프로토타입과 프로토타입 체인의 특성과 용도를 이해합니다.

function Person(name, age) {
  this.name = name;
  this.age = age;
}

Person.prototype.greet = function() {
  console.log('Hello, ' + this.name + '!');
};

var person1 = new Person('Alice', 20);
var person2 = new Person('Bob', 25);

console.log(person1.__proto__ === person2.__proto__);  // true

person1.greet();  // Hello, Alice!

console.log(person1.hasOwnProperty('name'));  // true，对象自身有name属性
console.log(person1.hasOwnProperty('greet'));  // false，对象自身没有greet方法

console.log(person1.__proto__.hasOwnProperty('greet'));  // true，原型对象有greet方法

person1.name = 'Eve';

console.log(person1.hasOwnProperty('name'));  // true，对象自身有name属性，不会修改原型对象的属性

function Animal(name) {
  this.name = name;
}

function Cat(name, color) {
  this.name = name;
  this.color = color;
}

Cat.prototype = new Animal();

var cat = new Cat('Tom', 'blue');

console.log(cat instanceof Cat);  // true
console.log(cat instanceof Animal);  // true

console.log(cat.hasOwnProperty('name'));  // true，对象自身有name属性
console.log(cat.hasOwnProperty('color'));  // true，对象自身有color属性

console.log(cat.__proto__ === Cat.prototype);  // true
console.log(Cat.prototype.__proto__ === Animal.prototype);  // true
console.log(Animal.prototype.__proto__ === Object.prototype);  // true，原型链的顶端是Object.prototype

function Animal(name) {
  this.name = name;
}

Animal.prototype.eat = function() {
  console.log(this.name + ' is eating.');
};

function Cat(name, color) {
  this.name = name;
  this.color = color;
}

Cat.prototype = new Animal();

var cat = new Cat('Tom', 'blue');

cat.eat();  // Tom is eating.

function Person(name, age) {
  this.name = name;
  this.age = age;
}

Person.prototype.sayHi = function() {
  console.log('Hi, I am ' + this.name);
};

var person1 = new Person('Alice', 20);
var person2 = new Person('Bob', 25);

person1.sayHi();  // Hi, I am Alice
person2.sayHi();  // Hi, I am Bob