JSFiddle - React, Tailwind, and code Playground

HTML

<div id="bar">
    
    <div id="child"></div>
    
</div>

CSS

#bar{
    width:200px;
    height:20px;
    background-color:black;
    position:relative;
}
#child{
    position:abosoute;
    top:0px;
    left:0px;
    background-color:red;
    height:20px;
}

JavaScript

var d = document.getElementById('child');

function run(div,i){
i += 1;
div.style.width = i+'px';
 if(i > 200) i = 200;
div._timer = setTimeout(function () {
run(div,i)
 },100);

}

run (d,0);