//getting the viewport dimensions
var width= Math.max(document.documentElement.clientWidth, window.innerWidth || 0);
var height = Math.max(document.documentElement.clientHeight, window.innerHeight || 0);var isInViewport = function (elem) {
var bounding = elem.getBoundingClientRect();
return (
bounding.top >= 0 &&
bounding.left >= 0 &&
bounding.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
bounding.right <= (window.innerWidth || document.documentElement.clientWidth)
);
};
<meta name="viewport" content="width=device-width, initial-scale=1.0">