Open Radar

 
Summary:
When setting the JS onbeforeunload event, the dialogue is only shown until the user chooses to navigate away.
On subsequent pages on the same site, the onbeforeunload function is called, but the dialogue is no longer shown.

Steps to Reproduce:
1. Open a new tab and navigate to any page (e.g. apple.com)
2. Open the JS console and paste the following:
    window.onbeforeunload = function() {return true;};
3. Click on the page
4. Hit Refresh
5. *Observe the warning is shown*
6. Click to stay
7. Hit Refresh again
8. *Observe the warning is shown*
9. Click to leave (the page will refresh)
10. Paste exactly the same code in the JS console again
11. Hit refresh
12. *Observe that the warning is not shown* :(

Expected Results:
The dialogue should once again confirm whether you wish to leave

Actual Results:
The dialogue does not confirm

Version:
OS X 10.11.6 (15G1004); Safari: Version 9.1.3 (11601.7.8)

OSX: 10.12 (16A323); Safari: Version 10.0 (12602.1.50.0.10)

Notes:
If the user navigates to a different site (e.g. initially on apple.com, then moves to icloud.com) then the dialogue is shown for one page on that site too. Upon navigating back to the first site, it works there again for one time.

Having the JS return nothing:
    window.onbeforeunload = function() {return;}
instead of clicking on the Leave button means that subsequent pages work, but this doesn't really solve the issues with the typical usage of this feature - e.g. to confirm whether a user wants to move away from a page after making changes to a form.

See https://tracker.moodle.org/browse/MDL-56465 for our internal issue.

Configuration:
MacBook Air 11" Mid 2013 
MacBook Pro 13" Mid 2013

Attachments: