You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
52 lines
2.1 KiB
52 lines
2.1 KiB
/** |
|
* @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); |
|
} |
|
}); |
|
};
|
|
|