ajax datasources: remove locally-cached 'option' HTML element during item unselection

[jayaddison]

This pull request includes a

• Bug fix
• New feature
• Translation

The following changes were made

• Remove locally-cached HTML <option> elements from the DOM when an AJAX-sourced item is unselected.
• This should allow the data received from AJAX-based (re)selections to be refreshed.

If this is related to an existing ticket, include a link to it as well.

May resolve #5391.
Based upon / may be combined with #6241.

[jayaddison]

This seems like a really smelly way to achieve multiple visits and actions on the select2 control. My JavaScript-fu isn't great, so there's almost certainly a better way to do this.

[jayaddison]

Moving this pull request into a 'draft' status; option groups (nested results) need to be handled too.

[jayaddison]

Moving this pull request into a 'draft' status; option groups (nested results) need to be handled too.

From testing locally: option groups do not result in the creation of nested HTML elements in the DOM-cached data; a flattened set of <option> elements are stored, the same as for flat datasources.

As a result: I don't think that any special-case handling is required for option groups, and I'll put this pull request back into a 'ready for review' state.

The testing methodology I used was to create a small Python script to generate dummy nested JSON data in the select2 data format and to run that every few seconds by using watch -n 2 python write_data.py to (re)write JSON data to file.

In combination with a basic test HTML page (loading JQuery and Select2 JS and CSS files) with a <select multiple> and some select2({ajax: ...}) configuration, and python -m http.server -b 127.0.0.1 to serve the data and HTML statically, that was enough to test some dynamic grouped result querying, selection, and unselection.