Automatically add 'needsclick' class to Drupal generated AJAX elements

Why this would be useful?

One reason it might be useful: FastClick prevents the Closed Question module (which relies on AJAX for answer submission and feedback display) from functioning properly on touch devices, as I describe at #2217621: Allow disabling init code per content type. It is quite possible that it interferes with other contrib modules that use AJAX, and it is quite possible that LewisNyman's idea would resolve such problems.

FastClick works by firing click at the same time as touchend, so it's possible that conflicts with touchend might arise.

https://github.com/ftlabs/fastclick#use-case-1-non-synthetic-click-required

Are there steps to reproduce so that we could inspect what's happening and figure out how widespread this problem is within core or Views or whatever?

This is indeed an issue with the default handling attached to ajax submit, button, and image_button elements, which prevents these elements from responding to a 'click' event on touch devices, if FastClick is installed.

Drupal's native ajax system uses the 'mousedown' event on ajax submit, button, and image_button elements instead of the 'click' event (see here), and then prevents the 'click' event from firing (see here). This all happens in ajax_pre_render_element().

You can, of course, bypass this by explicitly setting the 'event' property to 'click', or setting the 'prevent' property to something other than 'click'. But most modules don't do this. We're experiencing this with Webform Stripe.

This issue describes why 'mousedown' was added in the first place:
#216059: AHAH triggered by text input enter key press, breaks e.g. autocomplete

This issue describes what problems were introduced after above was committed:
#634616: Various problems due to AJAX binding to mousedown instead of click

A very simple workaround in the FastClick module would be to add process callbacks to these three elements, and in that callback check if the 'click' event is being prevented. If so, add the 'needsclick' class to the element. Simple!

Applied to dev, thanks!

Thanks! I supposed we can mark this as fixed then. :)