How to change element's class in JavaScript?

9awohc2.js

// Change the class altogether?
document.getElementById("MyElement").className = "MyClass";

// Add to the class?
document.getElementById("MyElement").className += "MyClass";

// Add or Remove a new class?
document.getElementById("MyElement").classList.add('MyClass');
document.getElementById("MyElement").classList.remove('MyClass');

// Check if an element has a class?
if ( document.getElementById("MyElement").classList.contains('MyClass') )

// Toggle a class on an element?
document.getElementById("MyElement").classList.toggle('MyClass');