<h1 id="size">window size</h1>
body{width: 100%; border: 10px solid red; margin: 0 auto;}
h1{text-align: center;}
var size = document.getElementById("size");
window.onresize = function(event){
var innerWidth = window.innerWidth;
size.textContent = innerWidth;
}
This Pen doesn't use any external CSS resources.
This Pen doesn't use any external JavaScript resources.