Defer loading javascript

defer.js

// ref: https://varvy.com/pagespeed/defer-loading-javascript.html

function downloadJSAtOnload() {
	
	const scripts = ['defer.js', 'defer2.js', 'defer3.js'];
	
	scripts.forEach(function(script){
		const element = document.createElement("script");
		element.src = script;
		document.body.appendChild(element);
	})
}

downloadJSAtOnload();

if (window.addEventListener){
	window.addEventListener("load", downloadJSAtOnload, false);
}

else if (window.attachEvent){
	window.attachEvent("onload", downloadJSAtOnload);
}

else {
	window.onload = downloadJSAtOnload;
}