| /** |
| * @fileoverview A variant of EventEmitter which does not give listeners information about each other |
| * @author Teddy Katz |
| */ |
| |
| "use strict"; |
| |
| //------------------------------------------------------------------------------ |
| // Typedefs |
| //------------------------------------------------------------------------------ |
| |
| /** |
| * An event emitter |
| * @typedef {Object} SafeEmitter |
| * @property {function(eventName: string, listenerFunc: Function): void} on Adds a listener for a given event name |
| * @property {function(eventName: string, arg1?: any, arg2?: any, arg3?: any)} emit Emits an event with a given name. |
| * This calls all the listeners that were listening for that name, with `arg1`, `arg2`, and `arg3` as arguments. |
| * @property {function(): string[]} eventNames Gets the list of event names that have registered listeners. |
| */ |
| |
| /** |
| * Creates an object which can listen for and emit events. |
| * This is similar to the EventEmitter API in Node's standard library, but it has a few differences. |
| * The goal is to allow multiple modules to attach arbitrary listeners to the same emitter, without |
| * letting the modules know about each other at all. |
| * 1. It has no special keys like `error` and `newListener`, which would allow modules to detect when |
| * another module throws an error or registers a listener. |
| * 2. It calls listener functions without any `this` value. (`EventEmitter` calls listeners with a |
| * `this` value of the emitter instance, which would give listeners access to other listeners.) |
| * @returns {SafeEmitter} An emitter |
| */ |
| module.exports = () => { |
| const listeners = Object.create(null); |
| |
| return Object.freeze({ |
| on(eventName, listener) { |
| if (eventName in listeners) { |
| listeners[eventName].push(listener); |
| } else { |
| listeners[eventName] = [listener]; |
| } |
| }, |
| emit(eventName, ...args) { |
| if (eventName in listeners) { |
| listeners[eventName].forEach(listener => listener(...args)); |
| } |
| }, |
| eventNames() { |
| return Object.keys(listeners); |
| } |
| }); |
| }; |