Remove CSS class from element with JavaScript (no jQuery) [duplicate]

Question

The right and standard way to do it is using classList. It is now widely supported in the latest version of most modern browsers:

ELEMENT.classList.remove("CLASS_NAME");

remove.onclick = () => {
  const el = document.querySelector('#el');
  el.classList.remove("red");
}

.red {
  background: red
}

<div id='el' class="red"> Test</div>
<button id='remove'>Remove Class</button>

Documentation: https://developer.mozilla.org/en/DOM/element.classList