Access instance variable through coffeescript

Question

I'm trying to access some ruby instance variables through a coffeescript file. At what point do instance variables become defined? For example, when I try the following:

$(window).load () ->    
 $('#s3-uploader').S3Uploader
    additional_data: {project_id: <%= @project.id %>, step_id: <%= @step.id %>, user_id: <%= current_user.id %>}

I get the error

Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id
  (in /images.js.coffee.erb)

I know that @project should be defined, though, since I use it on the page when it's loaded. What am I doing wrong?

Amadan · Accepted Answer · 2014-01-28 06:41:29Z

1

Your CoffeeScript and your page are most likely in different views. Thus, having @project available when rendering your page says nothing about its availability when you're rendering your JavaScript. The easiest way to transfer this is to define a JavaScript variable inside your page view. For instance, if you're using Haml or Slim:

coffeescript:
  window.MyModule.project_id = #{ @project.id }

and then change your code to

additional_data: { project_id: window.MyModule.project_id, ... }

answered Jan 28, 2014 at 6:41

Amadan

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2 Comments

scientiffic Over a year ago

Thanks for your advice. If my page is loaded via a partial, how would I define the project_id variable? Would it be something like <script>window.MyModule.project_id = <%[email protected]%></script> ?

Amadan Over a year ago

Doesn't matter if it's partial or not, but what engine you're using. If you're using ERb (as it seems), then yes. Given that you're writing in regular JavaScript and not CoffeeScript, a semicolon would be advisable (even though unnecessary) as good JS style.

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