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

loadScript("file1.js", function(){
alert("File is loaded!");
});