原型&继承

1

function Person(name) {
  this.name = name
}
var p2 = new Person("king")
console.log(p2.__proto__)
console.log(p2.__proto__.__proto__)
console.log(p2.__proto__.__proto__.__proto__)
console.log(p2.__proto__.__proto__.__proto__.__proto__)
console.log(p2.__proto__.__proto__.__proto__.__proto__.__proto__)
console.log(p2.constructor)
console.log(p2.prototype)
console.log(Person.constructor)
console.log(Person.prototype)
console.log(Person.prototype.constructor)
console.log(Person.prototype.__proto__)
console.log(Person.__proto__)
console.log(Function.prototype.__proto__)
console.log(Function.__proto__)
console.log(Object.__proto__)
console.log(Object.prototype.__proto__)

Person.prototype
Object.prototype
null
报错
报错
Person
undefined
Function
打印出Person.prototype这个对象里所有的方法和属性
Person
Object.prototype
Function.prototype
Object.prototype
Function.prototype
Function.prototype
null

2

function Foo() {
  getName = function () {
    console.log(1)
  }
  return this
}
 
Foo.getName = function () {
  console.log(2)
}
 
Foo.prototype.getName = function () {
  console.log(3)
}
 
var getName = function () {
  console.log(4)
}
 
function getName() {
  console.log(5)
}
 
Foo.getName()
getName()
Foo().getName()
getName()
new Foo.getName()
new Foo().getName()
new new Foo().getName()

2
4
1
1
2
3
3

3

var F = function () {}
Object.prototype.a = function () {
  console.log("a")
}
Function.prototype.b = function () {
  console.log("b")
}
var f = new F()
f.a()
f.b()
F.a()
F.b()

a
报错
a
b

4

function Foo() {
  Foo.a = function () {
    console.log(1)
  }
  this.a = function () {
    console.log(2)
  }
}
 
Foo.prototype.a = function () {
  console.log(3)
}
 
Foo.a = function () {
  console.log(4)
}
 
Foo.a()
let obj = new Foo()
obj.a()
Foo.a()

4
2
1

5

function Dog() {
  this.name = "puppy"
}
Dog.prototype.bark = () => {
  console.log("woof!woof!")
}
const dog = new Dog()
console.log(Dog.prototype.constructor === Dog && dog.constructor === Dog && dog instanceof Dog)

true

6

var A = { n: 4399 }
var B = function () {
  this.n = 9999
}
var C = function () {
  var n = 8888
}
B.prototype = A
C.prototype = A
var b = new B()
var c = new C()
A.n++
console.log(b.n)
console.log(c.n)

9999
4400

7

function A() {}
function B(a) {
  this.a = a
}
function C(a) {
  if (a) {
    this.a = a
  }
}
A.prototype.a = 1
B.prototype.a = 1
C.prototype.a = 1
 
console.log(new A().a)
console.log(new B().a)
console.log(new C(2).a)

1
undefined
2

8

function Parent() {
  this.a = 1
  this.b = [1, 2, this.a]
  this.c = { demo: 5 }
  this.show = function () {
    console.log(this.a, this.b, this.c.demo)
  }
}
 
function Child() {
  this.a = 2
  this.change = function () {
    this.b.push(this.a)
    this.a = this.b.length
    this.c.demo = this.a++
  }
}
 
Child.prototype = new Parent()
var parent = new Parent()
var child1 = new Child()
var child2 = new Child()
child1.a = 11
child2.a = 12
parent.show()
child1.show()
child2.show()
child1.change()
child2.change()
parent.show()
child1.show()
child2.show()

1 [1, 2, 1] 5
11 [1, 2, 1] 5
12 [1, 2, 1] 5
1 [1, 2, 1] 5
5 [1, 2, 1, 11, 12] 5
6 [1, 2, 1, 11, 12] 5

9

function SuperType() {
  this.property = true
}
 
SuperType.prototype.getSuperValue = function () {
  return this.property
}
 
function SubType() {
  this.subproperty = false
}
 
SubType.prototype = new SuperType()
SubType.prototype.getSubValue = function () {
  return this.subproperty
}
 
var instance = new SubType()
console.log(instance.getSuperValue())

true