How jQuery.getScript should work!

getScript.js

function getScript (src, callback) {
	var scripts = document.getElementsByTagName('script');
	var script = document.createElement("script");
	var once = true;
	script.async = "async";
	script.type = "text/javascript";
	script.src = src;
	script.onload = script.onreadystatechange = function () {
		if (once && (!script.readyState || /loaded|complete/.test(script.readyState))) {
			once = false;
			callback();
		}
	};
	scripts[0].parentNode.insertBefore(script, scripts[0]);
}