JAVASCRIPT

onclick add class javascript

<div class="cl1">test</div>
<button onlick="change()">change</button>

// javaScript part 
let elemnt = document.getElementsByClassName("cl1")
function change(){
// "add" is gonna add classe one time if you click again class is not gonna remove if you want to change class and remove it with 2 click use toggle
// add
  elemnt.classList.add("cl2")
// toggle
  elemnt.classList.toggle("cl2")
}

add class on javascript onclick function

document.addEventListener('click', function handleClick(event) {
  console.log('user clicked: ', event.target);

  event.target.classList.add('bg-yellow');
});