node语法-事件(event)

class EventEmitter {
    // 构造函数
	constructor() {
		this._events = {
			/*
			'click':[
				function(){},
				function(){},
				function(){}
			]*/
		}
		/*
		for(var i=0;i<this._events.click.length;i++){
			this._events.click[i]();
		}*/
	}
	// 发出事件
	emit(type) {
		var funs = this._events[type];
		for(var i=0;funs && i<funs.length;i++) {
			// { '0': 'userAdded', '1': 'colin', '2': 'password' } length 3
			console.log(arguments);
			// 将一个有length属性的对象转成一个数组
			var arg = Array.prototype.slice.call(arguments);
			// [ 'userAdded', 'colin', 'password' ]
			console.log(arg); 
			funs[i].apply(this,(arg.slice(1)));
		}
	}
	// 移除监听
	removeListener(type) {
		delete this._events[type];
	}	
	// 添加监听
	addListener(type, fun) {
		this._events = this._events || {};
		if(!this._events[type]) {
			this._events[type] = [];
		}
		this._events[type].push(fun);
	}
	// 一次监听
	once(type, fun) {
		this.addListener(type, _onceWrap(this, type, fun));
	}
}


function _onceWrap(target, type, listener) {
	var fired = false;
	function g() {
		target.removeListener(type, g); // 绑定的函数去除
		if(!fired) {
			fired = true;
			listener.apply(target,arguments);
		}
	}
	return g;
}

// 完全一样on 可能是为了兼容老版本
EventEmitter.prototype.on = EventEmitter.prototype.addListener; 
EventEmitter.EventEmitter = EventEmitter;
module.exports = exports = EventEmitter;

var events = require('./customEvent');
var emitter = new events.EventEmitter();
var username = "colin";
var password = "password";
emitter.addListener('userAdded', function(user, pwd) {
	console.log(user, pwd);
})
emitter.emit("userAdded", username, password);

emitter.once("foo", function(){
	console.log("in foo handerler");
});
emitter.emit("foo");
emitter.emit("foo");
emitter.emit("foo");

var events = require("events");
var emitter = new events.EventEmitter();

var f = function(){}
emitter.on("newListener", function(eventName,listener) {
	console.log("" + eventName + "",listener === f);
})
emitter.on("foo",f); // foo true

// 下面是第二个检测实例
var events = require("events");
var emitter = new events.EventEmitter();
emitter.on("newListener", function(date) {
	console.log(date); 
});
// 时间
emitter.emit("newListener", new Date); 
// foo 
emitter.on("foo", function(){});

var EventEmitter = require("./customEvent").EventEmitter;
// 引入util来实现继承
var util = require("util");
function UserEventEmitter() {
	this.addUser = function(username, password) {
		this.emit("userAdded", username, password);
	};
};

// 继承 第一参数是子类 第二参数是父类
util.inherits(UserEventEmitter, EventEmitter);

// 使用
var user = new UserEventEmitter();
var username = "colin1";
var password = "password";
user.on("userAdded", function(username,password){
	console.log("Added user " + username);
});
//user.addUser(username,password);
//user.emit("userAdded", username, password);

// true; user是不是EventEmitter的实例
console.log(user instanceof EventEmitter)

emitter.setMaxListeners(2);
emitter.on("aa", function(date){
	console.log("a");
});
emitter.on("aa", function(date){
	console.log("a");
});
emitter.on("aa",function(date){
 	console.log("a");
})

emitter.prependListener("aa", function(date){
	console.log('a');
});
emitter.prependListener("aa", function(date){
	console.log('b');
});
// 输出  b a
emitter.emit('aa');