Allow extractElementAttributes to use a checkbox list

[julianrubisch]

Feature Request

extractElementAttributes for the moment returns multiple values for select tags with multiple: true:

https://github.com/hopsoft/stimulus_reflex/blob/480ee76dccf4ddc212602d1c3dee01216b6369ab/javascript/attributes.js#L37

A common scenario is to use a checkbox list for an association collection, as in collection_check_boxes:

https://devdocs.io/rails~6.0/actionview/helpers/formoptionshelper#method-i-collection_check_boxes

It would be nice if SR supported that out of the box.

Describe the solution you'd like

The hidden complexity lies in the fact that we'd have to consider multiple elements in extractElementAttributes, not just the one triggering the reflex. Still I think a library such as SR should take on that complexity instead of imposing it on the back end developer.

Specifically, I discovered this shortage when working on the permalink expo example and trying to employ a button group: https://github.com/hopsoft/stimulus_reflex_expo/pull/26/files#diff-23c58647594fccfb30d0b54554851d59R15

[hopsoft]

Are you thinking we should marshal attributes only for checked and selected options? Then store them under something like attrs.checkedOptions = [{...},{...},...] and attrs.selectedOptions = [{...},{...},...]?

[julianrubisch]

Right. On the server side you’d get an array of checked options as in a multiple select