Capybara helper for defining a JavaScript function in a page (globally, attached to window)

define_function.rb

# Given the name and body for a JavaScript function, this defines the 
# function globally in the page.
#
# This is most useful for making helper JavaScript functions that you can 
# call later, eg. foo = evaluate_script('myFunction()')
#
# Usage:
#
#     page.define_function :whatever, %{
#       var foo = 'hello';
#       return foo;
#     }
#
#     result = page.evaluate_script('whatever()')
#
class Capybara::Session
  def define_function name, body
    execute_script %{
      window[#{name.to_s.inspect}] = function() {
        #{body}
      };
    }
  end
end