JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mydiv"></div>

CSS

#mydiv {
    background: #FEB100;
    width: 200px;
    height: 100px;
    margin-left: 50px;
}

JavaScript

window.onload = function() {
	// Select a div with the id 'mydiv'
    var mydiv = document.getElementById('mydiv');
    
    // Get all offsets
    var offset = mydiv.getBoundingClientRect();
    
    // Offset of the div from the right side of the viewport
    var offsetRight = document.documentElement.clientWidth - offset.right;
    
    // Offset of the div from the left side of the viewport
    var offsetLeft = offset.left;

    alert("Right Offset: " + offsetRight);
    alert("Left Offset: " + offsetLeft);
}