1 files changed, 193 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/event/core.js b/toolkit/jetpack/sdk/event/core.js
new file mode 100644
index 000000000..c16dd2df5
--- /dev/null
+++ b/toolkit/jetpack/sdk/event/core.js
@@ -0,0 +1,193 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+module.metadata = {
+  "stability": "unstable"
+};
+
+const UNCAUGHT_ERROR = 'An error event was emitted for which there was no listener.';
+const BAD_LISTENER = 'The event listener must be a function.';
+
+const { ns } = require('../core/namespace');
+
+const event = ns();
+
+const EVENT_TYPE_PATTERN = /^on([A-Z]\w+$)/;
+exports.EVENT_TYPE_PATTERN = EVENT_TYPE_PATTERN;
+
+// Utility function to access given event `target` object's event listeners for
+// the specific event `type`. If listeners for this type does not exists they
+// will be created.
+const observers = function observers(target, type) {
+  if (!target) throw TypeError("Event target must be an object");
+  let listeners = event(target);
+  return type in listeners ? listeners[type] : listeners[type] = [];
+};
+
+/**
+ * Registers an event `listener` that is called every time events of
+ * specified `type` is emitted on the given event `target`.
+ * @param {Object} target
+ *    Event target object.
+ * @param {String} type
+ *    The type of event.
+ * @param {Function} listener
+ *    The listener function that processes the event.
+ */
+function on(target, type, listener) {
+  if (typeof(listener) !== 'function')
+    throw new Error(BAD_LISTENER);
+
+  let listeners = observers(target, type);
+  if (!~listeners.indexOf(listener))
+    listeners.push(listener);
+}
+exports.on = on;
+
+
+var onceWeakMap = new WeakMap();
+
+
+/**
+ * Registers an event `listener` that is called only the next time an event
+ * of the specified `type` is emitted on the given event `target`.
+ * @param {Object} target
+ *    Event target object.
+ * @param {String} type
+ *    The type of the event.
+ * @param {Function} listener
+ *    The listener function that processes the event.
+ */
+function once(target, type, listener) {
+  let replacement = function observer(...args) {
+    off(target, type, observer);
+    onceWeakMap.delete(listener);
+    listener.apply(target, args);
+  };
+  onceWeakMap.set(listener, replacement);
+  on(target, type, replacement);
+}
+exports.once = once;
+
+/**
+ * Execute each of the listeners in order with the supplied arguments.
+ * All the exceptions that are thrown by listeners during the emit
+ * are caught and can be handled by listeners of 'error' event. Thrown
+ * exceptions are passed as an argument to an 'error' event listener.
+ * If no 'error' listener is registered exception will be logged into an
+ * error console.
+ * @param {Object} target
+ *    Event target object.
+ * @param {String} type
+ *    The type of event.
+ * @params {Object|Number|String|Boolean} args
+ *    Arguments that will be passed to listeners.
+ */
+function emit (target, type, ...args) {
+  emitOnObject(target, type, target, ...args);
+}
+exports.emit = emit;
+
+/**
+ * A variant of emit that allows setting the this property for event listeners
+ */
+function emitOnObject(target, type, thisArg, ...args) {
+  let all = observers(target, '*').length;
+  let state = observers(target, type);
+  let listeners = state.slice();
+  let count = listeners.length;
+  let index = 0;
+
+  // If error event and there are no handlers (explicit or catch-all)
+  // then print error message to the console.
+  if (count === 0 && type === 'error' && all === 0)
+    console.exception(args[0]);
+  while (index < count) {
+    try {
+      let listener = listeners[index];
+      // Dispatch only if listener is still registered.
+      if (~state.indexOf(listener))
+        listener.apply(thisArg, args);
+    }
+    catch (error) {
+      // If exception is not thrown by a error listener and error listener is
+      // registered emit `error` event. Otherwise dump exception to the console.
+      if (type !== 'error') emit(target, 'error', error);
+      else console.exception(error);
+    }
+    index++;
+  }
+   // Also emit on `"*"` so that one could listen for all events.
+  if (type !== '*') emit(target, '*', type, ...args);
+}
+exports.emitOnObject = emitOnObject;
+
+/**
+ * Removes an event `listener` for the given event `type` on the given event
+ * `target`. If no `listener` is passed removes all listeners of the given
+ * `type`. If `type` is not passed removes all the listeners of the given
+ * event `target`.
+ * @param {Object} target
+ *    The event target object.
+ * @param {String} type
+ *    The type of event.
+ * @param {Function} listener
+ *    The listener function that processes the event.
+ */
+function off(target, type, listener) {
+  let length = arguments.length;
+  if (length === 3) {
+    if (onceWeakMap.has(listener)) {
+      listener = onceWeakMap.get(listener);
+      onceWeakMap.delete(listener);
+    }
+
+    let listeners = observers(target, type);
+    let index = listeners.indexOf(listener);
+    if (~index)
+      listeners.splice(index, 1);
+  }
+  else if (length === 2) {
+    observers(target, type).splice(0);
+  }
+  else if (length === 1) {
+    let listeners = event(target);
+    Object.keys(listeners).forEach(type => delete listeners[type]);
+  }
+}
+exports.off = off;
+
+/**
+ * Returns a number of event listeners registered for the given event `type`
+ * on the given event `target`.
+ */
+function count(target, type) {
+  return observers(target, type).length;
+}
+exports.count = count;
+
+/**
+ * Registers listeners on the given event `target` from the given `listeners`
+ * dictionary. Iterates over the listeners and if property name matches name
+ * pattern `onEventType` and property is a function, then registers it as
+ * an `eventType` listener on `target`.
+ *
+ * @param {Object} target
+ *    The type of event.
+ * @param {Object} listeners
+ *    Dictionary of listeners.
+ */
+function setListeners(target, listeners) {
+  Object.keys(listeners || {}).forEach(key => {
+    let match = EVENT_TYPE_PATTERN.exec(key);
+    let type = match && match[1].toLowerCase();
+    if (!type) return;
+
+    let listener = listeners[key];
+    if (typeof(listener) === 'function')
+      on(target, type, listener);
+  });
+}
+exports.setListeners = setListeners;