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