关于EventEmitter的用法

EventEmitter的基本用法:

 var EventEmitter = require("events").EventEmitter;
 var ee = new EventEmitter();
 ee.on("someEvent", function () {
     console.log("event has occured");
 });
 
 ee.emit("someEvent");

emit方法可以触发多个同样的事件，比如我们的页面中绑定了多个同样的someEven事件。

ee.on("someEvent", function () { console.log("event 1"); });
ee.on("someEvent", function () { console.log("event 2"); });
ee.on("someEvent", function () { console.log("event 3"); });
ee.on("someEvent", function () { console.log("event 4"); });
ee.on("someEvent", function () { console.log("event 5"); });
ee.on("someEvent", function () { console.log("event 6"); });
ee.on("someEvent", function () { console.log("event 7"); });
ee.on("someEvent", function () { console.log("event 8"); });
ee.on("someEvent", function () { console.log("event 9"); });
ee.on("someEvent", function () { console.log("event 10"); });
ee.on("someEvent", function () { console.log("event 11"); });
 
ee.emit("someEvent");

上面绑定的11个someEvent事件都会触发，但是控制台会有一条警告，因为事件对象默认监听的事件数量是10个，我们可以通过代码设置改变这个数值，例如：

 ee.setMaxListeners(20);

事件对象还有其他方法：

1，once()监听一次

2，removeListener , removeAllListeners() 移除监听事件/移除所有监听的事件

EventEmitter的高级用法:作为父类被其他类继承

比如在UserList.js文件中有UserList类

 var util         = require("util");
 var EventEmitter = require("events").EventEmitter;
 
 var id = 1;
 var database = {
     users: [
         { id: id++, name: "Joe Smith",  occupation: "developer"    },
         { id: id++, name: "Jane Doe",   occupation: "data analyst" },
         { id: id++, name: "John Henry", occupation: "designer"     }
     ]
 };
 
 util.inherits(UserList, EventEmitter);
 /*或者这样
 function UserList () {
     EventEmitter.call(this);
 }*/
 
 UserList.prototype.save = function (obj) {
     obj.id = id++;
     database.users.push(obj);
     this.emit("saved-user", obj);
 };
 
 UserList.prototype.all = function () {
     return database.users;
 };
 
 module.exports = UserList

现在我们可以在另外一个文件中这样写:

 var UserList = require("./userlist");
 var users = new UserList();
 
 users.on("saved-user", function (user) {
     console.log("saved: " + user.name + " (" + user.id + ")");
 });
 
 users.save({ name: "Jane Doe", occupation: "manager" });
 users.save({ name: "John Jacob", occupation: "developer" });

 //输出结果
 saved: Jane Doe (4)
 saved: John Jacob (5)