JSFiddle - React, Tailwind, and code Playground

HTML

<div id="myDiv" class="container">
</div>
<input type="button" value="Get Width of myDiv" id="getWidth"/>
    <input type="button" value="Set Width of myDiv to 200px" id="setWidth"/>

CSS

div.container {
    width: 300px;
    height: 400px;
    border: solid 1px black;
    overflow: hidden;
    background:  #efefef;
}

JavaScript

$('#getWidth').on('click', function(){
    alert($('#myDiv').width());  
});
$('#setWidth').on('click', function(){
    $('#myDiv').css("width","200px");
    alert("New Width : " + $('#myDiv').width());  
});