Is `require jquery_ujs` still needed in Rails 5.1?

Question

I am installing jQuery in my 5.1.x Rails app via the jquery-rails gem.

In the gem setup, they recommend to add these lines to application.js by default:

//= require jquery
//= require jquery_ujs

But, in a Rails 5.1.x app, you have already this line which doesn't depend on jQuery anymore:

//= require rails-ujs

I suppose both are doing the exact same thing and one is not needed.

Should I keep both anyway or should I prefer only jquery_ujs or only rails-ujs?

Answer 1

jquery-ujs is a thing of the past as of Rails 5.1, you don't need it.

Answer 2

As of Rails 5.1 jQuery is no longer required for UJS (unobtrusive javascript). So if you have no need of jQuery in your rails app, you can just use

//= require rails-ujs

On the other hand, if you do use jQuery in your app, and use the jquery-rails gem, and you should NOT require rails-ujs, but should instead use:

//= require jquery
//= require jquery_ujs

Requiring jquery_ujs along with jQuery can cause issues in the app, and you may see the following JS console error:

Uncaught Error: jquery-ujs has already been loaded!