Node.js之事件监听和发送

const events = require("events");

function Account() {

    this.balance = 0;

    events.EventEmitter.call(this);

    this.deposid = function (amount) {

        this.balance += amount;

        this.emit("balanceChanged");

    };

    this.withdraw = function (amount) {

        this.balance -= amount;

        this.emit("balanceChanged");

    };

}

Account.prototype.__proto__ = events.EventEmitter.prototype;

function displayBalance() {

    console.log("Account  balance: $%d", this.balance);

}

function checkOverdraw() {

    if (this.balance < 0) {

        console.log("Account overdraw!!!");

    }

}

function checkGoal(acc, goal) {

    if (acc.balance > goal) {

        console.log("Goal archieved!!!");

    }

}

const account = new  Account();

account.on("balanceChanged", displayBalance);

account.on("balanceChanged", checkOverdraw);

account.on("balanceChanged", function () {

    checkGoal(this, 1000);

});

account.deposid(220);

account.deposid(320);

account.deposid(620);

account.withdraw(1200);

打印结果：

Account  balance: $220

Account  balance: $540

Account  balance: $1160

Goal archieved!!!

Account  balance: $-40

Account overdraw!!!