Remove jQuery

[ArtOfCode-]

Removes the jQuery dependency from our code - see #1429.

WIP: Re-write scripts to use vanilla JS instead of jQuery.

Once scripts are rewritten we can remove the dependency itself.

Help wanted!

TODO LIST - please tick a file if you're about to review & update it so we don't duplicate work.

• [x] micro_auth/apps.js
• [x] admin.js
• [x] application.js
• [x] caret.js (utility, no update needed)
• [ ] categories.js
• [ ] character_count.js
• [x] closure.js
• [x] codeblocks.js
• [ ] comments.js
• [ ] donations.js
• [ ] embed.js
• [ ] filters.js
• [ ] flags.js
• [ ] keyboard_tools.js
• [x] latex_escape.js (utility, update not required)
• [ ] licenses.js
• [ ] markdown.js
• [x] mod_warning.js
• [x] modals.js
• [ ] moderator.js
• [ ] notifications.js
• [ ] post_histories.js
• [ ] posts.js
• [ ] preferences.js
• [ ] privileges.js
• [ ] qpixel_api.js
• [x] qpixel_dom.js
• [ ] reactions.js
• [ ] search.js
• [ ] site_settings.js
• [ ] subscriptions.js
• [ ] suggested_edits.js
• [ ] tag_sets.js
• [ ] tags.js
• [ ] textarea_popup.js
• [ ] tour.js
• [ ] two_factor.js
• [ ] users.js
• [ ] votes.js

[ArtOfCode-]

Slight roadblock: rails-ujs also depends on jQuery. This powers things like remote links/forms, which we use a bunch of. It's not impossible to replace, but it's a bunch more work.

My strategy at the moment is going to be to start by converting everything that doesn't use rails-ujs, leaving those bits as jQuery for the moment.

[ArtOfCode-]

Roadblock number 2: we use select2 for our interactive <select> elements, which is a jQuery plugin.

[ArtOfCode-]

Merging so this work doesn't just fester & we can continue to remove jQuery as we go.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.28%. Comparing base (2cea3f4) to head (2aab60a). Report is 16 commits behind head on develop.

Additional details and impacted files

Components	Coverage Δ
controllers	59.24% <ø> (ø)
helpers	68.18% <ø> (ø)
jobs	28.00% <ø> (ø)
models	80.09% <ø> (ø)

:umbrella: View full report in Codecov by Sentry.
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