chatroom_channel.rb

class ChatroomChannel < ApplicationCable::Channel
  
    CHANNEL_NAME_TPL = "channel_%s"
  
    # Define a periodical
    periodically :check_pings, every: 10.seconds

    def subscribed
      _add_to_current_chats({
        id: params[:chat_id],
        users: [
          {
            connection_id: params[:connection_id],
            last_updated: DateTime.now.to_i
          }
        ]
      })
    end

    # This is the hearbeat's check function
    def check_pings
        # Fetch the list of current chats with the users. We use redis, you can use db as well.
        current_chats = _fetch_a_list_of_current_chats()
      
        current_chats.each do |chat|
          time_diff = DatetTime.now.to_i - chat.last_updated.to_i
          if time_diff > 3600
            # Clear this call from current calls, probably, it's just left there some reason
          end
          chat.users.each do |user|
            single_user_time_diff = DateTime.now.to_i - user.last_updated
            if singler_user_time_diff > 20
              # Do some something as the diff is longer
              ActionCable.server.broadcast CHANNEL_NAME_TPL % [chat.id], {msg: "user is dropped"}
            end
            if singler_user_time_diff > 10
              # Do some something as the diff is longer
              ActionCable.server.broadcast CHANNEL_NAME_TPL % [chat.id], {msg: "user is late"}
            end
          end
        end
    end
  
    def ping
      # It's the ping method used by the client side.
      chat = _fetch_chat(params[:chat_id])
      # Find the user
      chat.users.each do |user|
        if user.connectionId == params[:connection_id]
          # Update it's last ping time
          user.last_updated = DateTime.now.to_i
        end
      end
      _save_chat(chat)
    end
end

client.js

ConnectionMonitor = function(chat_id, connection_id) {
  this.cableConnection = ActionCable.createConsumer("/cable");
  this.subscription = null;
  var self = this;
  this.start = function() {
    // Create a cable subscription
    this.subscription = this.cableConnection.subscriptions.create({
      channel: "chatroom",
      chat_id: chat_id,
      connection_id: connection_id
      }, {
        connected: function() {
          // Once connection is established, start calling ping method of the channel periodically
          setInterval(function() {
            self.subscription.perform('ping', {
              // Those values should be kept somewhere in the client side, for drops on the backend side.
              chat_id: chat.id,
              connection_id: chat.connection_id
            });
            }, 5000);
        }
      })
  }
}
var monitor = new ConnectionMonitor("chat_id", "connection_id_of_this_user");
monitor.start();