Step 55 – Delaying Loading of the SCO

In the past, I’ve had some intermittent problems with a SCO loading but showing a Javascript error. Although I couldn’t pin it down conclusively, it seemed to result from an incomplete download of some kind. Since forcing a reload with CTRL-R or CTRL-F5 usually solved the problem, I just put it down to something that I had to live with because SCORM forces us to use Javascript which can be very fickle.

But, recently, reader ‘deighvan’ reported a similar problem and, even better, came up with a simple solution. So I’ve incorporated a slightly modified form of this solution in a new version of the rte.php file.

Here it is:



VS SCORM 1.2 RTE - rte.php
Rev XXXXXXXXXXX was 2009-11-30-01
Copyright (C) 2010, Addison Robson LLC

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, 
Boston, MA  02110-1301, USA.


// read SCOInstanceID from the GET parameters
$SCOInstanceID = $_GET['SCOInstanceID'] * 1;

  <title>VS SCORM</title>
  <script language="javascript">

    var started = false;

    function loadSCO() {
      if (! started) {
        SCO.location.href = '... location of the SCO ...';
      started = true;

    function unloadSCO() {

<frameset frameborder="0" framespacing="0" border="0" rows="50,*" cols="*" onbeforeunload="unloadSCO();" onunload="unloadSCO();">
  <frame src="api.php?SCOInstanceID=<?php print $SCOInstanceID; ?>" name="API" id="API" noresize onload="loadSCO();">
  <frame src="blank.html" name="SCO" id="SCO">

And here are the changes … line-by-line:

  • Line 35 – I define a Javascript variable called ‘started’ and set it to false. This will be used to prevent the SCO being started twice.
  • Lines 37 to 42 – I’ve added a new Javascript function that, when called, will load the SCO into the ‘SCO’ frame.
  • Line 51 – I’ve added an ‘onload’ action. When the api.php code has completely loaded into the frame, this will call loadSCO() which will start the SCO.
  • Line 52 – When the frameset starts, I’m going to load a blank document into the ‘SCO’ frame. Why not just start with an empty frame (i.e. src=”)? Because, if I’m going to be running over an SSL connection, Internet Explorer considers an empty frame to be an insecure document and will pop up a warning message that’s annoying, and also worrying to many students.

So I try it out, and it seems to work much more smoothly than before. Once again, thanks to reader ‘deighvan’ for the suggestion.

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4 Responses to Step 55 – Delaying Loading of the SCO

  1. Steve Addison says:

    Even better, replace ‘blank.html’ with an HTML file that displays a “Loading … Please Wait” message!

  2. deighvan says:

    Good call! Doing that now…

  3. Good stuff Steve, just stumbled across your site. I’ve been working on LMSs for almost 10 years, and SCORM quirks certainly trip us up a lot. A nice project you have here – any progress since the summer?


  4. Steve Addison says:

    Just starting up again – moving on to errors codes and logging, and a test harness to make it easier to diagnose SCO/LMS communication problems. A new post should be out later today to start things rolling.

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