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React also supports another way to set refs called “callback refs”, which gives more fine-grain control over when refs are set and unset.
Instead of passing a ref attribute created by createRef(), you pass a function. The function receives the React component instance or HTML DOM element as its argument, which can be stored and accessed elsewhere.
The example below implements a common pattern: using the ref callback to store a reference to a DOM node in an instance property.
class CustomTextInput extends React.Component {
constructor(props) {
super(props);
this.textInput = null;
this.setTextInputRef = element => {
this.textInput = element;
};
this.focusTextInput = () => {
// Focus the text input using the raw DOM API
if (this.textInput) this.textInput.focus();
};
}
componentDidMount() {
// autofocus the input on mount
this.focusTextInput();
}
render() {
// Use the `ref` callback to store a reference to the text input DOM
// element in an instance field (for example, this.textInput).
return (
<div>
<input
type=”text”
ref={this.setTextInputRef}
/>
<input
type=”button”
value=”Focus the text input”
onClick={this.focusTextInput}
/>
</div>
);
}
}
React will call the ref callback with the DOM element when the component mounts, and call it with null when it unmounts. Refs are guaranteed to be up-to-date before componentDidMount or componentDidUpdate fires.
You can pass callback refs between components like you can with object refs that were created with React.createRef().
function CustomTextInput(props) {
return (
<div>
<input ref={props.inputRef} />
</div>
);
}
class Parent extends React.Component {
render() {
return (
<CustomTextInput
inputRef={el => this.inputElement = el}
/>
);
}
}
In the example above, Parent passes its ref callback as an inputRef prop to the CustomTextInput, and the CustomTextInput passes the same function as a special ref attribute to the <input>. As a result, this.inputElement in Parent will be set to the DOM node corresponding to the <input> element in the CustomTextInput.
