addscript.js

function addScript(src){

    var script = document.createElement("script");
    script.src = src;
    script.onload = script.onreadystatechange = function(e){
        if(e && e.type == "load" || /loaded|complete/.test(script.readyState)){
            script.onload = script.onreadystatechange = null;
            console.log("foo.js added and ready");
        }
    }

    return (document.head || document.getElementsByTagName("head")[0]).appendChild(script);

}