prototype

每个函数都有一个属性叫做prototype

这个prototype的属性值是一个对象（属性的集合，再次强调！），默认的只有一个叫做constructor的属性，指向这个函数本身

function C(){}
let o = new C()
console.log(typeof C)//function
console.log(typeof C.prototype)//object
console.log(typeof C.prototype.constructor)//Function

console.log(typeof o)//object
console.log(o.constructor)//[Function: C]
console.log(typeof o.constructor)//function

function Fn() { }
Fn.prototype.name = '王福朋';
Fn.prototype.getYear = function () {
    return 1988;
};
console.log(Fn.prototype)//{ name: '王福朋', getYear: [Function (anonymous)] }

function Fn() { }
Fn.prototype.name = '王福朋';
Fn.prototype.getYear = function () {
    return 1988;
};

var fn = new Fn();
console.log(fn.name);//王福朋
console.log(fn.getYear());//1988

let op = new Fn()
console.log(op.name)//王福朋
console.log(op.getYear());//1988

Fn是一个函数，fn对象是从Fn函数new出来的，这样fn对象就可以调用Fn.prototype中的属性。

每个对象都有一个隐藏的属性——“proto”，这个属性引用了创建这个对象的函数的prototype。即：fn.__proto__ === Fn.prototype

在看完《函数和对象的关系》，理解所有对象都是由函数创建的后，进一步深化理解了prototype和constructor的关系

console.log(typeof Object.prototype);//object
console.log(typeof Object.prototype.constructor);//function

let obj = new Object()
console.log(obj.constructor);//[Function: Object]

function fn(){}
let a = new fn()
console.log(fn.prototype);//{}
console.log(a.constructor);//[Function: fn]
fn.prototype = Object
console.log(typeof fn.prototype);//function
console.log(a.constructor);//[Function: fn]
console.log(a.constructor.prototype);//[Function: Object]
console.log(a.constructor.prototype.constructor);//[Function: Function]