JS Dynamic load JS file implementation method

<script language= "Web Effects" type= "Text/javascript"
<!--
Function Jsloader () {
 this.load= function (URL) {
  //gets all <scrcipt> tags
  var ss=document.getelementsbytagname (" Script "); The
  //determines whether the specified file already contains, if it is already included, triggers the Onsuccess event and returns
  for (i=0;i<ss.length;i++) {
    if (ss[i].src && ss[i].src.indexof (URL)!=-1) {
    this.onsuccess ();
    return;
   }
  }
  //creates a script node and sets its properties to be an external JavaScript file
  s=document.createelement ("script");
  s.type= "Text/javascript";
  s.src=url;
  //Gets the head node and inserts <script> into it
  var head=document.getelementsbytagname ("Head") [ 0];
  head.appendchild (s);
  //Gets the reference to the object itself
  var self=this;

  //for IE browsers, use the ReadyStateChange event to determine whether to load successfully
  //for other browsers, use the OnLoad event to determine whether the load was successful
   s.onload=s.onreadystatechange=function () {
   //this pointer in this function refers to an S-node object, not a Jsloader instance,
   //so you have to use self to invoke the Onsuccess event, the same below.
   if (this.readystate && this.readystate== "Loading") return;
   self.onsuccess ();
  }
  s.onerror=function () {
   //If an error occurs, delete the inserted node and trigger the failed event
    Head.removechild (s);
   self.onfailure ();
  }
 };
 //Define Load Success Events
 this.onsuccess=function () {};
 //define load failed events
 this.onfailure= function () {};
}
//Create Object
var jl=new jsloader ();
//define load successful handler
Jl.onsuccess=function () {
 sayhello ();
}
//Define Load Failure handler
Jl.onfailure=function () {
 alert ("File load failed! ");
}
//Start loading
jl.load ("Hello.js");

//-->
</script>