prototype
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype
Object.prototype 属性表示 Object 的原型对象。
prototype.__proto__
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/proto
Object.prototype 的 __proto__ 属性是一个访问器属性（一个getter函数和一个setter函数）, 暴露了通过它访问的对象的内部[[Prototype]] (一个对象或 null)。
prototype.constructor
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor
返回创建实例对象的 Object 构造函数的引用。注意，此属性的值是对函数本身的引用，而不是一个包含函数名称的字符串。对原始类型来说，如1，true和"test"，该值只可读。
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script>
// Person
var Person = function(name) {
this.name = name;
this.canTalk = true;
};
Person.prototype.greet = function() {
if (this.canTalk) {
console.log('Hi, I am ' + this.name);
}
};
// Employee
var Employee = function(name, title) {
Person.call(this, name);
this.title = title;
};
Employee.prototype = Object.create(Person.prototype);
Employee.prototype.constructor = Employee;
Employee.prototype.greet = function() {
if (this.canTalk) {
console.log('Hi, I am ' + this.name + ', the ' + this.title);
}
};
// instantiation
var joe = new Person('Joe');
var bob = new Employee('Bob', 'Builder');
// call function
joe.greet();
bob.greet();
// 直接打印
console.log(Person, Employee, joe , bob)
// prototype：当前对象的原型对象
console.log(Person.prototype, Employee.prototype, joe.prototype, bob.prototype)
// constructor：返回当前对象构造函数的引用
console.log(Person.constructor, Employee.constructor, joe.constructor , bob.constructor)
// __proto__：返回当前对象构造函数的原型
console.log(Person.__proto__, Employee.__proto__, joe.__proto__, bob.__proto__)
console.log(Person.constructor.prototype, Employee.constructor.prototype, joe.constructor.prototype, bob.constructor.prototype)
</script>
<script>
</script>
</body>
</html>