關於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方法可以觸發多個同樣的事件，比如我們的頁面中綁定了多個同樣的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");

上面綁定的11個someEvent事件都會觸發，但是控制台會有一條警告，因為事件對象默認監聽的事件數量是10個，我們可以通過代碼設置改變這個數值，例如：

ee.setMaxListeners(20);

事件對象還有其他方法：

1，once()監聽一次

2，removeListener , removeAllListeners() 移除監聽事件/移除所有監聽的事件

EventEmitter的高級用法:作為父類被其他類繼承

比如在UserList.js文件中有UserList類

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);
/*或者這樣
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

 

現在我們可以在另外一個文件中這樣寫:

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" });

//輸出結果
saved: Jane Doe (4)
saved: John Jacob (5)