"If you load both jquery_ujs and rails-ujs, use rails-ujs only." when rails-ujs imported twice

[tai2]

Steps to reproduce

You use two JS bundles on a page and both of them import rails-ujs.
In addition to that, that page exposes jQuery in the global space.

// bundle_a.js
import { csrfToken } from 'rails-ujs'
...

// bundle_b.js
import { csrfToken } from 'rails-ujs'
...

<!-- page.html.erb -->
<script src="jquery-3.5.1.min.js"></script>
<script src="bundle_a.js" />
<script src="bundle_b.js" />

Expected behavior

• No runtime error
• You can import rails-ujs in each JS bundle
• You can use csrfToken() in each JS bundle

Actual behavior

page.html.erb crush with a runtime error which says 'If you load both jquery_ujs and rails-ujs, use rails-ujs only.

The line throws this error is here:

rails/actionview/app/assets/javascripts/rails-ujs/start.coffee

Lines 13 to 15 in 53331b4

	if jQuery? and jQuery.ajax?
	throw new Error('If you load both jquery_ujs and rails-ujs, use rails-ujs only.') if jQuery.rails
	jQuery.rails = Rails

System configuration

Rails version:
5.2.4.3

Ruby version:

2.6.5

[tai2]

I guess moving these 5 lines under Rails.start function mitigates this problem.

rails/actionview/app/assets/javascripts/rails-ujs/start.coffee

Lines 13 to 17 in 53331b4

	if jQuery? and jQuery.ajax?
	throw new Error('If you load both jquery_ujs and rails-ujs, use rails-ujs only.') if jQuery.rails
	jQuery.rails = Rails
	jQuery.ajaxPrefilter (options, originalOptions, xhr) ->
	CSRFProtection(xhr) unless options.crossDomain

However, this change corrupts apps that uses jQuery.rails without calling Rails.start.

[tai2]

This behavior was from 9df747c

[tahsin352]

I remove the jquery and its working properly

<%= javascript_pack_tag 'bundle_a' %>
<%= javascript_pack_tag 'bundle_b' %>

[tai2]

Yes, of course. It means you cannot use rails-ujs with jquery(or you can use it a limited way).

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
If you can still reproduce this error on the 6-1-stable branch or on main, please reply with all of the information you have about it in order to keep the issue open.
Thank you for all your contributions.