SCORM, closing windows, LMSFinish and synchronous XHR dismissals

Symptom

Upon closing a SCORM course, the LMS doesn't do [something expected] when using a modern browser.

SCORM overview

The LMS makes a series of named functions (an API called SCORM) available in JavaScript which the content JavaScript interacts with. The content does not directly communicate with the LMS except through this SCORM API. The back end of the SCORM API, implemented by the LMS, communicates with the LMS on the course's behalf using http requests.

Problem summary

When the course is closed, the course calls the LMS's SCORM function LMSFinish. In this case, the LMSFinish function uses a synchronous, or blocking, http request. Modern browsers prevent blocking https requests in order to stop browser windows from hanging whilst a request is being performed. Instead, asynchronous or non-blocking http requests are performed so that the browser window stays performant whilst in use.

Problem use-case

Old method

1. [the user clicks the window close button]
2. Window triggers beforeunload event
   a) LMSFinish starts a blocking request, causing the browser to hang
   b) LMSFinish finishes a blocking request
3. Window triggers unload event
4. Browser closes

New problem

1. [the user clicks the window close button]
2. Window triggers beforeunload event
   a) LMSFinish starts a non-blocking request (which never finishes)
3. Window triggers unload event
4. Browser closes

Bad solutions

Call LMSFinish and wait for it to complete before closing the window

We could change the way Adapt works to do an asynchronous (non-blocking) http request first, before any call to window.close, but window.close is only one way of closing the window. We aren't able trap or prevent or stop or delay other methods of closing a window in order to allow a non-blocking call to LMSFinish first.

For example, when a user clicks the window's close button, the JavaScript function window.close is never called, but the window triggers its unload events - which can't be stopped - Adapt calls LMSFinish from a window unload event handler, and then the browser then closes. LMSFinish in modern browsers (remember that LMSFinish is implemented by the LMS) is now not allowed to make a blocking http request, so if it does, the browser closes before the course's finishing http request is complete.

Semi solutions

You could add an additional close button to your course, which calls LMSFinish when clicked, (see adapt-close). This won't stop users clicking the window close button and losing their stuff as this isn't an LMS fix for the LMSFinish function but it may buy you time until you can fix your LMS.