Inoltrare Refs

Ref forwarding is a technique for automatically passing a ref through a component to one of its children. This is typically not necessary for most components in the application. However, it can be useful for some kinds of components, especially in reusable component libraries. The most common scenarios are described below.

Forwarding refs to DOM components

Consider a FancyButton component that renders the native button DOM element:

function FancyButton(props) {
  return (
    <button className="FancyButton">
      {props.children}
    </button>
  );
}

React components hide their implementation details, including their rendered output. Other components using FancyButton usually will not need to obtain a ref to the inner button DOM element. This is good because it prevents components from relying on each other’s DOM structure too much.

Although such encapsulation is desirable for application-level components like FeedStory or Comment, it can be inconvenient for highly reusable “leaf” components like FancyButton or MyTextInput. These components tend to be used throughout the application in a similar manner as a regular DOM button and input, and accessing their DOM nodes may be unavoidable for managing focus, selection, or animations.

Ref forwarding is an opt-in feature that lets some components take a ref they receive, and pass it further down (in other words, “forward” it) to a child.

In the example below, FancyButton uses React.forwardRef to obtain the ref passed to it, and then forward it to the DOM button that it renders:

const FancyButton = React.forwardRef((props, ref) => (  <button ref={ref} className="FancyButton">    {props.children}
  </button>
));

// You can now get a ref directly to the DOM button:
const ref = React.createRef();
<FancyButton ref={ref}>Click me!</FancyButton>;

This way, components using FancyButton can get a ref to the underlying button DOM node and access it if necessary—just like if they used a DOM button directly.

Here is a step-by-step explanation of what happens in the above example:

1. We create a React ref by calling React.createRef and assign it to a ref variable.
2. We pass our ref down to <FancyButton ref={ref}> by specifying it as a JSX attribute.
3. React passes the ref to the (props, ref) => ... function inside forwardRef as a second argument.
4. We forward this ref argument down to <button ref={ref}> by specifying it as a JSX attribute.
5. When the ref is attached, ref.current will point to the <button> DOM node.

Note

The second ref argument only exists when you define a component with React.forwardRef call. Regular function or class components don’t receive the ref argument, and ref is not available in props either.

Ref forwarding is not limited to DOM components. You can forward refs to class component instances, too.

Note for component library maintainers

When you start using forwardRef in a component library, you should treat it as a breaking change and release a new major version of your library. This is because your library likely has an observably different behavior (such as what refs get assigned to, and what types are exported), and this can break apps and other libraries that depend on the old behavior.

Conditionally applying React.forwardRef when it exists is also not recommended for the same reasons: it changes how your library behaves and can break your users’ apps when they upgrade React itself.

Forwarding refs in higher-order components

This technique can also be particularly useful with higher-order components (also known as HOCs). Let’s start with an example HOC that logs component props to the console:

function logProps(WrappedComponent) {  class LogProps extends React.Component {
    componentDidUpdate(prevProps) {
      console.log('old props:', prevProps);
      console.log('new props:', this.props);
    }

    render() {
      return <WrappedComponent {...this.props} />;    }
  }

  return LogProps;
}

The “logProps” HOC passes all props through to the component it wraps, so the rendered output will be the same. For example, we can use this HOC to log all props that get passed to our “fancy button” component:

class FancyButton extends React.Component {
  focus() {
    // ...
  }

  // ...
}

// Rather than exporting FancyButton, we export LogProps.
// It will render a FancyButton though.
export default logProps(FancyButton);

There is one caveat to the above example: refs will not get passed through. That’s because ref is not a prop. Like key, it’s handled differently by React. If you add a ref to a HOC, the ref will refer to the outermost container component, not the wrapped component.

This means that refs intended for our FancyButton component will actually be attached to the LogProps component:

import FancyButton from './FancyButton';

const ref = React.createRef();
// The FancyButton component we imported is the LogProps HOC.
// Even though the rendered output will be the same,
// Our ref will point to LogProps instead of the inner FancyButton component!
// This means we can't call e.g. ref.current.focus()
<FancyButton
  label="Click Me"
  handleClick={handleClick}
  ref={ref}/>;

Fortunately, we can explicitly forward refs to the inner FancyButton component using the React.forwardRef API. React.forwardRef accepts a render function that receives props and ref parameters and returns a React node. For example:

function logProps(Component) {
  class LogProps extends React.Component {
    componentDidUpdate(prevProps) {
      console.log('old props:', prevProps);
      console.log('new props:', this.props);
    }

    render() {
      const {forwardedRef, ...rest} = this.props;
      // Assign the custom prop "forwardedRef" as a ref
      return <Component ref={forwardedRef} {...rest} />;    }
  }

  // Note the second param "ref" provided by React.forwardRef.
  // We can pass it along to LogProps as a regular prop, e.g. "forwardedRef"
  // And it can then be attached to the Component.
  return React.forwardRef((props, ref) => {    return <LogProps {...props} forwardedRef={ref} />;  });}

Displaying a custom name in DevTools

React.forwardRef accepts a render function. React DevTools uses this function to determine what to display for the ref forwarding component.

For example, the following component will appear as ”ForwardRef” in the DevTools:

const WrappedComponent = React.forwardRef((props, ref) => {
  return <LogProps {...props} forwardedRef={ref} />;
});

If you name the render function, DevTools will also include its name (e.g. ”ForwardRef(myFunction)”):

const WrappedComponent = React.forwardRef(
  function myFunction(props, ref) {
    return <LogProps {...props} forwardedRef={ref} />;
  }
);

You can even set the function’s displayName property to include the component you’re wrapping:

function logProps(Component) {
  class LogProps extends React.Component {
    // ...
  }

  function forwardRef(props, ref) {
    return <LogProps {...props} forwardedRef={ref} />;
  }

  // Give this component a more helpful display name in DevTools.
  // e.g. "ForwardRef(logProps(MyComponent))"
  const name = Component.displayName || Component.name;  forwardRef.displayName = `logProps(${name})`;
  return React.forwardRef(forwardRef);
}