How can assign multiple css classes to an html element through javascript without using any libraries?
You can add and remove multiple classes in same way with different in-built methods:
const myElem = document.getElementById('element-id');
//add multiple classes
myElem.classList.add('class-one', 'class-two', 'class-three');
//remove multiple classes
myElem.classList.remove('class-one', 'class-two', 'class-three');