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Check if an element has a class in React:

1. Sets the attribute on the element ref.
2. Use the method on the ref object classList.contains()to check if the class exists.
3. The method returns true if the element's class list contains the class .

import {useEffect, useRef} from 'react';

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

  // 👇️ check if element contains class on mount
  useEffect(() => {
    if (ref.current.classList.contains('my-class')) {
      console.log('Element contains class');
    } else {
      console.log('Element does NOT contain class');
    }
  }, []);

  // 👇️ check if element contains class on click
  const handleClick = event => {
    if (event.currentTarget.classList.contains('my-class')) {
      console.log('Element contains class');
    } else {
      console.log('Element does NOT contain class');
    }
  };

  return (
    <div>
      <div ref={ref} className="my-class" onClick={handleClick}>
        Hello world
      </div>
    </div>
  );
}

This code snippet shows how to check if an element contains a class when the component is mounted or when the element is clicked.

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

const ref = useRef(null);

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

// 👇️ 检查元素是否包含挂载类
useEffect(() => {
  if (ref.current.classList.contains('my-class')) {
    console.log('Element contains class');
  } else {
    console.log('Element does NOT contain class');
  }
}, []);

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

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

classList.containsThe method returns a Boolean value - true if the class is contained in the element's list of classes, false otherwise.

If we need to check if an element contains click class, set onClick attribute on the element.

Check if element has click class in React.js

Check if an element has a click class in React.js:

1. Sets the attribute on the element onClick.
2. event.targetUse the method on the object to classList.contains()check if an element contains this class.

import {useRef} from 'react';

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

  // 👇️ check if element contains class on click
  const handleClick = event => {
    if (event.currentTarget.classList.contains('my-class')) {
      console.log('Element contains class');
    } else {
      console.log('Element does NOT contain class');
    }
  };

  return (
    <div>
      <div
        ref={ref}
        className="my-class"
        onClick={handleClick}
        style={{backgroundColor: 'lime'}}
      >
        jiyik.com
      </div>
    </div>
  );
}

We set onClickthe property on the div element so that every time the element is clicked the handleClick function is called.

const handleClick = event => {
  if (event.currentTarget.classList.contains('my-class')) {
    console.log('Element contains class');
  } else {
    console.log('Element does NOT contain class');
  }
};

请注意, we used currentTargetthe property on the event because we want to access the element that the event listener is attached to.

The target property of the event gives us a reference to the element (possibly a descendant) that triggered the event.

In our handleClickmethod, we again use classList.contains()the method to check if the element contains the class.