方法说明：

发射event事件，传递若干可选参数到事件监听器的参数表。

语法：

emitter.emit(event, [arg1], [arg2], [...])

接收参数：

event 事件类型

arg1 ~ argN 传递的参数(多个)

例子：

var  events = require('events');

var emitter = new events.EventEmitter();

 

emitter.on('someEvent', function(arg1, arg2){

    console.log('listener1', arg1, arg2);

})

 

emitter.on('someEvent', function(arg1, arg2){

    console.log('listener2', arg1, arg2);

})

 

emitter.emit('someEvent', 'byvoid', 1991);

源码：

EventEmitter.prototype.emit = function(type) {

  var er, handler, len, args, i, listeners;

  if (!this._events)

    this._events = {};

  // If there is no 'error' event listener then throw.

  if (type === 'error') {

    if (!this._events.error ||

        (util.isObject(this._events.error) && !this._events.error.length)) {

      er = arguments[1];

      if (this.domain) {

        if (!er) er = new TypeError('Uncaught, unspecified "error" event.');

        er.domainEmitter = this;

        er.domain = this.domain;

        er.domainThrown = false;

        this.domain.emit('error', er);

      } else if (er instanceof Error) {

        throw er; // Unhandled 'error' event

      } else {

        throw TypeError('Uncaught, unspecified "error" event.');

      }

      return false;

    }

  }

  handler = this._events[type];

  if (util.isUndefined(handler))

    return false;

  if (this.domain && this !== process)

    this.domain.enter();

  if (util.isFunction(handler)) {

    switch (arguments.length) {

      // fast cases

      case 1:

        handler.call(this);

        break;

      case 2:

        handler.call(this, arguments[1]);

        break;

      case 3:

        handler.call(this, arguments[1], arguments[2]);

        break;

      // slower

      default:

        len = arguments.length;

        args = new Array(len - 1);

        for (i = 1; i < len; i++)

          args[i - 1] = arguments[i];

        handler.apply(this, args);

    }

  } else if (util.isObject(handler)) {

    len = arguments.length;

    args = new Array(len - 1);

    for (i = 1; i < len; i++)

      args[i - 1] = arguments[i];

    listeners = handler.slice();

    len = listeners.length;

    for (i = 0; i < len; i++)

      listeners[i].apply(this, args);

  }

  if (this.domain && this !== process)

    this.domain.exit();

  return true;

};