JS继承

原型链继承

function Parent () {
    this.name = 'marshall';
}

Parent.prototype.getName = function () {
    console.log(this.name);
}

function Child () {

}

Child.prototype = new Parent();

var child1 = new Child();

console.log(child1.getName()) // marshall

1. 这种继承方式中，引用类型的属性被所有实例共享
   e.g.

function Parent () {
    this.names = ['kevin', 'daisy'];
}

function Child () {

}

Child.prototype = new Parent();

var child1 = new Child();

child1.names.push('yayu');

console.log(child1.names); // ["kevin", "daisy", "yayu"]

var child2 = new Child();

console.log(child2.names); // ["kevin", "daisy", "yayu"]

2. 在创建 Child 的实例时，不能向Parent传参

借用构造函数(经典继承)

function Parent () {
    this.names = ['kevin', 'daisy'];
}

function Child () {
    Parent.call(this);
}

var child1 = new Child();

child1.names.push('yayu');

console.log(child1.names); // ["kevin", "daisy", "yayu"]

var child2 = new Child();

console.log(child2.names); // ["kevin", "daisy"]

优点：

1. 避免了引用类型的属性被所有实例共享
2. 可以在 Child 中向 Parent 传参

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

function Child (name) {
    Parent.call(this, name);
}

var child1 = new Child('kevin');

console.log(child1.name); // kevin

var child2 = new Child('daisy');

console.log(child2.name); // daisy

缺点：
方法都在构造函数中定义，每次创建实例都会创建一遍方法。

组合继承(原型链和经典继承)

function Parent (name) {
    this.name = name;
    this.colors = ['red', 'blue', 'green'];
}

Parent.prototype.getName = function () {
    console.log(this.name)
}

function Child (name, age) {

    Parent.call(this, name);
    
    this.age = age;

}

Child.prototype = new Parent();
Child.prototype.constructor = Child;

var child1 = new Child('kevin', '18');

child1.colors.push('black');

console.log(child1.name); // kevin
console.log(child1.age); // 18
console.log(child1.colors); // ["red", "blue", "green", "black"]

var child2 = new Child('daisy', '20');

console.log(child2.name); // daisy
console.log(child2.age); // 20
console.log(child2.colors); // ["red", "blue", "green"]

优点：融合原型链继承和构造函数的优点，是 JavaScript 中最常用的继承模式。

class继承

class Parent{
  constructor(name1){
    this.name1 = name1
  }
  pMethod(){
    console.log(this.name1)
  }
}
class Child extends Parent{ //用 A extends B 来创建父子关系
  constructor(name2, name1){
    super(name1) //super 关键字调用父对象上的函数
    this.name2 = name2 //使用 this 之前，必须先调用super()，否则会抛出错误
  }
  cMethod(){
    console.log(this.name2)
  }
}

let fn = new Child('hee', 'jack')
fn.pMethod() //jack
fn.cMethod() //hee