
function handleClick() {
postRef.current.scrollAndFocusAddComment();
}
return (
<>
<buttononClick={handleClick}>
Write a comment
</button>
<Postref={postRef}/>
</>
);
}
```
```js Post.js
import { forwardRef, useRef, useImperativeHandle } from 'react';
import CommentList from './CommentList.js';
import AddComment from './AddComment.js';
const Post = forwardRef((props, ref) => {
const commentsRef = useRef(null);
const addCommentRef = useRef(null);
useImperativeHandle(ref, () => {
return {
scrollAndFocusAddComment() {
commentsRef.current.scrollToBottom();
addCommentRef.current.focus();
}
};
}, []);
return (
<>
<article>
<p>Welcome to my blog!</p>
</article>
<CommentListref={commentsRef}/>
<AddCommentref={addCommentRef}/>
</>
);
});
export default Post;
```
```js CommentList.js
import { forwardRef, useRef, useImperativeHandle } from 'react';
### Exposing a custom ref handle to the parent component {/*exposing-a-custom-ref-handle-to-the-parent-component*/}
By default, components don't expose their DOM nodes to parent components. For example, if you want the parent component of `MyInput` to [have access](/learn/manipulating-the-dom-with-refs) to the `<input>` DOM node, you have to opt in with [`forwardRef`:](/apis/react/forwardRef)
With the code above, [a ref to `MyInput` will receive the `<input>` DOM node.](/apis/react/forwardRef#exposing-a-dom-node-to-the-parent-component) However, you can expose a custom value instead. To customize the exposed handle, call `useImperativeHandle` at the top level of your component:
```js {4-8}
import { forwardRef, useImperativeHandle } from 'react';
Note that in the code above, the `ref` is no longer forwarded to the `<input>`.
For example, suppose you don't want to expose the entire `<input>` DOM node, but you want to expose two of its methods: `focus` and `scrollIntoView`. To do this, keep the real browser DOM in a separate ref. Then use `useImperativeHandle` to expose a handle with only the methods that you want the parent component to call:
```js {7-14}
import { forwardRef, useRef, useImperativeHandle } from 'react';
Now, if the parent component gets a ref to `MyInput`, it will be able to call the `focus` and `scrollIntoView` methods on it. However, it will not have full access to the underlying `<input>` DOM node.
<Sandpack>
```js
useImperativeHandle(ref, createHandle, [deps])
import { useRef } from 'react';
import MyInput from './MyInput.js';
export default function Form() {
const ref = useRef(null);
function handleClick() {
ref.current.focus();
// This won't work because the DOM node isn't exposed:
// ref.current.style.opacity = 0.5;
}
return (
<form>
<MyInputlabel="Enter your name:"ref={ref}/>
<buttontype="button"onClick={handleClick}>
Edit
</button>
</form>
);
}
```
</Intro>
```js MyInput.js
import { forwardRef, useRef, useImperativeHandle } from 'react';
### Exposing your own imperative methods {/*exposing-your-own-imperative-methods*/}
The methods you expose via an imperative handle don't have to match the DOM methods exactly. For example, the `Post` component in the example below exposes a `scrollAndFocusAddComment` method via an imperative handle. This lets the parent `Page` scroll the list of comments *and* focus the input field when you click the button:
<Sandpack>
```js
import { useRef } from 'react';
import Post from './Post.js';
export default function Page() {
const postRef = useRef(null);
function handleClick() {
postRef.current.scrollAndFocusAddComment();
}
return (
<>
<buttononClick={handleClick}>
Write a comment
</button>
<Postref={postRef}/>
</>
);
}
```
```js Post.js
import { forwardRef, useRef, useImperativeHandle } from 'react';
import CommentList from './CommentList.js';
import AddComment from './AddComment.js';
const Post = forwardRef((props, ref) => {
const commentsRef = useRef(null);
const addCommentRef = useRef(null);
useImperativeHandle(ref, () => {
return {
scrollAndFocusAddComment() {
commentsRef.current.scrollToBottom();
addCommentRef.current.focus();
}
};
}, []);
return (
<>
<article>
<p>Welcome to my blog!</p>
</article>
<CommentListref={commentsRef}/>
<AddCommentref={addCommentRef}/>
</>
);
});
export default Post;
```
```js CommentList.js
import { forwardRef, useRef, useImperativeHandle } from 'react';
**Do not overuse refs.** You should only use refs for *imperative* behaviors that you can't express as props: for example, scrolling to a node, focusing a node, triggering an animation, selecting text, and so on.
**If you can express something as a prop, you should not use a ref.** For example, instead of exposing an imperative handle like `{ open, close }` from a `Modal` component, it is better to take `isOpen` as a prop like `<Modal isOpen={isOpen} />`. [Effects](/learn/synchronizing-with-effects) can help you expose imperative behaviors via props.
* `ref`: The `ref` you received as the second argument from the [`forwardRef` render function.](/apis/react/forwardRef#render-function)
* `createHandle`: A function that takes no arguments and returns the ref handle you want to expose. The ref handle you return have any type. Usually, you will return an object with the methods you want to expose.
* **optional**`dependencies`: The list of all reactive values referenced inside of the `createHandle` code. Reactive values include props, state, and all the variables and functions declared directly inside your component body. If your linter is [configured for React](/learn/editor-setup#linting), it will verify that every reactive value is correctly specified as a dependency. The list of dependencies must have a constant number of items and be written inline like `[dep1, dep2, dep3]`. React will compare each dependency with its previous value using the [`Object.is`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is) comparison algorithm. If a re-render resulted in a change to some dependency, or if you did not specify the dependencies at all, your `createHandle` function will re-execute, and the newly created handle will be assigned to the ref.
dan
2 years ago
GitHub