How to load javascript file from rails plugin

Question

I'm trying to create a plugin which is suppose to expose a javascript file, but I can't get it to load in my rails 5 application.

In my gem, I've tried adding my javascript file called my_gem.js to

vendor/assets/javascripts
app/assets/javascripts
lib/<gem-name>/assets/javascripts

But none of them work. I just get this error message when loading the file in my application.js

couldn't find file 'my_gem' with type 'application/javascript'

This is how I load my plugin/gem in to my rails project

gem "my-gem", path: "~/projects/my-gem"

Richard Peck · Accepted Answer · 2016-01-12 12:57:13Z

1

We've created a gem which utilizes assets before.

You'll want to create an app/assets/javascripts/my_gem folder in your gem directory tree, where you'll put your my_gem.js file.

Most importantly, you need to add this file to the asset path (we use an engine):

#lib/my_gem.rb
module MyGem
   class Gem < Rails::Engine
      config.assets.precompile += %w(my_gem/my_gem.js) 
   end
end

This will either allow the file to be used standalone, or as part of your app:

#app/assets/javascripts/application.js
//= require my_gem/my_gem

answered Jan 12, 2016 at 12:57

Richard Peck

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1 Comment

Linus Oleander Over a year ago

Thanks! Almost correct. Adding config.assets.precompile += %w(gem/file.js) to the engine.rb exposes the file.js file meaning that //= require file should used, not //= require gem/file.

Wizard of Ogz · Accepted Answer · 2016-01-12 05:40:32Z

1

You must tell Rails to compile my_gem.js. You can do this in an initializer, application.rb, or environment file.

  Rails.application.config.assets.precompile += ["my_gem.js"]

I'd recommend keeping the source file at ~/projects/my-gem/app/assets/javascripts/my_gem.js

answered Jan 12, 2016 at 5:40

Wizard of Ogz

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6 Comments

Richard Peck Over a year ago

I upvoted although the above code needs to be in the gem, not the app ;)

Wizard of Ogz Over a year ago

An initializer can be in the gem

Richard Peck Over a year ago

Yes of course; I thought your answer was ambiguous on the point though

Wizard of Ogz Over a year ago

Here is information about adding an initializer in your gem (assuming it is a Rails Engine) link

Wizard of Ogz Over a year ago

ah, OK. Thanks for clarifying

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