Html code
<div class="container color-blue">
<h3>HI I am a container</h3>
</div>
js code
let div =document.getElementsByClassName('container')[0];
let a = div.classList;
// here is a is an object
// so I use array.from(a) to turn in into array
Array.from(a)[0] = "font";
"arrays are mutable and array can be chnaged" but it not replacing my container that is the first item of array with font