polyglot/app/javascript/packs/chatrooms.js

import ActionCable from 'actioncable'

// create App object with key cable == new cosumer
(function() {
  window.App || (window.App = {});

  App.cable = ActionCable.createConsumer();

}).call(this);

// find chatroom id
const chatroomId = document.getElementById('chatroom-hook').dataset["chatroomId"]

// create subsciptions
App['chatroom' + chatroomId] = App.cable.subscriptions.create({
  channel: 'ChatRoomsChannel',
  room: chatroomId
}, {
  connected: () => {
  },
  received: data => {
    console.log(data)
  }
})

// Testing ActionCable
const testBtn = document.getElementById('test-btn')
testBtn.addEventListener('click', event => {
  fetch(`/chat_rooms/${chatroomId}/cable_testing` , {
    method: 'POST',
    body: JSON.stringify({})
  })
})