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To check if an element has focus in React:

1. Set the ref attribute on the element.
2. After the element is rendered, check if the element is the active element in the document.
3. If yes, the element is focused.

import {useEffect, useRef} from 'react';

export default function App() {
  const ref = useRef(null);

  // 👇️ check if an element is focused on mount
  useEffect(() => {
    if (document.activeElement === ref.current) {
      console.log('element has focus');
    } else {
      console.log('element does NOT have focus');
    }
  }, []);

  return (
    <div>
      <input ref={ref} autoFocus type="text" id="message" name="message" />
    </div>
  );
}

The code example shows how to check whether an element has focus.

const ref = useRef(null);

The useRef() hook can be passed an initial value as an argument. The hook returns a mutable ref object whose .current property is initialized to the passed argument.

请注意, we have to access the current property of the ref object in order to access the input element on which we set the ref attribute.

useEffect(() => {
  if (document.activeElement === ref.current) {
    console.log('element has focus');
  } else {
    console.log('element does NOT have focus');
  }
}, []);

When we pass a ref prop to an element, for example <input ref={myRef} />, React sets the .current property of the ref object to the corresponding DOM node.

We pass an empty dependenciesarray to useEffectthe hook, so it will only run when the component mounts.

We use useEffectthe hook because we want to make sure that the ref has been set on the element and that the element has been rendered.

document.activeElementProperty returns the element that currently has focus.

If there is no focused element, the document.activeElement property will return the body element in most browsers, but it may also return null, depending on the browser implementation.

We simply check document.activeElementif is equal to ref.currentand if the expression returns true, then the element has focus.

Use onFocus and onBlur to check if an element is focused

This is a three-step process:

1. onFocusSet the and attributes on the element onBlur.
2. Each onFocustime the event runs, isFocusedset the state variable to true .
3. Each onBlurtime the event runs, isFocusedset the state variable to false .

import {useEffect, useRef, useState} from 'react';

export default function App() {
  const [isFocused, setIsFocused] = useState(false);
  const ref = useRef(null);

  useEffect(() => {
    console.log('isFocused: ', isFocused);
  }, [isFocused]);

  return (
    <div>
      <input
        ref={ref}
        type="text"
        id="message"
        name="message"
        onFocus={() => setIsFocused(true)}
        onBlur={() => setIsFocused(false)}
      />

      <h2>jiyik.com</h2>
    </div>
  );
}

onFocusWe set the and properties on the element onBlurto check if it has focus.

Every time the element gets focus, onFocusthe event runs and we isFocusedset the state variable to true .

When the element loses focus, onBlurthe event runs and we set the state variable to false .

If we need to track isFocusedchanges to state variables, we can use useEffectthe hook.