rails--rails/actioncable/app/assets/javascripts/action_cable/subscription.coffee

# A new subscription is created through the ActionCable.Subscriptions instance available on the consumer.
# It provides a number of callbacks and a method for calling remote procedure calls on the corresponding
# Channel instance on the server side.
#
# An example demonstrates the basic functionality:
#
#   App.appearance = App.cable.subscriptions.create "AppearanceChannel",
#     connected: ->
#       # Called once the subscription has been successfully completed
#
#     disconnected: ({ willAttemptReconnect: boolean }) ->
#       # Called when the client has disconnected with the server.
#       # The object will have an `willAttemptReconnect` property which
#       # says whether the client has the intention of attempting
#       # to reconnect.
#
#     appear: ->
#       @perform 'appear', appearing_on: @appearingOn()
#
#     away: ->
#       @perform 'away'
#
#     appearingOn: ->
#       $('main').data 'appearing-on'
#
# The methods #appear and #away forward their intent to the remote AppearanceChannel instance on the server
# by calling the `@perform` method with the first parameter being the action (which maps to AppearanceChannel#appear/away).
# The second parameter is a hash that'll get JSON encoded and made available on the server in the data parameter.
#
# This is how the server component would look:
#
#   class AppearanceChannel < ApplicationActionCable::Channel
#     def subscribed
#       current_user.appear
#     end
#
#     def unsubscribed
#       current_user.disappear
#     end
#
#     def appear(data)
#       current_user.appear on: data['appearing_on']
#     end
#
#     def away
#       current_user.away
#     end
#   end
#
# The "AppearanceChannel" name is automatically mapped between the client-side subscription creation and the server-side Ruby class name.
# The AppearanceChannel#appear/away public methods are exposed automatically to client-side invocation through the @perform method.
class ActionCable.Subscription
  constructor: (@consumer, params = {}, mixin) ->
    @identifier = JSON.stringify(params)
    extend(this, mixin)

  # Perform a channel action with the optional data passed as an attribute
  perform: (action, data = {}) ->
    data.action = action
    @send(data)

  send: (data) ->
    @consumer.send(command: "message", identifier: @identifier, data: JSON.stringify(data))

  unsubscribe: ->
    @consumer.subscriptions.remove(this)

  extend = (object, properties) ->
    if properties?
      for key, value of properties
        object[key] = value
    object