Twenty Thirteen: improve jQuery code: remove deprecated functions, namespace events, and more

[obenland]

1. The syntax $(document).on("ready", handler) is deprecated as of jQuery 1.8.

It behaves similarly to the ready method but if the ready event has already fired and you try to .on("ready") the bound handler will not be executed. See: ​http://api.jquery.com/ready/

2. We should namespace events: ​http://docs.jquery.com/Namespaced_Events

3. The scroll event should be throttled for performance.

[lancewillett]

I'm going to leave this 'til after beta, we can do some other general refactoring here.

[nacin]

In 23891:

Don't use jQuery.on('ready'). props obenland. see #23875.

[lancewillett]

.1 patch does the following:

• Moves away from namespaced function names, just make them same scope as other variables
• Add event namespacing
• Add debounce function and use it to throttle scroll events
• Code comment improvements

[lancewillett]

In 24004:

Twenty Thirteen: improvements to functions.js to add namespacing to events and simplify repeatable functions. See #23875.

[lancewillett]

.3 builds on .2 from obenland to introduce a short delay so we don't trigger an avalanche of function calls with the scroll handler.

Thoughts on the UX? The navbar will hide and show with a tiny delay instead of being instant.

[lancewillett]

In 24005:

Twenty Thirteen: further performance for functions.js scroll event callback, props obenland. See #23875.

[lancewillett]

Further improvements to the scroll event now pending a decision: we discussed removing the fixed navbar completely today, in IRC #wordpress-dev, ​see log.

[lancewillett]

@mfields brought to my attention a possible XSS vulnerability at ​https://wpcom-themes.trac.automattic.com/browser/twentythirteen/js/functions.js#L102

Where we don't check that the hash input is a valid element in the DOM.

See .4 diff for his suggested patch.

This approach is closer to the original code at ​http://www.nczonline.net/blog/2013/01/15/fixing-skip-to-content-links/ and also closes a possible XSS vulnerability in jQuery Migrate, see ​https://github.com/jquery/jquery-migrate/issues/36.

[lancewillett]

In 24070:

Twenty Thirteen: update JavaScript-based accessibility function hooked to hashchange event to verify user input correctly. Props mfields for the original patch.

Also add textarea to list of elements. See #23875.

[lancewillett]

Closing now that #24184 negates the need to throttle the scroll event (which will be removed).