//练习js继承（组合继承：原型继承和构造函数继承的组合）function Polygon(length, area) {    this.length = length;    this.area = area;}Polygon.prototype = {    constructor: Polygon,    getLength: function () { console.log(this.length);console.log(" Polygon--getLength()!"); },    getArea: function () { console.log(this.area); },    sayHello: function () { console.log("Hi,I'm Polygon!");}}function Triangle(length, area) {    //继承属性    Polygon.call(this, length, area);//在子类对象上调用父类构造函数   //添加新属性   //this.a=a;}//继承方法Triangle.prototype = new Polygon();//注意：通过原型链实现继承时，不能使用对象字面量创建原型的方法，会导致重写原型链/*Triangle.prototype = {    constructor: Triangle,    getLength: function () { console.log("Triangle length is " + this.length); }，    getArea: function () { console.log("Triangle area is " + this.area); }}*/Triangle.prototype.constructor = Triangle;//设置constructor属性//重写父类方法Triangle.prototype.getLength = function () {    //Polygon.prototype.getLength.call(this);    console.log("Triangle length is " + this.length);};Triangle.prototype.getArea = function () {    console.log("Triangle area is " + this.area);};//添加新方法Triangle.prototype.sayTriangle = function () { console.log("Hi,I'm Triangle!"); };var polygon1 = new Polygon(1, 2);polygon1.getLength();polygon1.getArea();var triangle1 = new Triangle(12, 16);//调用子类重写的方法triangle1.getLength();triangle1.getArea();//调用子类的新方法triangle1.sayTriangle();//调用父类未被重写的方法triangle1.sayHello();//调用父类被重写的方法Polygon.prototype.getLength.call(triangle1);

console打印信息：

1

Polygon--getLength()!

2

Triangle length is 12

Triangle area is 16

Hi,I'm Triangle!

Hi,I'm Polygon!

12

Polygon--getLength()!