Twenty Twelve: Replace frontend jQuery usage with Interactivity API

[flixos90]

Using jQuery for a few simple JS interactions in WordPress themes is a common performance problem, which is in most cases relatively straightforward to address: Vanilla JavaScript has for the better part of a decade included enough APIs that work across all popular browsers so that the remaining benefits of jQuery are around a few utility functions, that could be re-implemented in a few lines of code. Using jQuery for such simple use-cases results in around 80% more JS code being loaded in the frontend.

This ticket focuses on removing jQuery as a frontend dependency for Twenty Twelve - specifically the frontend, as for example in the Customizer jQuery is loaded anyway (and performance is a bit less of a concern there).

• Replace jQuery usage in Twenty Twelve frontend scripts with vanilla JS.
• Don't require jQuery to be loaded in the frontend as a result of the above.

Trac ticket: https://core.trac.wordpress.org/ticket/54171

Adding a note that after these changes, the JS will no longer work correctly in IE 11. I'm not sure whether this is a concern, given that on the one hand we've deprecated it, but on the other hand we may want to preserve this theme working correctly in older versions of WordPress and their supported browsers.

@sgomes Thanks for the review! I've updated the code accordingly.

[flixos90]

Note that the implementation for this depends on whether we will drop IE support in the theme or not. The discussion around this should be centralized in https://core.trac.wordpress.org/ticket/55126#comment:2, which does the same for Twenty Sixteen.

[karmatosed]

As this has been sat for a little while I wanted to check-in how people are feeling about progressing this to close or coming up with a different resolution.

[karmatosed]

@flixos90 just raising up if you would like to still work on this? If not happy to either:

• Close this.
• Look to get steps on who can take this on.

[flixos90]

@karmatosed This, like the other similar tickets, is still something I would like to pursue. This has gotten a bit stale, since at this point it would probably make more sense to replace jQuery with using the Interactivity API, rather than vanilla JS. But this ticket makes sense to still be used for that.

I saw the similar Twenty Sixteen ticket was closed recently, I'd like to eventually reopen it for the same reason.

cc @adamsilverstein

[karmatosed]

@flixos90 I am more than happy to reopen the Twenty Sixteen one also if you want to have ownership of it and move it on. Would that be something you want to facilitate?

[flixos90]

@karmatosed Thank you, yes that would be great. Please feel free to assign me as owner for now.

[karmatosed]

Amazing, thank you @flixos90 and please let me know if there are any other tickets like that I can re-open or assign to you. Whilst we are absolutely trying to focus down things in default themes, we shouldn't miss the opportunity to improve performance when you are offering to take it on.

[flixos90]

Per https://core.trac.wordpress.org/ticket/61027#comment:10, I'm going to update the purpose of this ticket slightly: With the Interactivity API available, we should focus these efforts on using the Interactivity API instead of vanilla JS as a replacement for jQuery.

As such, this will need a refresh. Please read the linked comment on the overarching ticket for additional context.