Rails: about yield

Question

I saw some code in a Rails v2.3 app.

In layout/car_general.html.erb (this view is called by a method in cars_controller) , I saw the code:

<body>
    <%= yield %>

    <%= javascript_include_tag 'jquery-1.4.2.min' %>

    <% javascript_tag do %>
      <%= yield :jstemplates %>
          var some_car = new Object;
      <%= yield :some_car %>
    <% end -%>
</body>

Two questions to ask:

Where can I find the yield content of the first <%=yield%> under <body>.
Is it a rails specific way to include js code in a view by using <%= yield :jstemplates %> and what about <%= yield :some_car %> , is it point to a view or just to show the value of some_car?

score 63 · Accepted Answer · edited Mar 25 '17 at 14:03

Without any arguments, yield will render the template of the current controller/action. So if you're on the cars/show page, it will render views/cars/show.html.erb.

When you pass yield an argument, it lets you define content in your templates that you want to be rendered outside of that template. For example, if your cars/show page has a specific html snippet that you want to render in the footer, you could add the following to your show template and the car_general layout:

show.html.erb:

<% content_for :footer do %>
  This content will show up in the footer section
<% end %>

layouts/car_general.html.erb

<%= yield :footer %>

The Rails Guide has a good section on using yield and content_for: http://guides.rubyonrails.org/layouts_and_rendering.html#understanding-yield

The API documentation for content_for is helpful too and has some other examples to follow. Note that it's for Rails 3.1.1 , but this functionality has not changed much since 2.3, if at all and should still apply for 3.0.x and 3.1.x.

Rails: about yield

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