Question

我不明白如何使用function(msg)...调用myEmmiter.emit .emit('someEvent', ...)如何知道论据'the event was emitted'应该传递给function(msg)...？有没有办法查看emit方法来源？

const events = require('events');
var myEmmiter = new events.EventEmitter();

myEmmiter.on('someEvent', function (msg) {
  console.log(msg);
});

myEmmiter.emit('someEvent', 'the event was emitted');

Answer 1

events模块的实现可在此处找到：https://github.com/nodejs/node/blob/master/lib/events.js

在摘要中，EventEmitter实例维护一个对象，其中键是事件名称（someEvent），值是每当生成该事件时应调用的函数数组：

this.registeredEvents = {
  someEvent : [ handler ]
};

要注册活动，请使用emitter.on()/emitter.addListener()：

on(eventName, handler) {
  if (! Array.isArray(this.registeredEvents[eventName])) {
    this.registeredEvents[eventName] = [];
  }
  this.registeredEvents[eventName].push(handler);
}

当您调用emitter.emit()时，将使用参数：

调用每个处理程序

emit(eventName, message) {
  (this.registeredEvents[eventName] || []).forEach(handler => handler(message));
}

Node.js发射器如何工作？理解传递参数

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