Check If an Element contains a Class

To check if an element contains a class, you use the contains() method of the classList property of the element:

element.classList.contains(className);

Suppose you have the following <div> element:

<div class="secondary info">Item</div>

To check if the <div> element contains the secondary class, you use the following code:

const div = document.querySelector('.info');
div.classList.contains('secondary'); // true

The following returns false because the <div> element doesn’t have the error class:

const div = document.querySelector('.info');
div.classList.contains('error'); // false

Source