《JavaScript应用程序设计》一一3.7创建对象

本节书摘来华章计算机出版社《JavaScript应用程序设计》一书中的第3章，第3.7节，作者：Eric Elliott 更多章节内容可以访问云栖社区“华章计算机”公众号查看。

3.7 创建对象

JavaScript中的对象一部分是通过构造函数生成的，例如：

function Car(color, direction, mph) { this.color = color || 'pink'; this.direction = direction || 0; // 0 = Straight ahead this.mph = mph || 0; this.gas = function gas(amount) { amount = amount || 10; this.mph += amount; return this; }; this.brake = function brake(amount) { amount = amount || 10; this.mph = ((this.mph - amount) < 0)? 0 : this.mph - amount; return this; }; } var myCar = new Car(); test('Constructor', function () { ok(myCar.color, 'Has a color'); equal(myCar.gas().mph, 10, '.accelerate() should add 10mph.' ); equal(myCar.brake(5).mph, 5, '.brake(5) should subtract 5mph.' ); });

使用私有变量来做数据封装：

function Car(color, direction, mph) { var isParkingBrakeOn = false; this.color = color || 'pink'; this.direction = direction || 0; // 0 = Straight ahead this.mph = mph || 0; this.gas = function gas(amount) { amount = amount || 10; this.mph += amount; return this; }; this.brake = function brake(amount) { amount = amount || 10; this.mph = ((this.mph - amount) < 0)? 0 : this.mph - amount; return this; }; this.toggleParkingBrake = function toggleParkingBrake() { isParkingBrakeOn = !isParkingBreakOn; return this; }; this.isParked = function isParked() { return isParkingBrakeOn; } } var myCar = new Car(); test('Constructor with private property.', function () { ok(myCar.color, 'Has a color'); equal(myCar.gas().mph, 10, '.accelerate() should add 10mph.' ); equal(myCar.brake(5).mph, 5, '.brake(5) should subtract 5mph.' ); ok(myCar.toggleParkingBrake().isParked(), '.toggleParkingBrake works.' ); });

对象字面量让对象构建的语法更为简单直观：

var myCar = { color: 'pink', direction: 0, mph: 0, gas: function gas(amount) { amount = amount || 10; this.mph += amount; return this; }, brake: function brake(amount) { amount = amount || 10; this.mph = ((this.mph - amount) < 0)? 0 : this.mph - amount; return this; } }; test('Object literal notation.', function () { ok(myCar.color, 'Has a color'); equal(myCar.gas().mph, 10, '.accelerate() should add 10mph.' ); equal(myCar.brake(5).mph, 5, '.brake(5) should subtract 5mph.' ); });

请注意，由于对象字面量不具备函数作用域，所以数据封装性会丢失。

相关资源：JavaScript高级程序设计