How to Implement callback for file downloading?

Hello,

I wrote a script that downloads file from web using file URL. I have an ActiveXObject of following type.



var objHTTP = new ActiveXObject("MSXML2.XMLHTTP");  

objHTTP.open("GET", strFileURL, false);



It works perfect for small size file says, file size less than 100MB.  But when I try to download file with size greater than 100MB my script hanged. Then I tried,    



objHTTP.open("GET", strFileURL, true);



but in this case we have to implement a callback function. I don't know how to implement callback and then use it. Can somebody help me. I am using TestComplete 7. Script that I wrote;




  var objHTTP = new ActiveXObject("MSXML2.XMLHTTP");

  objHTTP.open("GET", strFileURL, true);

  objHTTP.onreadystatechange = Callback;

  objHTTP.send(); 

  while((objHTTP.readyState != 4) && (objHTTP.readyState != 'complete')) 

  {  

    Delay(100);

  } 

  if(200 != objHTTP.Status) 

  { 

    Log.Error("The " + strFileURL + " file was not found." + " The returned status is " + objHTTP.Status);

    return; 

  } 


I don't know how to implement Callback function. Can somebody provide me implementation?

Thanks