Question

In my assets, I have a file called maps.js.erb, basically with only the following (debugging) content:

alert("<%= @map.width %>");

This JS file is loaded through the show.html.erb view belonging to maps.

<%= javascript_include_tag params[:controller] %>
<h1><%= @map.title %></h1>
…

The HTML file itself shows the map’s title, e.g. when browsing to /maps/1/, since @map is defined in the controller. However, as soon as I include the JS file, I get the following error:

NoMethodError in Maps#show

Showing …/app/views/maps/show.html.erb where line #1 raised:

undefined method ‘title’ for nil:NilClass
(in …/app/assets/javascripts/maps.js.erb)

• Why is @map not available in the js.erb file?
• How else can I access this instance variable defined in my controller?

Answer 1

Ryan Bates did a screencast right on that topic – you might wanna check it out:

http://railscasts.com/episodes/324-passing-data-to-javascript

---

In the html.erb file, you can define the variables:

<%= javascript_tag do %>
  window.productsURL = "<%=j products_url %>";
  window.products = <%=raw Product.limit(10).to_json %>;
<% end %>