[wp-trac] [WordPress Trac] #37110: Update to jQuery 3.*

[WordPress Trac]

#37110: Update to jQuery 3.*
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 Reporter:  jorbin                               |       Owner:  (none)
     Type:  task (blessed)                       |      Status:  reopened
 Priority:  normal                               |   Milestone:  5.5
Component:  External Libraries                   |     Version:
 Severity:  critical                             |  Resolution:
 Keywords:  early has-patch needs-testing        |     Focuses:  javascript
  needs-screenshots has-dev-note commit          |
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Comment (by desrosj):

 I just posted a lengthy summary of some more research I did with @Clorith
 in #core. I am posting here for anyone that is not in Slack or following
 #core.

 > I have been doing some experimenting and testing on different plugins
 that were flagged in the
 [https://wpdirectory.net/search/01EF25266C24AHENKPW7RYWYRK list of ~11k as
 potentially breaking] when jQuery Migrate is not loaded. As I started to
 dig in, though, there were a ton of false positives.
 >
 > The original plugin search was flagging 9 different functions/patterns
 that may cause issues. This paints a complete picture of everything that
 could break when jQuery gets upgraded to 3.x. But that's not what we need
 to be looking at right now. We need to be looking at what plugins or
 themes could break if jQuery Migrate is not loaded and jQuery 1.12.x is
 loaded (the version currently shipping with WordPress).
 >
 > That whittles down the list of functions/patterns to 6. These will cause
 deprecated notices in the console, but they will not break sites until
 jQuery is upgraded to 3.x. This only
 [https://wpdirectory.net/search/01EF2Y84Y3SXK8KZH6SMGJ1XFA decreases the
 number of results by a few hundred]. However, there are still a very large
 number of false positives.
 >
 > There are two uses for load, a way to inject content from a remote
 source is removed in 1.9, but the same function used as a shortcut for
 .on('load') is not removed until 3.x. The latter needs to be weeded out of
 the results. Also, Colorbox (a common lightbox script back in the day) is
 packaged with many plugins and themes. But this library contains a
 compatibility check, only using load  incorrectly if jQuery <1.9 is being
 loaded.
 >
 > I was just working with @clorith, and he was able to massage the regex
 search to account for these false positives. This results in
 [https://wpdirectory.net/search/01EF31985CZ46Q1QTEHPSR0JZB ~2400 plugins
 with the potential to break] when jQuery Migrate is disabled upon
 upgrading to 5.5.
 >
 > There are still some Colorbox false positives for plugins and themes
 that have slightly older versions of the library, and some compatibility
 checks (I spotted 3-4 on a quick scan of the first page of results), but
 this is significantly less than the original list that we have been using
 in the discussions so far, and there are NO plugins with over 1m active
 installs on the list (the only one there is a false positive).
 >
 > For themes, these changes to the search bring the results from
 [https://wpdirectory.net/search/01EF034N6A2CCQ0WQ08P8Z3BXW ~2600 themes]
 to [https://wpdirectory.net/search/01EF30MTKX3AKK868EYJRBJHFC ~250
 themes], with only 5 having more than 10k active installs.
 >
 > With this updated information in mind, I think that we are on the right
 path for proceeding as is (disabling jQuery Migrate in 5.5). We should
 still make it easy for plugin/theme developers to re-add Migrate if they
 need more time. The plugin that is being built should still be released
 and plugin devs/site owners can still install this if they need more time
 updating their code (and don't want to re-enqueue it themselves) or
 experience any issues upon upgrading to 5.5.
 >
 > But I wanted to summarize this information here for further discussion,
 just in case @clorith and I are misinterpreting something.

 With all this in mind, I think [attachment:"37110-add-dependency.3.diff"]
 is a low risk way to add a way for devs to re-enable jQuery Migrate, and
 can be complicated with the jQuery Tester plugin that @Clorith and @azaozz
 are working on (for non-devs, and those that don't want to add a code
 snippet). [attachment:"37110-add-dependency.3.diff"] will not break
 anything when we remove it along with the jQuery 3.x and jQuery Migrate
 update in step 2.

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Ticket URL: <https://core.trac.wordpress.org/ticket/37110#comment:176>
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