The resize event is triggered when the window is resized. Use window.outerWidth and window.outerHeight event in JavaScript to get the size of windows when the browser is resized.
Example
You can try to run the following code to work with an onresize event in JavaScript.
<!DOCTYPE html>
<html>
<head>
<script>
function resizeFunction() {
var val = "Window Width=" + window.outerWidth + ", Window Height=" + window.outerHeight;
document.getElementById("test").innerHTML = val;
}
</script>
</head>
<body onresize="resizeFunction()">
<p>Resize browser window and check the window (browser window) height and width again.</p>
<p id = "test"> </p>
</body>
</html>