JSFiddle - React, Tailwind, and code Playground
HTML
<div id="container" class="main"></div>
CSS
.main {
border: 1px solid lightblue;
width: 400px;
height: 100px;
padding: 5px;
}
JavaScript
$(document).ready(function() {
var width = $("#container").outerWidth();
alert(width);
});