Merge pull request #58 from Automattic/refactor/events

refactor: events module

lib/events.js

@@ -1,13 +1,22 @@
 'use strict';
 
 // Modules.
-const _ = require('lodash');
-const EventEmitter = require('events').EventEmitter;
+const {EventEmitter} = require('events');
 const Log = require('./logger');
 const Promise = require('./promise');
 
-/*
+/**
+ * @typedef {Object} Listener
+ * @property {string} name The name of the event
+ * @property {number} priority The priority the event should run in.
+ * @property {Function} fn The function to call. Should get the args specified in the corresponding `emit` declaration.
+ */
+
+/**
  * Creates a new Events instance.
+ *
+ * @property {Log} log The log instance.
+ * @property {Listener[]} _listeners The listeners for this event emitter.
  */
 class AsyncEvents extends EventEmitter {
   constructor(log = new Log()) {
@@ -25,10 +34,10 @@ class AsyncEvents extends EventEmitter {
    *
    * @since 3.0.0
    * @alias lando.events.on
-   * @param {String} name The name of the event
-   * @param {Integer} [priority=5] The priority the event should run in.
-   * @param {Function} fn The function to call. Should get the args specified in the corresponding `emit` declaration.
-   * @return {Promise} A Promise
+   * @param {string} name The name of the event
+   * @param {number|Function} [priority] If a number, the priority the event should run in; if a function, the function to call.
+   * @param {Function} [fn] The function to call. Should get the args specified in the corresponding `emit` declaration.
+   * @return {this}
    * @example
    * // Print out all our apps as they get instantiated and do it before other `post-instantiate-app` events
    * lando.events.on('post-instantiate-app', 1, app => {
@@ -43,17 +52,16 @@ class AsyncEvents extends EventEmitter {
    */
   on(name, priority, fn) {
     // Handle no priority
-    // @todo: is there a way to get this working nicely via es6?
-    if (_.isUndefined(fn) && _.isFunction(priority)) {
+    if (typeof fn === 'undefined' && typeof priority === 'function') {
       fn = priority;
       priority = 5;
     }
     // Store
     this._listeners.push({name, priority, fn});
     // Log
     this.log.silly('loading event %s priority %s', name, priority);
-    // Call originl on method.
-    return this.__on(name, fn);
+    // Call original on method.
+    return super.on(name, fn);
   };
 
   /**
@@ -63,58 +71,32 @@ class AsyncEvents extends EventEmitter {
    *
    * @since 3.0.0
    * @alias lando.events.emit
-   * @param {String} name The name of the event
-   * @param {...Any} [args] Options args to pass.
-   * @return {Promise} A Promise
+   * @param {string} name The name of the event
+   * @param {...any} args Options args to pass.
+   * @return {Promise<boolean>} A Promise
    * @example
    * // Emits a global event with a config arg
    * return lando.events.emit('wolf359', config);
    *
    * // Emits an app event with a config arg
    * return app.events.emit('sector001', config);
    */
-  emit(...args) {
-    /*
-     * Helper function that will always return a promise even if function is
-     * synchronous and doesn't return a promise.
-     * @todo: this is very old kbox code, can we update it a bit?
-     */
-    const handle = (...args) => {
-      const fn = args.shift();
-      const result = fn.apply(this, args);
-      return Promise.resolve(result);
-    };
-    // Save for later
-    const self = this;
-    // Grab name of event from first argument.
-    const name = args.shift();
-
-    // Grab priority sorted listeners for this event
-    const evnts = _(this._listeners)
-      // Filter by name
+  emit(name, ...args) {
+    const fns = this._listeners
       .filter(listener => listener.name === name)
-      // Sort by priority
-      .sortBy('priority')
-      // Return value
-      .value();
-
-    // Map to array of func
-    const fns = _.map(evnts, evnt => evnt.fn);
+      .sort((a, b) => a.priority - b.priority)
+      .map(evnt => evnt.fn);
 
     // Log non engine events so we can keep things quiet
-    if (!_.includes(name, '-engine-')) {
+    if (!name.includes('-engine-')) {
       this.log.debug('emitting event %s', name);
       this.log.silly('event %s has %s listeners', name, fns.length);
     }
 
     // Make listener functions to a promise in series.
     return Promise.each(fns, fn => {
-      // Clone function arguments.
-      const fnArgs = args.slice();
-      // Add listener function to front of arguments.
-      fnArgs.unshift(fn);
       // Apply function that calls the listener function and returns a promise.
-      return handle.apply(self, fnArgs);
+      return fn(...args);
     })
 
     // Make sure to wait for all mappings.
@@ -125,30 +107,7 @@ class AsyncEvents extends EventEmitter {
   };
 };
 
-/*
- * Stores the original event on method.
- *
- * I don't think you want to ever really use this. Mentioned only for transparency.
- *
- * @alias lando.events.__on
- * @see https://nodejs.org/api/events.html
- */
-AsyncEvents.prototype.__on = EventEmitter.prototype.on;
-
-/*
- * Stores the original event emit method.
- *
- * I don't think you want to ever really use this. Mentioned only for transparency.
- *
- * @alias lando.events.__emit
- * @see https://nodejs.org/api/events.html
- */
-AsyncEvents.prototype.__emit = EventEmitter.prototype.emit;
-
 // Set our maxListeners to something more reasonable for lando
 AsyncEvents.prototype.setMaxListeners(64);
 
-/*
- * Return the class
- */
 module.exports = AsyncEvents;