UseImperativeHandle Hook Easily Explained

What does the useImperativeHandle hook do? In the simplest terms, it allows you to control what is returned by a ref prop, specifically the ref handle. The handle is usually a DOM node, but by using this hook, the handler would instead be replaced by an object with methods.

In what situations would you use this? As far as I can tell, its main use case is to restrict access to the DOM. Imagine you are the creator of a form library. You would want to maintain strong control over the form elements and prevent users from unnecessarily manipulating the DOM. It should be noted that this hook is quite advanced in its use case and is therefore rarely used.

Common Example

Take the example of an input field for which you solely expose the ability to focus it. The 1^st argument of useImperativeHandle accepts the ref passed in as a prop from the parent component. The 2^nd argument accepts the new handler, i.e. a JavaScript object with custom methods. Lastly, the 3^rd argument takes in an array of dependencies, the same as many other React hooks.

const MyInput = React.forwardRef((props, ref) => {
  const realInputRef = React.useRef(null)

  React.useImperativeHandle(
    ref, // Target the ref passed in by the parent.
    () => ({
      // Only expose focus and nothing else.
      focus() {
        realInputRef.current.focus()
      },
    }),
    [] // Add any dependencies the hook relies on.
  )

  return <input {...props} ref={realInputRef} />
})

function Form() {
  const inputRef = React.useRef(null)

  function handleClick() {
    // `current` contains a JavaScript object, not a DOM node.
    inputRef.current.focus()
  }

  return (
    <>
      <MyInput ref={inputRef} /> {/* Remove the ref and see what happens! */}
      <button onClick={handleClick}>Focus the input</button>
    </>
  )
}

render(<Form />)