Cross Browser solution to show progress bar while loading javascript files

Question

I was looking for a way that I can show a (gmail-like) progress bar when the page is loading js file. reading this post I wrote a code that helped me to show the progress bar in mozilla FireFox as this other post states!

  var oReq = new XMLHttpRequest();

  oReq.addEventListener("progress", updateProgress, false);
  oReq.addEventListener("load", transferComplete, false);
  oReq.addEventListener("error", transferFailed, false);
  oReq.addEventListener("abort", transferCanceled, false);

  oReq.open();

  // ...

  // progress on transfers from the server to the client (downloads)
  function updateProgress (oEvent) {
    if (oEvent.lengthComputable) {
      var percentComplete = oEvent.loaded / oEvent.total;
      // ...
    } else {
      // Unable to compute progress information since the total size is unknown
    }
  }

  function transferComplete(evt) {
    alert("The transfer is complete.");
  }

  function transferFailed(evt) {
    alert("An error occurred while transferring the file.");
  }

  function transferCanceled(evt) {
    alert("The transfer has been canceled by the user.");
  }

I would like to write a cross browsers solution How to do it?