function init() { var vidDefer = document.getElementsByTagName('iframe'); for (var i=0; i<vidDefer.length; i++) { if(vidDefer[i].getAttribute('data-src')) { vidDefer[i].setAttribute('src',vidDefer[i].getAttribute('data-src')); } } } window.onload = init;

defer iframe video

<style>
.resp-container {
    position: relative;
    overflow: hidden;
    padding-top: 56.25%;
}
.resp-iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: 0;
}
</style>
<div class="resp-container">
    <iframe class="resp-iframe" src="https://www.youtube.com/embed/dQw4w9WgXcQ" gesture="media"  allow="encrypted-media" allowfullscreen></iframe>
</div>
<script>
function init() {
	var vidDefer = document.getElementsByTagName('iframe');
	for (var i=0; i<vidDefer.length; i++) {
		if(vidDefer[i].getAttribute('data-src')) {
			vidDefer[i].setAttribute('src',vidDefer[i].getAttribute('data-src'));
		}
	}
}
window.onload = init;
</script>