Load a script with a call back when it is done loading. For scripts that depend on each other

js script loader

    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 = url;
        document.getElementsByTagName("head")[0].appendChild(script);
    }