Distinguish onbeforeunload for File Download vs Page Change

I have an onbeforeunload event that's supposed to get triggered any time a user goes to a new page. It works well enough, but I've found that it also gets triggered in Chrome any time a user downloads a file from the page they're on.

I'd like to be able to tell if the event is getting fired because it's being triggered by a file download. What's the best way to do that?

EDIT: As a clarification, I don't own the site that I'm listening to onbeforeunload on. The event is listened to by a Javascript snippet that's being installed on 3rd party sites.

Solution

A javascript work around

That's the only "clean" work around I could think of & it seems to work just fine.

Some more code in your question showing how you actually use the "onbeforeunload" would be great.

But I will assume you are using something like the code below for the cursor "loading..." animation.

/* Loading Progress Cursor
 * 
 * Tested on:    IE8, IE11, Chrome 37, & Firefox 31
 * 
 * [1] the wildcard selector is not performant but unavoidable in this case
 */ 
.cursor-loading-progress,
.cursor-loading-progress * { /* [1] */
  cursor: progress !important;
}

The solution

1st step:

/* hooking the relevant form button
 * on submit we simply add a 'data-showprogresscursor' with value 'no' to the html tag
 */
$(".js-btn-download").on('submit', function(event) {
    $('html').data('showprogresscursor', 'no' );
});

2nd step:

/* [1] when page is about to be unloaded
 * [4] here we have a mechanism that allows to disable this "cursor loading..." animation on demand, this is to cover corner cases (ie. data download triggers 'beforeunload')
 * [4a] default to 'yes' if attribute not present, not using true because of jQuery's .data() auto casting
 * [4b] reset to default value ('yes'), so default behavior restarted from then on
 */
var pageUnloadOrAjaxRequestInProgress = function() {
    /* [4] */
    var showprogresscursor = $('html').data('showprogresscursor') || 'yes';  /* [4a] */
    if( showprogresscursor === 'yes' ){
        $('html').addClass('cursor-loading-progress');
    }
    else {
        $('html').data('showprogresscursor', 'yes' );  /* [4b] */
    }
}

$( window ).on('beforeunload', function() {    /* [1] */
    pageUnloadOrAjaxRequestInProgress();
});

Note that I use $('html').addClass('cursor-loading-progress'); as this is the expected CSS in my example but you can just do anything you like at this point.

Another couple of work arounds could be:

To open the file download page in a new tab
To trigger a page refresh once the file download is done