Use native focus events insted of jQuery focus events

[jwmerrill]

jQuery 3.x has introduced a bunch of different focus bugs in the process of attempting to migrate to using native focus events in more cases, some of which remain unfixed in the latest version (3.6.0).

Examples:

• jQuery v3.6.0 breaks Bootstrap's test suite in IE jquery/jquery#4859
• In jQuery 3.4.0+ in IE a focus-blur-focus sequence doesn't leave the element focused jquery/jquery#4856
• You cannot programmatically focus an element after you have attempted to focus it while it was hidden (display:none) jquery/jquery#4950
• You cannot programmatically focus an element after removing its focus handler jquery/jquery#4867

Some unknown bug in this general class can make it so that Mathquill public api focus calls stop working because using jQuery to programatically trigger focus breaks.

Work around this by switching to calling the native DOM .focus() method instead of the jQuery .focus() method.

[sclower]

Thanks for this update. I have confirmed it fixes the focus problems with JQuery 3.6.0.

[jwmerrill]

I got a little anxious (partly based on a StackOverflow answer) that the native .focus() method might cause different events to fire, either on the element that's being focused or on its parents, and either native and/or jquery events.

I set up a JSBin to test this (using the latest stable jQuery version: 3.6.0), and as far as I could determine, this is not the case.

Native programmatic focus: https://jsbin.com/cimidid/5
jQuery programmatic focus: https://jsbin.com/cimidid/7
Manual focus: https://jsbin.com/cimidid/8

I tested these in Firefox 95, Chrome 96, and Safari 15.0 on macOS 11.6, and all of them produce the same events and order:

jQuery focusin fired on input
jQuery focusin fired on container
native focus fired on input
jQuery focus fired on input
native focusin fired on input
native focusin fired on container

I also tested these in IE 11 on windows 10 (through browserstack), and all 3 of them produced the same events, in a consistent but different order from other browsers

native focusin fired on input
jQuery focusin fired on input
native focusin fired on container
jQuery focusin fired on container
native focus fired on input
jQuery focus fired on input

Based on these tests, I now think this change should actually be pretty safe to make, and should be unlikely to change typical observable behaviors of focusing mathquill elements (except to fix the intended bug).

[22aam]

all of the code looks good