Common Constants

common_constants.rb

# Share constants between ruby and javascript
# Setup
# (in application.html.erb, or some place to inject javascript)
# MyApplication.constants = #{CommonConstants.to_json};
# 
# Usage
# Ruby
#   CommonConstants << "Math::PI"
# Javascript
#   MyApplication.constants.MATH_PI

module CommonConstants
  extend self
  def to_json
    Hash[constants.map do |const_name, value|
      [json_name_for_const(const_name), value]
    end].to_json
  end

  def constants
    @constants ||= {}
  end

  def <<(const_name)
    const_value = Object.const_get(const_name)
    constants[const_name] = const_value
  end

  def json_name_for_const(const_name)
    const_name
      .split("::")
      .map(&:underscore)
      .map(&:upcase)
      .join("_")
  end
end