Hey all,

TL;DR: jQuery will soon be upgraded from v1.8.3 to v1.11.x (the latest). This
major release removes deprecated functionality. Please migrate away from this
deprecated functionality as soon as possible.

It's been a long time coming but we're now finally upgrading the jQuery package
that ships with MediaWiki.

We used to regularly upgrade jQuery in the past, but got stuck at v1.8 a couple
of years ago due to lack of time and concern about disruption. Because of this,
many developers have needed to work around bugs that were already fixed in later
versions of jQuery. Thankfully, jQuery v1.9 (and its v2 counterpart) has been
the first release in jQuery history that needed an upgrade guide[1][2]. It's a
major release that cleans up deprecated and dubious functionality.

Migration of existing code in extensions, gadgets, and user & site scripts
should be trivial (swapping one method for another, maybe with a slight change
to the parameters passed). This is all documented in the upgrade guide[1][2].
The upgrade guide may look scary (as it lists many of your favourite methods),
but they are mostly just addressing edge cases.

== Call to action ==

This is a call for you, to:

1) Get familiar with http://jquery.com/upgrade-guide/1.9/.

2) Start migrating your code.

jQuery v1.9 is about removing deprecated functionality. The new functionality is
already present in jQuery 1.8 or, in some cases, earlier.

3) Look out for deprecation warnings.

Once instrumentation has begun, using "?debug=true" will log jQuery deprecation
warnings to the console. Look for ones marked "JQMIGRATE" [7]. You might also
find deprecation notices from mediawiki.js, for more about those see the mail
from last October [8].

== Plan ==

1) Instrumentation and logging

The first phase is to instrument jQuery to work out all the areas which will
need work. I have started work on loading jQuery Migrate alongside the current
version of jQuery. I expect that to land in master this week [6], and roll out 
Wikimedia wikis the week after. This will enable you to detect usage of most
deprecated functionality through your browser console. Don't forget the upgrade
guide[1], as Migrate cannot detect everything.

2) Upgrade and Migrate

After this, the actual upgrade will take place, whilst Migrate stays. This
should not break anything since Migrate covers almost all functionality that
will be removed. The instrumentation and logging will remain during this phase;
the only effective change at this point is whatever jQuery didn't think was
worth covering in Migrate or were just one of many bug fixes.

3) Finalise upgrade

Finally, we will remove the migration plugin (both the Migrate compatibility
layer and its instrumentation). This will bring us to a clean version of latest
jQuery v1.x without compatibility hacks.

A rough timeline:

* 12 May 2014 (1.24wmf4 [9]): Phase 1 – Instrumentation and logging starts. This
  will run for 4 weeks (until June 9).

* 19 May 2014 (1.24wmf5): Phase 2 – "Upgrade and Migrate". This will run for 3
  weeks (upto June 9). The instrumentation continues during this period.

* 1 June 2014 (1.24wmf7) Finalise upgrade.

== FAQ ==

Q: The upgrade guide is for jQuery v1.9, what about jQuery v1.10 and v1.11?

A: Those are regular updates that only fix bugs and/or introduce non-breaking
enhancements. Like jQuery v1.7 and v1.8, we can upgrade to those without any
hassle. We'll be fast-forwarding straight from v1.8 to v1.11.

Q: What about the jQuery Migrate plugin?

A: jQuery developed a plugin that adds back some of the removed features (not
all, consult the upgrade guide[2] for details). It also logs usage of these to
the console.

Q: When will the upgrade happen?

A: In the next few weeks, once we are happy that the impact is reasonably low.
An update will be sent to wikitech-l just before this is done as a final 
This will be well before the MediaWiki 1.24 branch point for extension authors
looking to maintain compatibility.

Q: When are we moving to jQuery v2.x?

A: We are not currently planing to do this. Despite the name, jQuery v2.x
doesn't contain any new features compared to jQuery v1 [3]. The main difference
is in the reduced support for different browsers and environments; most
noticeably, jQuery 2.x drops support for Internet Explorer 8 and below, which
MediaWiki is still supporting for now, and is outside the scope of this work.
Both v1 and v2 continue to enjoy simultaneous releases for bug fixes and new
features. For example, jQuery released v1.11 and v2.1 together[4][5].

-- Krinkle

[1] http://blog.jquery.com/2013/01/15/jquery-1-9-final-jquery-2-0-beta-migrate-
[2] http://jquery.com/upgrade-guide/1.9/
[3] http://blog.jquery.com/2013/04/18/jquery-2-0-released/
[4] http://blog.jquery.com/2014/01/24/jquery-1-11-and-2-1-released/
[5] http://blog.jquery.com/2013/05/24/jquery-1-10-0-and-2-0-1-released/
[6] https://gerrit.wikimedia.org/r/131494
[7] https://github.com/jquery/jquery-migrate/blob/master/warnings.md
[8] http://www.mail-archive.com/wikitech-l@lists.wikimedia.org/msg72198.html
[9] https://www.mediawiki.org/wiki/MediaWiki_1.24/Roadmap

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