JSFiddle - React, Tailwind, and code Playground

HTML

<body style="width:1000px;height:1000px;">
    <div id="d" style="display:inline-block;">
        <svg id="s" xmlns="http://www.w3.org/2000/svg" version="1.1" width="200px" height="200px">
          <rect width="200px" height="200px" style="fill:rgb(0,0,255);"/>
        </svg>
    </div>
</body>

CSS

* 
{
    margin: 0;
    padding: 0;
}

JavaScript

var div = document.getElementById('d');
var rect = div.getBoundingClientRect();

alert(rect.width);
alert(rect.height);

var svg = document.getElementById('s');
var rect = svg.getBBox();

alert(rect.width);
alert(rect.height);