function Star(name, age) {
            this.name = name;
            this.age = age;
            this.sing = function () {
                console.log(this.name + '会唱歌');
            }
        }

        var ht = new Star('河图', 3);

        //每一个构造函数都有prototype属性，该属性指向一个对象
        //实例化对象都会有一个属性__proto__，指向构造函数的原型对象prototype
        console.log(Star.prototype);    //constructor: ƒ Star(name, age)
        console.log(Star.prototype == ht.__proto__);    //true

        //原型对象prototype的构造函数construor指向Star构造函数
        console.log(Star.prototype.constructor == Star);   //true

        //Star原型对象prototype.__proto__指向Object原型对象prototype
        console.log(Star.prototype.__proto__ == Object.prototype);    //true

        //Object原型对象prototype的构造函数construor指向Object构造函数
        console.log(Object.prototype.constructor == Object);    //true

        //Object原型对象prototype.__proto__指向空null
        console.log(Object.prototype.__proto__);    //null