Rails: access controller instance variable in CoffeeScript or JavaScript asset file

Question

In Rails 3.1 it is not possible to access controller instance variables in an asset js.erb or coffee.erb file using syntax such as <%= @foo %>, where @foo is set in the c

Answer 1

a couple of ways I have done this in the past

put the data in hidden fields, access the data in js/coffee

# single value
<%= hidden_field_tag "foo_name", @foo.name, { :id => "foo-name" } %>
$('#foo-name').val();

# when the 'value' has multiple attributes
<%= hidden_field_tag "foo", @foo.id, { :id => "foo", "data-first-name" => @foo.first_name, "data-last-name" => @foo.last_name } %>
$foo = $('#foo')
console.log $foo.val()
console.log $foo.data("firstName")
console.log $foo.data("lastName")

another option: load data into js data structure in erb, access it from js/coffee

<% content_for(:head) do %>
    
<% end %>


# coffee
for foo in window.App.Data.fooList
    console.log "#{foo.id}, #{foo.first_name} #{foo.last_name}"

I am not a big fan of constructing javascript data from ruby in erb like this, something about it just feels wrong - it can be effective though

and another option: make an ajax call and get the data on-demand from the server

I am also interested in other ideas and approaches