Convert ActionCable javascript to ES2015 modules with modern build environment

We've replaced the sprockets `//= require` directives with ES2015
imports. As a result, the ActionCable javascript can now be compiled
with rollup (like ActiveStorage already is).

- Rename action_cable/index.js.erb -> action_cable/index.js

- Add rake task to generate a javascript module of the ActionCable::INTERNAL ruby hash

  This will allow us to get rid of ERB from the actioncable javascript,
  since it is only used to interpolate ActionCable::INTERNAL.to_json.

- Import INTERNAL directly in ActionCable Connection module

  This is necessary to remove a load-order dependency conflict in the
  rollup-compiled build. Using ActionCable.INTERNAL would result in a
  runtime error:
  ```
  TypeError: Cannot read property 'INTERNAL' of undefined
  ```
  because ActionCable.INTERNAL is not set before the Connection module
  is executed.

  All other ActionCable.* references are executed inside of the body of a
  function, so there is no load-order dependency there.

- Add eslint and eslint-plugin-import devDependencies to actioncable

  These will be used to add a linting setup to actioncable like the one
  in activestorage.

- Add .eslintrc to actioncable

  This lint configuration was copied from activestorage

- Add lint script to actioncable

  This is the same as the lint script in activestorage

- Add babel-core, babel-plugin-external-helpers, and babel-preset-env devDependencies to actioncable

  These will be used to add ES2015 transpilation support to actioncable
  like we have in activestorage.

- Add .babelrc to actioncable

  This configuration was copied from activestorage

- Enable loose mode in ActionCable's babel config

  This generates a smaller bundle when compiled

- Add rollup devDependencies to actioncable

  These will be used to add a modern build pipeline to actioncable like
  the one in activestorage.

- Add rollup config to actioncable

  This is essentially the same as the rollup config from activestorage

- Add prebuild and build scripts to actioncable package

  These scripts were copied from activestorage

- Invoke code generation task as part of actioncable's prebuild script

  This will guarantee that the action_cable/internal.js module is
  available at build time (which is important, because two other modules
  now depend on it).

- Update actioncable package to reference the rollup-compiled files

  Now that we have a fully functional rollup pipeline in actioncable, we
  can use the compiled output in our npm package.

- Remove build section from ActionCable blade config

  Now that rollup is responsible for building ActionCable, we can remove
  that responsibility from Blade.

- Remove assets:compile and assets:verify tasks from ActionCable

  Now that we've added a compiled ActionCable bundle to version control,
  we don't need to compile and verify it at publish-time.

  (We're following the pattern set in ActiveStorage.)

- Include compiled ActionCable javascript bundle in published gem

  This is necessary to maintain support for depending on the ActionCable
  javascript through the Sprockets asset pipeline.

- Add compiled ActionCable bundle to version control

  This mirrors what we do in ActiveStorage, and allows ActionCable to
  continue to be consumed via the sprockets-based asset pipeline when
  using a git source instead of a published version of the gem.

7 files changed, 736 insertions, 256 deletions

diff --git a/actioncable/app/assets/javascripts/action_cable.js b/actioncable/app/assets/javascripts/action_cable.js
new file mode 100644
index 0000000000..df60b1fc24
--- /dev/null
+++ b/actioncable/app/assets/javascripts/action_cable.js
@@ -0,0 +1,475 @@
+(function(global, factory) {
+  typeof exports === "object" && typeof module !== "undefined" ? module.exports = factory() : typeof define === "function" && define.amd ? define(factory) : global.ActionCable = factory();
+})(this, function() {
+  "use strict";
+  var INTERNAL = {
+    message_types: {
+      welcome: "welcome",
+      ping: "ping",
+      confirmation: "confirm_subscription",
+      rejection: "reject_subscription"
+    },
+    default_mount_path: "/cable",
+    protocols: [ "actioncable-v1-json", "actioncable-unsupported" ]
+  };
+  var _typeof = typeof Symbol === "function" && typeof Symbol.iterator === "symbol" ? function(obj) {
+    return typeof obj;
+  } : function(obj) {
+    return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj;
+  };
+  var classCallCheck = function(instance, Constructor) {
+    if (!(instance instanceof Constructor)) {
+      throw new TypeError("Cannot call a class as a function");
+    }
+  };
+  var message_types = INTERNAL.message_types, protocols = INTERNAL.protocols;
+  var supportedProtocols = protocols.slice(0, protocols.length - 1);
+  var indexOf = [].indexOf;
+  var Connection = function() {
+    function Connection(consumer) {
+      classCallCheck(this, Connection);
+      this.open = this.open.bind(this);
+      this.consumer = consumer;
+      this.subscriptions = this.consumer.subscriptions;
+      this.monitor = new ActionCable.ConnectionMonitor(this);
+      this.disconnected = true;
+    }
+    Connection.prototype.send = function send(data) {
+      if (this.isOpen()) {
+        this.webSocket.send(JSON.stringify(data));
+        return true;
+      } else {
+        return false;
+      }
+    };
+    Connection.prototype.open = function open() {
+      if (this.isActive()) {
+        ActionCable.log("Attempted to open WebSocket, but existing socket is " + this.getState());
+        return false;
+      } else {
+        ActionCable.log("Opening WebSocket, current state is " + this.getState() + ", subprotocols: " + protocols);
+        if (this.webSocket) {
+          this.uninstallEventHandlers();
+        }
+        this.webSocket = new ActionCable.WebSocket(this.consumer.url, protocols);
+        this.installEventHandlers();
+        this.monitor.start();
+        return true;
+      }
+    };
+    Connection.prototype.close = function close() {
+      var _ref = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {
+        allowReconnect: true
+      }, allowReconnect = _ref.allowReconnect;
+      if (!allowReconnect) {
+        this.monitor.stop();
+      }
+      if (this.isActive()) {
+        return this.webSocket ? this.webSocket.close() : undefined;
+      }
+    };
+    Connection.prototype.reopen = function reopen() {
+      ActionCable.log("Reopening WebSocket, current state is " + this.getState());
+      if (this.isActive()) {
+        try {
+          return this.close();
+        } catch (error) {
+          ActionCable.log("Failed to reopen WebSocket", error);
+        } finally {
+          ActionCable.log("Reopening WebSocket in " + this.constructor.reopenDelay + "ms");
+          setTimeout(this.open, this.constructor.reopenDelay);
+        }
+      } else {
+        return this.open();
+      }
+    };
+    Connection.prototype.getProtocol = function getProtocol() {
+      return this.webSocket ? this.webSocket.protocol : undefined;
+    };
+    Connection.prototype.isOpen = function isOpen() {
+      return this.isState("open");
+    };
+    Connection.prototype.isActive = function isActive() {
+      return this.isState("open", "connecting");
+    };
+    Connection.prototype.isProtocolSupported = function isProtocolSupported() {
+      return indexOf.call(supportedProtocols, this.getProtocol()) >= 0;
+    };
+    Connection.prototype.isState = function isState() {
+      for (var _len = arguments.length, states = Array(_len), _key = 0; _key < _len; _key++) {
+        states[_key] = arguments[_key];
+      }
+      return indexOf.call(states, this.getState()) >= 0;
+    };
+    Connection.prototype.getState = function getState() {
+      if (this.webSocket) {
+        for (var state in WebSocket) {
+          if (WebSocket[state] === this.webSocket.readyState) {
+            return state.toLowerCase();
+          }
+        }
+      }
+      return null;
+    };
+    Connection.prototype.installEventHandlers = function installEventHandlers() {
+      for (var eventName in this.events) {
+        var handler = this.events[eventName].bind(this);
+        this.webSocket["on" + eventName] = handler;
+      }
+    };
+    Connection.prototype.uninstallEventHandlers = function uninstallEventHandlers() {
+      for (var eventName in this.events) {
+        this.webSocket["on" + eventName] = function() {};
+      }
+    };
+    return Connection;
+  }();
+  Connection.reopenDelay = 500;
+  Connection.prototype.events = {
+    message: function message(event) {
+      if (!this.isProtocolSupported()) {
+        return;
+      }
+      var _JSON$parse = JSON.parse(event.data), identifier = _JSON$parse.identifier, message = _JSON$parse.message, type = _JSON$parse.type;
+      switch (type) {
+       case message_types.welcome:
+        this.monitor.recordConnect();
+        return this.subscriptions.reload();
+
+       case message_types.ping:
+        return this.monitor.recordPing();
+
+       case message_types.confirmation:
+        return this.subscriptions.notify(identifier, "connected");
+
+       case message_types.rejection:
+        return this.subscriptions.reject(identifier);
+
+       default:
+        return this.subscriptions.notify(identifier, "received", message);
+      }
+    },
+    open: function open() {
+      ActionCable.log("WebSocket onopen event, using '" + this.getProtocol() + "' subprotocol");
+      this.disconnected = false;
+      if (!this.isProtocolSupported()) {
+        ActionCable.log("Protocol is unsupported. Stopping monitor and disconnecting.");
+        return this.close({
+          allowReconnect: false
+        });
+      }
+    },
+    close: function close(event) {
+      ActionCable.log("WebSocket onclose event");
+      if (this.disconnected) {
+        return;
+      }
+      this.disconnected = true;
+      this.monitor.recordDisconnect();
+      return this.subscriptions.notifyAll("disconnected", {
+        willAttemptReconnect: this.monitor.isRunning()
+      });
+    },
+    error: function error() {
+      ActionCable.log("WebSocket onerror event");
+    }
+  };
+  var now = function now() {
+    return new Date().getTime();
+  };
+  var secondsSince = function secondsSince(time) {
+    return (now() - time) / 1e3;
+  };
+  var clamp = function clamp(number, min, max) {
+    return Math.max(min, Math.min(max, number));
+  };
+  var ConnectionMonitor = function() {
+    function ConnectionMonitor(connection) {
+      classCallCheck(this, ConnectionMonitor);
+      this.visibilityDidChange = this.visibilityDidChange.bind(this);
+      this.connection = connection;
+      this.reconnectAttempts = 0;
+    }
+    ConnectionMonitor.prototype.start = function start() {
+      if (!this.isRunning()) {
+        this.startedAt = now();
+        delete this.stoppedAt;
+        this.startPolling();
+        document.addEventListener("visibilitychange", this.visibilityDidChange);
+        ActionCable.log("ConnectionMonitor started. pollInterval = " + this.getPollInterval() + " ms");
+      }
+    };
+    ConnectionMonitor.prototype.stop = function stop() {
+      if (this.isRunning()) {
+        this.stoppedAt = now();
+        this.stopPolling();
+        document.removeEventListener("visibilitychange", this.visibilityDidChange);
+        ActionCable.log("ConnectionMonitor stopped");
+      }
+    };
+    ConnectionMonitor.prototype.isRunning = function isRunning() {
+      return this.startedAt && !this.stoppedAt;
+    };
+    ConnectionMonitor.prototype.recordPing = function recordPing() {
+      this.pingedAt = now();
+    };
+    ConnectionMonitor.prototype.recordConnect = function recordConnect() {
+      this.reconnectAttempts = 0;
+      this.recordPing();
+      delete this.disconnectedAt;
+      ActionCable.log("ConnectionMonitor recorded connect");
+    };
+    ConnectionMonitor.prototype.recordDisconnect = function recordDisconnect() {
+      this.disconnectedAt = now();
+      ActionCable.log("ConnectionMonitor recorded disconnect");
+    };
+    ConnectionMonitor.prototype.startPolling = function startPolling() {
+      this.stopPolling();
+      this.poll();
+    };
+    ConnectionMonitor.prototype.stopPolling = function stopPolling() {
+      clearTimeout(this.pollTimeout);
+    };
+    ConnectionMonitor.prototype.poll = function poll() {
+      var _this = this;
+      this.pollTimeout = setTimeout(function() {
+        _this.reconnectIfStale();
+        _this.poll();
+      }, this.getPollInterval());
+    };
+    ConnectionMonitor.prototype.getPollInterval = function getPollInterval() {
+      var _constructor$pollInte = this.constructor.pollInterval, min = _constructor$pollInte.min, max = _constructor$pollInte.max;
+      var interval = 5 * Math.log(this.reconnectAttempts + 1);
+      return Math.round(clamp(interval, min, max) * 1e3);
+    };
+    ConnectionMonitor.prototype.reconnectIfStale = function reconnectIfStale() {
+      if (this.connectionIsStale()) {
+        ActionCable.log("ConnectionMonitor detected stale connection. reconnectAttempts = " + this.reconnectAttempts + ", pollInterval = " + this.getPollInterval() + " ms, time disconnected = " + secondsSince(this.disconnectedAt) + " s, stale threshold = " + this.constructor.staleThreshold + " s");
+        this.reconnectAttempts++;
+        if (this.disconnectedRecently()) {
+          ActionCable.log("ConnectionMonitor skipping reopening recent disconnect");
+        } else {
+          ActionCable.log("ConnectionMonitor reopening");
+          this.connection.reopen();
+        }
+      }
+    };
+    ConnectionMonitor.prototype.connectionIsStale = function connectionIsStale() {
+      return secondsSince(this.pingedAt ? this.pingedAt : this.startedAt) > this.constructor.staleThreshold;
+    };
+    ConnectionMonitor.prototype.disconnectedRecently = function disconnectedRecently() {
+      return this.disconnectedAt && secondsSince(this.disconnectedAt) < this.constructor.staleThreshold;
+    };
+    ConnectionMonitor.prototype.visibilityDidChange = function visibilityDidChange() {
+      var _this2 = this;
+      if (document.visibilityState === "visible") {
+        setTimeout(function() {
+          if (_this2.connectionIsStale() || !_this2.connection.isOpen()) {
+            ActionCable.log("ConnectionMonitor reopening stale connection on visibilitychange. visbilityState = " + document.visibilityState);
+            _this2.connection.reopen();
+          }
+        }, 200);
+      }
+    };
+    return ConnectionMonitor;
+  }();
+  ConnectionMonitor.pollInterval = {
+    min: 3,
+    max: 30
+  };
+  ConnectionMonitor.staleThreshold = 6;
+  var Consumer = function() {
+    function Consumer(url) {
+      classCallCheck(this, Consumer);
+      this.url = url;
+      this.subscriptions = new ActionCable.Subscriptions(this);
+      this.connection = new ActionCable.Connection(this);
+    }
+    Consumer.prototype.send = function send(data) {
+      return this.connection.send(data);
+    };
+    Consumer.prototype.connect = function connect() {
+      return this.connection.open();
+    };
+    Consumer.prototype.disconnect = function disconnect() {
+      return this.connection.close({
+        allowReconnect: false
+      });
+    };
+    Consumer.prototype.ensureActiveConnection = function ensureActiveConnection() {
+      if (!this.connection.isActive()) {
+        return this.connection.open();
+      }
+    };
+    return Consumer;
+  }();
+  var extend = function extend(object, properties) {
+    if (properties != null) {
+      for (var key in properties) {
+        var value = properties[key];
+        object[key] = value;
+      }
+    }
+    return object;
+  };
+  var Subscription = function() {
+    function Subscription(consumer) {
+      var params = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {};
+      var mixin = arguments[2];
+      classCallCheck(this, Subscription);
+      this.consumer = consumer;
+      this.identifier = JSON.stringify(params);
+      extend(this, mixin);
+    }
+    Subscription.prototype.perform = function perform(action) {
+      var data = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {};
+      data.action = action;
+      return this.send(data);
+    };
+    Subscription.prototype.send = function send(data) {
+      return this.consumer.send({
+        command: "message",
+        identifier: this.identifier,
+        data: JSON.stringify(data)
+      });
+    };
+    Subscription.prototype.unsubscribe = function unsubscribe() {
+      return this.consumer.subscriptions.remove(this);
+    };
+    return Subscription;
+  }();
+  var Subscriptions = function() {
+    function Subscriptions(consumer) {
+      classCallCheck(this, Subscriptions);
+      this.consumer = consumer;
+      this.subscriptions = [];
+    }
+    Subscriptions.prototype.create = function create(channelName, mixin) {
+      var channel = channelName;
+      var params = (typeof channel === "undefined" ? "undefined" : _typeof(channel)) === "object" ? channel : {
+        channel: channel
+      };
+      var subscription = new ActionCable.Subscription(this.consumer, params, mixin);
+      return this.add(subscription);
+    };
+    Subscriptions.prototype.add = function add(subscription) {
+      this.subscriptions.push(subscription);
+      this.consumer.ensureActiveConnection();
+      this.notify(subscription, "initialized");
+      this.sendCommand(subscription, "subscribe");
+      return subscription;
+    };
+    Subscriptions.prototype.remove = function remove(subscription) {
+      this.forget(subscription);
+      if (!this.findAll(subscription.identifier).length) {
+        this.sendCommand(subscription, "unsubscribe");
+      }
+      return subscription;
+    };
+    Subscriptions.prototype.reject = function reject(identifier) {
+      var _this = this;
+      return this.findAll(identifier).map(function(subscription) {
+        _this.forget(subscription);
+        _this.notify(subscription, "rejected");
+        return subscription;
+      });
+    };
+    Subscriptions.prototype.forget = function forget(subscription) {
+      this.subscriptions = this.subscriptions.filter(function(s) {
+        return s !== subscription;
+      });
+      return subscription;
+    };
+    Subscriptions.prototype.findAll = function findAll(identifier) {
+      return this.subscriptions.filter(function(s) {
+        return s.identifier === identifier;
+      });
+    };
+    Subscriptions.prototype.reload = function reload() {
+      var _this2 = this;
+      return this.subscriptions.map(function(subscription) {
+        return _this2.sendCommand(subscription, "subscribe");
+      });
+    };
+    Subscriptions.prototype.notifyAll = function notifyAll(callbackName) {
+      var _this3 = this;
+      for (var _len = arguments.length, args = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+        args[_key - 1] = arguments[_key];
+      }
+      return this.subscriptions.map(function(subscription) {
+        return _this3.notify.apply(_this3, [ subscription, callbackName ].concat(args));
+      });
+    };
+    Subscriptions.prototype.notify = function notify(subscription, callbackName) {
+      for (var _len2 = arguments.length, args = Array(_len2 > 2 ? _len2 - 2 : 0), _key2 = 2; _key2 < _len2; _key2++) {
+        args[_key2 - 2] = arguments[_key2];
+      }
+      var subscriptions = void 0;
+      if (typeof subscription === "string") {
+        subscriptions = this.findAll(subscription);
+      } else {
+        subscriptions = [ subscription ];
+      }
+      return subscriptions.map(function(subscription) {
+        return typeof subscription[callbackName] === "function" ? subscription[callbackName].apply(subscription, args) : undefined;
+      });
+    };
+    Subscriptions.prototype.sendCommand = function sendCommand(subscription, command) {
+      var identifier = subscription.identifier;
+      return this.consumer.send({
+        command: command,
+        identifier: identifier
+      });
+    };
+    return Subscriptions;
+  }();
+  var ActionCable = {
+    Connection: Connection,
+    ConnectionMonitor: ConnectionMonitor,
+    Consumer: Consumer,
+    INTERNAL: INTERNAL,
+    Subscription: Subscription,
+    Subscriptions: Subscriptions,
+    WebSocket: window.WebSocket,
+    logger: window.console,
+    createConsumer: function createConsumer(url) {
+      if (url == null) {
+        var urlConfig = this.getConfig("url");
+        url = urlConfig ? urlConfig : this.INTERNAL.default_mount_path;
+      }
+      return new Consumer(this.createWebSocketURL(url));
+    },
+    getConfig: function getConfig(name) {
+      var element = document.head.querySelector("meta[name='action-cable-" + name + "']");
+      return element ? element.getAttribute("content") : undefined;
+    },
+    createWebSocketURL: function createWebSocketURL(url) {
+      if (url && !/^wss?:/i.test(url)) {
+        var a = document.createElement("a");
+        a.href = url;
+        a.href = a.href;
+        a.protocol = a.protocol.replace("http", "ws");
+        return a.href;
+      } else {
+        return url;
+      }
+    },
+    startDebugging: function startDebugging() {
+      this.debugging = true;
+    },
+    stopDebugging: function stopDebugging() {
+      this.debugging = null;
+    },
+    log: function log() {
+      if (this.debugging) {
+        var _logger;
+        for (var _len = arguments.length, messages = Array(_len), _key = 0; _key < _len; _key++) {
+          messages[_key] = arguments[_key];
+        }
+        messages.push(Date.now());
+        (_logger = this.logger).log.apply(_logger, [ "[ActionCable]" ].concat(messages));
+      }
+    }
+  };
+  return ActionCable;
+});
diff --git a/actioncable/app/javascript/action_cable/connection.js b/actioncable/app/javascript/action_cable/connection.js
index 540f597303..4ad436f2c0 100644
--- a/actioncable/app/javascript/action_cable/connection.js
+++ b/actioncable/app/javascript/action_cable/connection.js
@@ -1,158 +1,156 @@
-//= require ./connection_monitor
+import ActionCable from "./index"
+import INTERNAL from "./internal"
 
 // Encapsulate the cable connection held by the consumer. This is an internal class not intended for direct user manipulation.
 
-const {message_types, protocols} = ActionCable.INTERNAL
+const {message_types, protocols} = INTERNAL
 const supportedProtocols = protocols.slice(0, protocols.length - 1)
 
-ActionCable.Connection = (function() {
-  const indexOf = [].indexOf
+const indexOf = [].indexOf
 
-  class Connection {
-    constructor(consumer) {
-      this.open = this.open.bind(this)
-      this.consumer = consumer
-      this.subscriptions = this.consumer.subscriptions
-      this.monitor = new ActionCable.ConnectionMonitor(this)
-      this.disconnected = true
-    }
+class Connection {
+  constructor(consumer) {
+    this.open = this.open.bind(this)
+    this.consumer = consumer
+    this.subscriptions = this.consumer.subscriptions
+    this.monitor = new ActionCable.ConnectionMonitor(this)
+    this.disconnected = true
+  }
 
-    send(data) {
-      if (this.isOpen()) {
-        this.webSocket.send(JSON.stringify(data))
-        return true
-      } else {
-        return false
-      }
+  send(data) {
+    if (this.isOpen()) {
+      this.webSocket.send(JSON.stringify(data))
+      return true
+    } else {
+      return false
     }
+  }
 
-    open() {
-      if (this.isActive()) {
-        ActionCable.log(`Attempted to open WebSocket, but existing socket is ${this.getState()}`)
-        return false
-      } else {
-        ActionCable.log(`Opening WebSocket, current state is ${this.getState()}, subprotocols: ${protocols}`)
-        if (this.webSocket) { this.uninstallEventHandlers() }
-        this.webSocket = new ActionCable.WebSocket(this.consumer.url, protocols)
-        this.installEventHandlers()
-        this.monitor.start()
-        return true
-      }
+  open() {
+    if (this.isActive()) {
+      ActionCable.log(`Attempted to open WebSocket, but existing socket is ${this.getState()}`)
+      return false
+    } else {
+      ActionCable.log(`Opening WebSocket, current state is ${this.getState()}, subprotocols: ${protocols}`)
+      if (this.webSocket) { this.uninstallEventHandlers() }
+      this.webSocket = new ActionCable.WebSocket(this.consumer.url, protocols)
+      this.installEventHandlers()
+      this.monitor.start()
+      return true
     }
+  }
 
-    close({allowReconnect} = {allowReconnect: true}) {
-      if (!allowReconnect) { this.monitor.stop() }
-      if (this.isActive()) { return (this.webSocket ? this.webSocket.close() : undefined) }
-    }
+  close({allowReconnect} = {allowReconnect: true}) {
+    if (!allowReconnect) { this.monitor.stop() }
+    if (this.isActive()) { return (this.webSocket ? this.webSocket.close() : undefined) }
+  }
 
-    reopen() {
-      ActionCable.log(`Reopening WebSocket, current state is ${this.getState()}`)
-      if (this.isActive()) {
-        try {
-          return this.close()
-        } catch (error) {
-          ActionCable.log("Failed to reopen WebSocket", error)
-        }
-        finally {
-          ActionCable.log(`Reopening WebSocket in ${this.constructor.reopenDelay}ms`)
-          setTimeout(this.open, this.constructor.reopenDelay)
-        }
-      } else {
-        return this.open()
+  reopen() {
+    ActionCable.log(`Reopening WebSocket, current state is ${this.getState()}`)
+    if (this.isActive()) {
+      try {
+        return this.close()
+      } catch (error) {
+        ActionCable.log("Failed to reopen WebSocket", error)
       }
+      finally {
+        ActionCable.log(`Reopening WebSocket in ${this.constructor.reopenDelay}ms`)
+        setTimeout(this.open, this.constructor.reopenDelay)
+      }
+    } else {
+      return this.open()
     }
+  }
 
-    getProtocol() {
-      return (this.webSocket ? this.webSocket.protocol : undefined)
-    }
+  getProtocol() {
+    return (this.webSocket ? this.webSocket.protocol : undefined)
+  }
 
-    isOpen() {
-      return this.isState("open")
-    }
+  isOpen() {
+    return this.isState("open")
+  }
 
-    isActive() {
-      return this.isState("open", "connecting")
-    }
+  isActive() {
+    return this.isState("open", "connecting")
+  }
 
-    // Private
+  // Private
 
-    isProtocolSupported() {
-      return indexOf.call(supportedProtocols, this.getProtocol()) >= 0
-    }
+  isProtocolSupported() {
+    return indexOf.call(supportedProtocols, this.getProtocol()) >= 0
+  }
 
-    isState(...states) {
-      return indexOf.call(states, this.getState()) >= 0
-    }
+  isState(...states) {
+    return indexOf.call(states, this.getState()) >= 0
+  }
 
-    getState() {
-      if (this.webSocket) {
-        for (let state in WebSocket) {
-          if (WebSocket[state] === this.webSocket.readyState) {
-            return state.toLowerCase()
-          }
+  getState() {
+    if (this.webSocket) {
+      for (let state in WebSocket) {
+        if (WebSocket[state] === this.webSocket.readyState) {
+          return state.toLowerCase()
         }
       }
-      return null
     }
+    return null
+  }
 
-    installEventHandlers() {
-      for (let eventName in this.events) {
-        const handler = this.events[eventName].bind(this)
-        this.webSocket[`on${eventName}`] = handler
-      }
+  installEventHandlers() {
+    for (let eventName in this.events) {
+      const handler = this.events[eventName].bind(this)
+      this.webSocket[`on${eventName}`] = handler
     }
+  }
 
-    uninstallEventHandlers() {
-      for (let eventName in this.events) {
-        this.webSocket[`on${eventName}`] = function() {}
-      }
+  uninstallEventHandlers() {
+    for (let eventName in this.events) {
+      this.webSocket[`on${eventName}`] = function() {}
     }
-
   }
 
-  Connection.reopenDelay = 500
-
-  Connection.prototype.events = {
-    message(event) {
-      if (!this.isProtocolSupported()) { return }
-      const {identifier, message, type} = JSON.parse(event.data)
-      switch (type) {
-        case message_types.welcome:
-          this.monitor.recordConnect()
-          return this.subscriptions.reload()
-        case message_types.ping:
-          return this.monitor.recordPing()
-        case message_types.confirmation:
-          return this.subscriptions.notify(identifier, "connected")
-        case message_types.rejection:
-          return this.subscriptions.reject(identifier)
-        default:
-          return this.subscriptions.notify(identifier, "received", message)
-      }
-    },
-
-    open() {
-      ActionCable.log(`WebSocket onopen event, using '${this.getProtocol()}' subprotocol`)
-      this.disconnected = false
-      if (!this.isProtocolSupported()) {
-        ActionCable.log("Protocol is unsupported. Stopping monitor and disconnecting.")
-        return this.close({allowReconnect: false})
-      }
-    },
-
-    close(event) {
-      ActionCable.log("WebSocket onclose event")
-      if (this.disconnected) { return }
-      this.disconnected = true
-      this.monitor.recordDisconnect()
-      return this.subscriptions.notifyAll("disconnected", {willAttemptReconnect: this.monitor.isRunning()})
-    },
-
-    error() {
-      ActionCable.log("WebSocket onerror event")
+}
+
+Connection.reopenDelay = 500
+
+Connection.prototype.events = {
+  message(event) {
+    if (!this.isProtocolSupported()) { return }
+    const {identifier, message, type} = JSON.parse(event.data)
+    switch (type) {
+      case message_types.welcome:
+        this.monitor.recordConnect()
+        return this.subscriptions.reload()
+      case message_types.ping:
+        return this.monitor.recordPing()
+      case message_types.confirmation:
+        return this.subscriptions.notify(identifier, "connected")
+      case message_types.rejection:
+        return this.subscriptions.reject(identifier)
+      default:
+        return this.subscriptions.notify(identifier, "received", message)
+    }
+  },
+
+  open() {
+    ActionCable.log(`WebSocket onopen event, using '${this.getProtocol()}' subprotocol`)
+    this.disconnected = false
+    if (!this.isProtocolSupported()) {
+      ActionCable.log("Protocol is unsupported. Stopping monitor and disconnecting.")
+      return this.close({allowReconnect: false})
     }
+  },
+
+  close(event) {
+    ActionCable.log("WebSocket onclose event")
+    if (this.disconnected) { return }
+    this.disconnected = true
+    this.monitor.recordDisconnect()
+    return this.subscriptions.notifyAll("disconnected", {willAttemptReconnect: this.monitor.isRunning()})
+  },
+
+  error() {
+    ActionCable.log("WebSocket onerror event")
   }
+}
 
-  return Connection
-
-})()
+export default Connection
diff --git a/actioncable/app/javascript/action_cable/connection_monitor.js b/actioncable/app/javascript/action_cable/connection_monitor.js
index 4d2db5b4ae..8d6ac1f682 100644
--- a/actioncable/app/javascript/action_cable/connection_monitor.js
+++ b/actioncable/app/javascript/action_cable/connection_monitor.js
@@ -1,125 +1,125 @@
+import ActionCable from "./index"
+
 // Responsible for ensuring the cable connection is in good health by validating the heartbeat pings sent from the server, and attempting
 // revival reconnections if things go astray. Internal class, not intended for direct user manipulation.
-ActionCable.ConnectionMonitor = (function() {
-  const now = () => new Date().getTime()
 
-  const secondsSince = time => (now() - time) / 1000
+const now = () => new Date().getTime()
 
-  const clamp = (number, min, max) => Math.max(min, Math.min(max, number))
+const secondsSince = time => (now() - time) / 1000
 
-  class ConnectionMonitor {
-    constructor(connection) {
-      this.visibilityDidChange = this.visibilityDidChange.bind(this)
-      this.connection = connection
-      this.reconnectAttempts = 0
-    }
+const clamp = (number, min, max) => Math.max(min, Math.min(max, number))
 
-    start() {
-      if (!this.isRunning()) {
-        this.startedAt = now()
-        delete this.stoppedAt
-        this.startPolling()
-        document.addEventListener("visibilitychange", this.visibilityDidChange)
-        ActionCable.log(`ConnectionMonitor started. pollInterval = ${this.getPollInterval()} ms`)
-      }
-    }
+class ConnectionMonitor {
+  constructor(connection) {
+    this.visibilityDidChange = this.visibilityDidChange.bind(this)
+    this.connection = connection
+    this.reconnectAttempts = 0
+  }
 
-    stop() {
-      if (this.isRunning()) {
-        this.stoppedAt = now()
-        this.stopPolling()
-        document.removeEventListener("visibilitychange", this.visibilityDidChange)
-        ActionCable.log("ConnectionMonitor stopped")
-      }
+  start() {
+    if (!this.isRunning()) {
+      this.startedAt = now()
+      delete this.stoppedAt
+      this.startPolling()
+      document.addEventListener("visibilitychange", this.visibilityDidChange)
+      ActionCable.log(`ConnectionMonitor started. pollInterval = ${this.getPollInterval()} ms`)
     }
+  }
 
-    isRunning() {
-      return this.startedAt && !this.stoppedAt
+  stop() {
+    if (this.isRunning()) {
+      this.stoppedAt = now()
+      this.stopPolling()
+      document.removeEventListener("visibilitychange", this.visibilityDidChange)
+      ActionCable.log("ConnectionMonitor stopped")
     }
+  }
 
-    recordPing() {
-      this.pingedAt = now()
-    }
+  isRunning() {
+    return this.startedAt && !this.stoppedAt
+  }
 
-    recordConnect() {
-      this.reconnectAttempts = 0
-      this.recordPing()
-      delete this.disconnectedAt
-      ActionCable.log("ConnectionMonitor recorded connect")
-    }
+  recordPing() {
+    this.pingedAt = now()
+  }
 
-    recordDisconnect() {
-      this.disconnectedAt = now()
-      ActionCable.log("ConnectionMonitor recorded disconnect")
-    }
+  recordConnect() {
+    this.reconnectAttempts = 0
+    this.recordPing()
+    delete this.disconnectedAt
+    ActionCable.log("ConnectionMonitor recorded connect")
+  }
 
-    // Private
+  recordDisconnect() {
+    this.disconnectedAt = now()
+    ActionCable.log("ConnectionMonitor recorded disconnect")
+  }
 
-    startPolling() {
-      this.stopPolling()
-      this.poll()
-    }
+  // Private
 
-    stopPolling() {
-      clearTimeout(this.pollTimeout)
-    }
+  startPolling() {
+    this.stopPolling()
+    this.poll()
+  }
 
-    poll() {
-      this.pollTimeout = setTimeout(() => {
-        this.reconnectIfStale()
-        this.poll()
-      }
-      , this.getPollInterval())
-    }
+  stopPolling() {
+    clearTimeout(this.pollTimeout)
+  }
 
-    getPollInterval() {
-      const {min, max} = this.constructor.pollInterval
-      const interval = 5 * Math.log(this.reconnectAttempts + 1)
-      return Math.round(clamp(interval, min, max) * 1000)
+  poll() {
+    this.pollTimeout = setTimeout(() => {
+      this.reconnectIfStale()
+      this.poll()
     }
+    , this.getPollInterval())
+  }
 
-    reconnectIfStale() {
-      if (this.connectionIsStale()) {
-        ActionCable.log(`ConnectionMonitor detected stale connection. reconnectAttempts = ${this.reconnectAttempts}, pollInterval = ${this.getPollInterval()} ms, time disconnected = ${secondsSince(this.disconnectedAt)} s, stale threshold = ${this.constructor.staleThreshold} s`)
-        this.reconnectAttempts++
-        if (this.disconnectedRecently()) {
-          ActionCable.log("ConnectionMonitor skipping reopening recent disconnect")
-        } else {
-          ActionCable.log("ConnectionMonitor reopening")
-          this.connection.reopen()
-        }
+  getPollInterval() {
+    const {min, max} = this.constructor.pollInterval
+    const interval = 5 * Math.log(this.reconnectAttempts + 1)
+    return Math.round(clamp(interval, min, max) * 1000)
+  }
+
+  reconnectIfStale() {
+    if (this.connectionIsStale()) {
+      ActionCable.log(`ConnectionMonitor detected stale connection. reconnectAttempts = ${this.reconnectAttempts}, pollInterval = ${this.getPollInterval()} ms, time disconnected = ${secondsSince(this.disconnectedAt)} s, stale threshold = ${this.constructor.staleThreshold} s`)
+      this.reconnectAttempts++
+      if (this.disconnectedRecently()) {
+        ActionCable.log("ConnectionMonitor skipping reopening recent disconnect")
+      } else {
+        ActionCable.log("ConnectionMonitor reopening")
+        this.connection.reopen()
       }
     }
+  }
 
-    connectionIsStale() {
-      return secondsSince(this.pingedAt ? this.pingedAt : this.startedAt) > this.constructor.staleThreshold
-    }
+  connectionIsStale() {
+    return secondsSince(this.pingedAt ? this.pingedAt : this.startedAt) > this.constructor.staleThreshold
+  }
 
-    disconnectedRecently() {
-      return this.disconnectedAt && (secondsSince(this.disconnectedAt) < this.constructor.staleThreshold)
-    }
+  disconnectedRecently() {
+    return this.disconnectedAt && (secondsSince(this.disconnectedAt) < this.constructor.staleThreshold)
+  }
 
-    visibilityDidChange() {
-      if (document.visibilityState === "visible") {
-        setTimeout(() => {
-          if (this.connectionIsStale() || !this.connection.isOpen()) {
-            ActionCable.log(`ConnectionMonitor reopening stale connection on visibilitychange. visbilityState = ${document.visibilityState}`)
-            this.connection.reopen()
-          }
+  visibilityDidChange() {
+    if (document.visibilityState === "visible") {
+      setTimeout(() => {
+        if (this.connectionIsStale() || !this.connection.isOpen()) {
+          ActionCable.log(`ConnectionMonitor reopening stale connection on visibilitychange. visbilityState = ${document.visibilityState}`)
+          this.connection.reopen()
         }
-        , 200)
       }
+      , 200)
     }
-
   }
 
-  ConnectionMonitor.pollInterval = {
-    min: 3,
-    max: 30
-  }
+}
 
-  ConnectionMonitor.staleThreshold = 6 // Server::Connections::BEAT_INTERVAL * 2 (missed two pings)
+ConnectionMonitor.pollInterval = {
+  min: 3,
+  max: 30
+}
 
-  return ConnectionMonitor
+ConnectionMonitor.staleThreshold = 6 // Server::Connections::BEAT_INTERVAL * 2 (missed two pings)
 
-})()
+export default ConnectionMonitor
diff --git a/actioncable/app/javascript/action_cable/consumer.js b/actioncable/app/javascript/action_cable/consumer.js
index 731e00996d..c484ceebbd 100644
--- a/actioncable/app/javascript/action_cable/consumer.js
+++ b/actioncable/app/javascript/action_cable/consumer.js
@@ -1,6 +1,4 @@
-//= require ./connection
-//= require ./subscriptions
-//= require ./subscription
+import ActionCable from "./index"
 
 // The ActionCable.Consumer establishes the connection to a server-side Ruby Connection object. Once established,
 // the ActionCable.ConnectionMonitor will ensure that its properly maintained through heartbeats and checking for stale updates.
@@ -27,7 +25,8 @@
 //
 // Any channel subscriptions which existed prior to disconnecting will
 // automatically resubscribe.
-ActionCable.Consumer = class Consumer {
+
+export default class Consumer {
   constructor(url) {
     this.url = url
     this.subscriptions = new ActionCable.Subscriptions(this)
diff --git a/actioncable/app/javascript/action_cable/index.js.erb b/actioncable/app/javascript/action_cable/index.js
index eb85eba722..eb0c4844df 100644
--- a/actioncable/app/javascript/action_cable/index.js.erb
+++ b/actioncable/app/javascript/action_cable/index.js
@@ -1,9 +1,17 @@
-//= export ActionCable
-//= require_self
-//= require ./action_cable/consumer
+import Connection from "./connection"
+import ConnectionMonitor from "./connection_monitor"
+import Consumer from "./consumer"
+import INTERNAL from "./internal"
+import Subscription from "./subscription"
+import Subscriptions from "./subscriptions"
 
-this.ActionCable = {
-  INTERNAL: <%= ActionCable::INTERNAL.to_json %>,
+export default {
+  Connection,
+  ConnectionMonitor,
+  Consumer,
+  INTERNAL,
+  Subscription,
+  Subscriptions,
   WebSocket: window.WebSocket,
   logger: window.console,
 
@@ -12,7 +20,7 @@ this.ActionCable = {
       const urlConfig = this.getConfig("url")
       url = (urlConfig ? urlConfig : this.INTERNAL.default_mount_path)
     }
-    return new ActionCable.Consumer(this.createWebSocketURL(url))
+    return new Consumer(this.createWebSocketURL(url))
   },
 
   getConfig(name) {
diff --git a/actioncable/app/javascript/action_cable/subscription.js b/actioncable/app/javascript/action_cable/subscription.js
index 95b9ff6042..7de08f93b3 100644
--- a/actioncable/app/javascript/action_cable/subscription.js
+++ b/actioncable/app/javascript/action_cable/subscription.js
@@ -55,38 +55,35 @@
 //
 // 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.
-ActionCable.Subscription = (function() {
-  const extend = function(object, properties) {
-    if (properties != null) {
-      for (let key in properties) {
-        const value = properties[key]
-        object[key] = value
-      }
-    }
-    return object
-  }
 
-  class Subscription {
-    constructor(consumer, params = {}, mixin) {
-      this.consumer = consumer
-      this.identifier = JSON.stringify(params)
-      extend(this, mixin)
+const extend = function(object, properties) {
+  if (properties != null) {
+    for (let key in properties) {
+      const value = properties[key]
+      object[key] = value
     }
+  }
+  return object
+}
 
-    // Perform a channel action with the optional data passed as an attribute
-    perform(action, data = {}) {
-      data.action = action
-      return this.send(data)
-    }
+export default class Subscription {
+  constructor(consumer, params = {}, mixin) {
+    this.consumer = consumer
+    this.identifier = JSON.stringify(params)
+    extend(this, mixin)
+  }
 
-    send(data) {
-      return this.consumer.send({command: "message", identifier: this.identifier, data: JSON.stringify(data)})
-    }
+  // Perform a channel action with the optional data passed as an attribute
+  perform(action, data = {}) {
+    data.action = action
+    return this.send(data)
+  }
 
-    unsubscribe() {
-      return this.consumer.subscriptions.remove(this)
-    }
+  send(data) {
+    return this.consumer.send({command: "message", identifier: this.identifier, data: JSON.stringify(data)})
   }
 
-  return Subscription
-})()
+  unsubscribe() {
+    return this.consumer.subscriptions.remove(this)
+  }
+}
diff --git a/actioncable/app/javascript/action_cable/subscriptions.js b/actioncable/app/javascript/action_cable/subscriptions.js
index 65bdcc4ece..712ff50d28 100644
--- a/actioncable/app/javascript/action_cable/subscriptions.js
+++ b/actioncable/app/javascript/action_cable/subscriptions.js
@@ -1,3 +1,5 @@
+import ActionCable from "./index"
+
 // Collection class for creating (and internally managing) channel subscriptions. The only method intended to be triggered by the user
 // us ActionCable.Subscriptions#create, and it should be called through the consumer like so:
 //
@@ -6,7 +8,8 @@
 //   App.appearance = App.cable.subscriptions.create("AppearanceChannel")
 //
 // For more details on how you'd configure an actual channel subscription, see ActionCable.Subscription.
-ActionCable.Subscriptions = class Subscriptions {
+
+export default class Subscriptions {
   constructor(consumer) {
     this.consumer = consumer
     this.subscriptions = []