loadScript

function loadScript(url,callback){
	var script = document.createElement("script");
	script.type = "text/javascript";
	
	if(script.readyState){
		script.onreadystatechange = function(){
			if(script.readyState =='loaded' || script.readyState == 'complete'){
				script.onreadystatechange = null;
				callback();
			}
		}
	}
	else{
		script.onload = function(){
			callback();
		}
	}
script.src = url;
document.getElementsByTagName("head")[0].appendChild(script);	
}

loadScript('file1.js',function(){
	loadScript('file2.js',function(){
		alert("file file2 loaded!")
	});
})