Refs ed il DOM

Refs provide a way to access DOM nodes or React elements created in the render method.

In the typical React dataflow, props are the only way that parent components interact with their children. To modify a child, you re-render it with new props. However, there are a few cases where you need to imperatively modify a child outside of the typical dataflow. The child to be modified could be an instance of a React component, or it could be a DOM element. For both of these cases, React provides an escape hatch.

When to Use Refs

There are a few good use cases for refs:

• Managing focus, text selection, or media playback.
• Triggering imperative animations.
• Integrating with third-party DOM libraries.

Avoid using refs for anything that can be done declaratively.

For example, instead of exposing open() and close() methods on a Dialog component, pass an isOpen prop to it.

Don’t Overuse Refs

Your first inclination may be to use refs to “make things happen” in your app. If this is the case, take a moment and think more critically about where state should be owned in the component hierarchy. Often, it becomes clear that the proper place to “own” that state is at a higher level in the hierarchy. See the Lifting State Up guide for examples of this.

Note

The examples below have been updated to use the React.createRef() API introduced in React 16.3. If you are using an earlier release of React, we recommend using callback refs instead.

Creating Refs

Refs are created using React.createRef() and attached to React elements via the ref attribute. Refs are commonly assigned to an instance property when a component is constructed so they can be referenced throughout the component.

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.myRef = React.createRef();  }
  render() {
    return <div ref={this.myRef} />;  }
}

Accessing Refs

When a ref is passed to an element in render, a reference to the node becomes accessible at the current attribute of the ref.

const node = this.myRef.current;

The value of the ref differs depending on the type of the node:

• When the ref attribute is used on an HTML element, the ref created in the constructor with React.createRef() receives the underlying DOM element as its current property.
• When the ref attribute is used on a custom class component, the ref object receives the mounted instance of the component as its current.
• You may not use the ref attribute on function components because they don’t have instances.

The examples below demonstrate the differences.

Adding a Ref to a DOM Element

This code uses a ref to store a reference to a DOM node:

class CustomTextInput extends React.Component {
  constructor(props) {
    super(props);
    // create a ref to store the textInput DOM element
    this.textInput = React.createRef();    this.focusTextInput = this.focusTextInput.bind(this);
  }

  focusTextInput() {
    // Explicitly focus the text input using the raw DOM API
    // Note: we're accessing "current" to get the DOM node
    this.textInput.current.focus();  }

  render() {
    // tell React that we want to associate the <input> ref
    // with the `textInput` that we created in the constructor
    return (
      <div>
        <input
          type="text"
          ref={this.textInput} />        <input
          type="button"
          value="Focus the text input"
          onClick={this.focusTextInput}
        />
      </div>
    );
  }
}

React will assign the current property with the DOM element when the component mounts, and assign it back to null when it unmounts. ref updates happen before componentDidMount or componentDidUpdate lifecycle methods.

Adding a Ref to a Class Component

If we wanted to wrap the CustomTextInput above to simulate it being clicked immediately after mounting, we could use a ref to get access to the custom input and call its focusTextInput method manually:

class AutoFocusTextInput extends React.Component {
  constructor(props) {
    super(props);
    this.textInput = React.createRef();  }

  componentDidMount() {
    this.textInput.current.focusTextInput();  }

  render() {
    return (
      <CustomTextInput ref={this.textInput} />    );
  }
}

Note that this only works if CustomTextInput is declared as a class:

class CustomTextInput extends React.Component {  // ...
}

Refs and Function Components

By default, you may not use the ref attribute on function components because they don’t have instances:

function MyFunctionComponent() {  return <input />;
}

class Parent extends React.Component {
  constructor(props) {
    super(props);
    this.textInput = React.createRef();  }
  render() {
    // This will *not* work!
    return (
      <MyFunctionComponent ref={this.textInput} />    );
  }
}

If you want to allow people to take a ref to your function component, you can use forwardRef (possibly in conjunction with useImperativeHandle), or you can convert the component to a class.

You can, however, use the ref attribute inside a function component as long as you refer to a DOM element or a class component:

function CustomTextInput(props) {
  // textInput must be declared here so the ref can refer to it  const textInput = useRef(null);  
  function handleClick() {
    textInput.current.focus();  }

  return (
    <div>
      <input
        type="text"
        ref={textInput} />      <input
        type="button"
        value="Focus the text input"
        onClick={handleClick}
      />
    </div>
  );
}

Exposing DOM Refs to Parent Components

In rare cases, you might want to have access to a child’s DOM node from a parent component. This is generally not recommended because it breaks component encapsulation, but it can occasionally be useful for triggering focus or measuring the size or position of a child DOM node.

While you could add a ref to the child component, this is not an ideal solution, as you would only get a component instance rather than a DOM node. Additionally, this wouldn’t work with function components.

If you use React 16.3 or higher, we recommend to use ref forwarding for these cases. Ref forwarding lets components opt into exposing any child component’s ref as their own. You can find a detailed example of how to expose a child’s DOM node to a parent component in the ref forwarding documentation.

If you use React 16.2 or lower, or if you need more flexibility than provided by ref forwarding, you can use this alternative approach and explicitly pass a ref as a differently named prop.

When possible, we advise against exposing DOM nodes, but it can be a useful escape hatch. Note that this approach requires you to add some code to the child component. If you have absolutely no control over the child component implementation, your last option is to use findDOMNode(), but it is discouraged and deprecated in StrictMode.

Callback Refs

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.

Legacy API: String Refs

If you worked with React before, you might be familiar with an older API where the ref attribute is a string, like "textInput", and the DOM node is accessed as this.refs.textInput. We advise against it because string refs have some issues, are considered legacy, and are likely to be removed in one of the future releases.

Note

If you’re currently using this.refs.textInput to access refs, we recommend using either the callback pattern or the createRef API instead.

Caveats with callback refs

If the ref callback is defined as an inline function, it will get called twice during updates, first with null and then again with the DOM element. This is because a new instance of the function is created with each render, so React needs to clear the old ref and set up the new one. You can avoid this by defining the ref callback as a bound method on the class, but note that it shouldn’t matter in most cases.