Refactor (if feasible) uses of the jQuery trigger function to use vanillaJS

So part of this issue is about having a linting rule put in place to ensure that new code added to Drupal does not implement jQuery's .trigger method AND the same rule provides a nice checklist of all the places where Drupal core is currently implementing that method. That's a good piece of foundational / platform support for ensuring we're reducing our jQuery footprint.

That's part of, but not all of, the main goal here. The main goal is to actually reduce jQuery's footprint by removing all the instances of the method. Once that's done, we can close the door on adding new code that uses that part of jQuery. Then we're done.

In my opinion, we are currently unblocked from making progress in that area. So i'm going to hack on this idea a bit.

Current output of yarn lint:core-js-passing when the jquery/no-trigger rule is enabled:

/var/www/html/web/core/misc/ajax.js
   584:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   585:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   587:17  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   744:7   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  1101:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/details.js
  21:5  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/dialog/dialog.ajax.js
   38:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   42:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  102:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  102:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  102:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/dialog/dialog.jquery-ui.js
  72:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/dialog/dialog.js
  73:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  76:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  80:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  84:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/dialog/dialog.position.js
  125:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/dialog/off-canvas/js/off-canvas.js
  142:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  244:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/displace.js
  222:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/form.js
  147:5   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  292:7   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  298:24  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/machine-name.js
  190:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/states.js
  735:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  746:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/tabbingmanager.js
  181:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  248:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  367:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  382:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  396:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/tabledrag.js
  395:5   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  610:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  665:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  735:7   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/tableresponsive.js
   49:5   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  186:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/tableselect.js
  64:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  86:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/misc/vertical-tabs.js
  173:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/contextual/js/contextual.js
  135:5  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/editor/js/editor.admin.js
  30:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  46:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  65:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/editor/js/editor.dialog.js
  32:5  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/editor/js/editor.js
  305:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/field_ui/field_ui.js
   50:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   63:15  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  338:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/file/file.js
  198:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  214:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  278:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/filter/filter.js
  28:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/media_library/js/media_library.click_to_select.js
  29:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/media_library/js/media_library.ui.js
   65:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  336:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  373:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/media_library/js/media_library.view.js
  30:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/menu_ui/menu_ui.js
  80:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  81:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  90:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/node/node.preview.js
  97:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/settings_tray/js/settings_tray.js
   36:5   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   43:5   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  100:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  209:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  209:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/system/js/system.date.js
  60:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/system/js/system.js
  79:7  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/text/text.js
  68:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/toolbar/js/toolbar.js
  177:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  180:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  183:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/toolbar/tests/src/Nightwatch/Tests/toolbarTest.js
  241:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  254:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  304:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  308:9  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/tour/js/tour.js
  39:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/views_ui/js/ajax.js
  108:7   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  177:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/views_ui/js/dialog.views.js
  54:11  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/modules/views_ui/js/views-admin.js
   480:7   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   581:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
   622:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  1180:7   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  1246:9   error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  1259:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/tests/Drupal/Nightwatch/Tests/tabbableShimTest.js
  180:22  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger
  180:22  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/themes/claro/js/details.js
  24:13  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

/var/www/html/web/core/themes/claro/js/nav-tabs.js
  71:5  error  Prefer dispatchEvent to $.trigger  jquery/no-trigger

To fix, this guidance from stack overflow seems important: https://stackoverflow.com/questions/5658849/whats-the-equivalent-of-jque...

In this article, they (as as the linting error response) recommend using JavaScript's dispatchEvent method on the targeted element. What the stack overflow article mentions is that we can avoid potential problems by being thoughtful about what kind of Event we dispatch. Considering the careful creation and use of JavaScript Events, we are likely to discover that each use of .trigger('specific_event') has a sensible default replacement.

Let's create a list of all the different kinds of events we're currently triggering and figure out a dispatchEvent equivalent.

Found .triggers (excluding 3rd party js)

• focus
• formUpdated.machineName
• ajaxSuccess
• ajaxComplete
• ajaxStop
• summaryUpdated
• click
• mousedown
• mouseup
• dialog:beforecreate
• dialog:aftercreate
• dialog:beforeclose
• dialog:afterclose
• dialogContentResize
• resize.dialogResize
• resize.off-canvas
• dialogContentResize.off-canvas
• drupalViewportOffsetChange
• summaryUpdated
• formUpdated
• formFragmentLinkClickOrHashChange
• change
• drupalTabbingConstrained
• DrupalTabbingContextReleased
• DrupalTabbingContextActivated
• DrupalTabbingContextDeactivated
• blur
• drupalEditorFeatureAdded
• drupalEditorFeatureRemoved
• drupalEditorFeatureModified
• editor:dialogsave
• fileUpload
• change.filterGuidelines
• submit
• resize.tabs

A lot of these seem to be custom events. jQuery enumerates it's events as:

• blur
• change
• click
• contextmenu
• dblclick
• error
• focus
• hover
• keydown
• keypress
• keyup
• load
• mousedown
• mouseenter
• mouseleave
• mousemove
• mouseout
• mouseover
• mouseoff
• mouseup
• resize
• scroll
• select
• submit
• unload

When we use jQuery's list of events to reduce our list of found usages of .trigger we can reduce the list to:

• custom events we create
• focus
• click
• mousedown
• mouseup
• change
• blur
• submit
• resize?

Tricky bit might come into play when we need to stop using .trigger for jQuery events that we are overriding / extending. Best place to see what I mean here is to look at ajaxSuccess (all the ajax* "Events")

from ajax.es6.js, line 1768

$.extend(true, $.event.special, {
    ajaxSuccess: {
      trigger(event, xhr, settings) {
        if (stopEvent(xhr, settings)) {
          return false;
        }
      },
    },
    ajaxComplete: {
      trigger(event, xhr, settings) {
        if (stopEvent(xhr, settings)) {
          // jQuery decrements its internal active ajax counter even when we
          // stop the ajaxComplete event, but we don't want that counter
          // decremented, because for our purposes this request is still active
          // while commands are executing. By incrementing it here, the net
          // effect is that it remains unchanged. By remaining above 0, the
          // ajaxStop event is also prevented.
          $.active++;
          return false;
        }
      },
    },
  });

Perhaps that's a good place to start. We can itemize which usages have simple fixes and which have complex fixes.

Also, from @bnjmnm in Slack:

Anything event related such as trigger may have a little bit of additional complexity as we need to account for event listeners in contrib modules that expect the [, extraParameters ] arg http://api.jquery.com/trigger/. I'm pretty sure there are reasonable ways to hack around it though, and there's only upside to getting started on this even if that part isn't figured out yet.

Scanning core for all instances of $.extend returns > 50 files. Perhaps that's not a good search at the moment. Maybe we should take a stab at fixing these "easy" replacements and see how much is left aftwards.

To that end, how can we map the current "easy" uses .trigger to non-jquery solutions. In order to understand better how to provide developers a good replacement for what they currently have available with jQuery's event system let's focus on Focus.

Possible deprecation code comment / guidance we could provide

.trigger('focus') => .dispatchEvent(new FocusEvent('focus'))

Using an event object instead of doing something like $element.focus() allows the event system to properly bubble / propagate the event through the system.

When we use an Event object, JavaScript's event dispatcher triggers the event, allows any event handlers to do their actions, and when they're all done, finally focuses on the targeted element.

When .focus() is used, the targeted element immediately receives focus then the event handlers get notified of the event and they do their actions.

More research also uncovered a possible solution for the CustomEvent concern. Regarding:

Anything event related such as trigger may have a little bit of additional complexity as we need to account for event listeners in contrib modules that expect the [, extraParameters ] arg http://api.jquery.com/trigger/. I'm pretty sure there are reasonable ways to hack around it though, and there's only upside to getting started on this even if that part isn't figured out yet.

Even when we're using only JavaScript to define events we'll need to allow those events to define custom data to consume. We can do so using an Event's detail property:

// Create a custom event with type 'myEvent' and include custom options
var customEvent = new CustomEvent('myEvent', {
  detail: {
    options: [
      {
        name: "Option 1",
        value: "1"
      },
      {
        name: "Option 2",
        value: "2"
      }
    ]
  }
});

// Dispatch the custom event
document.getElementById("myButton").dispatchEvent(customEvent);

Considering all of the above, it appears that we're unblocked here. All this groundwork is all the time I have today to explore this question. I'll see if I can get back to this tonight to start hacking on a MR for some of these easy bits.

Maybe this is a silly question, but is this backwards compatible? How do jQuery events compare to events triggered through dispatchEvent()?

currently looking into this

I am facing issues with the PHP unit tests. I have attempted to fix some of the issues, but many remain, and some solutions are causing additional problems. It would be great if someone else could have a look at it.