how to check if specific class exists in javascript code example

Example 1: javascript check if element has class

if(document.getElementById("myElmentID").classList.contains("hidden")){
// I have the 'hidden' class
}

Example 2: js check for class in classList

element.classList.contains(className);

Example 3: check if a class exists javascript

const element = document.querySelector("#box");

element.classList.contains("active");