function Person() {
    this.name = 'sanlyshi';
    this.age = '23';
    this.eat = function () {
        console.log(this.name +' is eating!')
    }
}
Person.prototype.smell = function () {
    console.log("smell");
};
var person1 = new Person();
console.log(person1.name);   //sanlyshi
person1.eat();               
 
//sanlyshi is eating!
person1.smell();             //smell


// 每個"函式"都有一個prototype屬性，指向一個"物件"
// "物件"具有屬性__proto__，可稱為隱式原型，一個物件的隱式原型指向構造該物件的建構函式的原型
// 1
console.log(Object.prototype.__proto__ === null);   //true
// 2
console.log(Function.prototype.__proto__ === Object.prototype);   //true
// 3
console.log(Person.__proto__ === Function.prototype);   
 
//true
// 4
console.log(person1.__proto__ === Person.prototype);   //true



// "prototype物件"有一個constructor屬性，預設指向prototype物件所在的建構函式
console.log(Person.prototype.constructor === Person);   //true
console.log(Function.prototype.constructor === Function);   //true
console.log(Object.prototype.constructor === Object);   
 
//true