How do I get escape_javascript and other helpers in my sprockets pre-processed js file (not a view)?

Question

I'm using Rails 3.1 and the sprockets stuff.

I want to use ERB to pre-process a js file that will then be included using javascript_include_tag. It is generated from code, and so I'm pre-processing it with ERB, but I can't get to the helpers like escape_javascript from ActionView::Helpers::JavaScriptHelper

Say my file is called dynamic.js.erb, and it contains

obj = {
 name: "test",
 tag: "<%= escape_javascript( image_tag( "logo.png" ) )%>"
};

How do I stop it from producing the error:

throw Error("NoMethodError: undefined method `escape_javascript' for #<#<Class:0x1067da940>:0x116b2be18>
(in /Users/me/site/app/assets/javascripts/dynamic.js.erb)")

When I hit my local server and ask for /assets/dynamic.js

Answer 1

You can include the rails JS helpers into your own class.

class Helper
  include ActionView::Helpers::JavaScriptHelper

  def self.escape_js( text )
    @instance ||= self.new
    return @instance.escape_javascript( text )
  end
end

Then use it in your ERB file:

obj = {
 name: "test",
 tag: "<%= Helper.escape_js( image_tag( "logo.png" ) ) )%>"
};

Answer 2

Call it through ActionController::Base.helpers like this:

// file.js.erb
var x = "<%= ActionController::Base.helpers.j image_tag('logo.png') %>";

Note that j is an alias for escape_javascript, so you can use the long name if you prefer.

Answer 3

You may also either include JavaScriptHelper directly into the Sprockets Context class (the class that runs your template):

<% environment.context_class.instance_eval { include ActionView::Helpers::JavaScriptHelper } %>

Or even define your helper somewhere else and include that in the template (so as to be able and reuse the helper)

<% environment.context_class.instance_eval { include MyHelper } %>