第六章（3）：继承

继承的几种方式

• 原型链

 /**
   * 原型链继承
   * 本质是重写原型对象
   * 缺点：引用类型值被实例共享
     * @constructor
     */
  function Super() {
    this.property = 'super'
    this.arr = [1,2]
  }

  Super.prototype.getValue = function () {
    return this.property
  }

  function Sub() {

  }

  Sub.prototype = new Super();

  let sub = new Sub()
  console.log(sub.getValue())  // super

  console.log(Super.prototype.isPrototypeOf(sub)) // true
  console.log(Sub.prototype.isPrototypeOf(sub)) // true
  console.log(Object.prototype.isPrototypeOf(sub)) // true

  let sub1 = new Sub()
  sub1.arr.push(3);

  let sub2 = new Sub()
  console.log(sub1.arr) // [1,2,3]
  console.log(sub2.arr) // [1,2,3]

原型链示意图：

• 构造函数

/**
   * 借用构造函数模式
   * 问题：函数无法复用
     * @constructor
     */
    function SuperInstance() {
    this.color = ['red', 'yellow']
  }

  function SubInstance() {
    SuperInstance.call(this)
  }

  var si = new SubInstance();
    var si1 = new SubInstance();

    si.color.push("black");
    console.log(si.color) //  ["red", "yellow", "black"]
    console.log(si1.color)  //  ["red", "yellow"]

• 组合继承(将原型链和构造函数组合在一起)

/**
   * 组合模式继承
   * 最常用的模式
     * @param name
     * @constructor
     */
  function SuperCombination(name) {
        this.name = name;
    this.color = ['red', 'yellow'];
  }

  SuperCombination.prototype.getName = function () {
    return this.name;
  }

  function SubCombination(name, age) {
    SuperCombination.call(this, name)
    this.age = age
  }

  SubCombination.prototype = new SuperCombination();
//  SubCombination.prototype.constructor = SubCombination;

  SubCombination.prototype.sayAge = function () {
    return this.age;
  }

  let sc = new SubCombination('日暮途远', 18);
  let sc1 = new SubCombination('Tiptoe', 20);

  sc.color.push('black');

  console.log(sc.color, sc.getName(), sc.sayAge()) // ["red", "yellow", "black"] "日暮途远" 18
  console.log(sc1.color, sc1.getName(), sc1.sayAge()) //  ["red", "yellow"] "Tiptoe" 20

• 原型式继承

    /**
     * 原型式继承
     * 缺点： 引用类型共享
     * @type {{name: string, sayName: person.sayName, game: [string,string]}}
     */
    var person = {
        name: '日暮途远',
        sayName: function () {
            return this.name;
        },
        game: ['英雄联盟', '王者荣耀']
    }

    var o = Object.create(person);
    console.log(o.sayName()); // 日暮途远

    o.game.push('战地')
    console.log(person.game)  // ["英雄联盟", "王者荣耀", "战地"]

• 寄生式组合继承

/**
   * 寄生组合式继承
   * 优点：避免2次调用父类构造函数
     * @param subType
     * @param superType
     */
  function inherit(subType, superType) {
    var property = Object.create(superType.prototype);
    property.constructor = subType;
    subType.prototype = property;
  }

  function SuperIn(name) {
    this.name = name
  }

  SuperIn.prototype.sayName = function () {
    return this.name;
  }

  function SubIn(name, age) {
    SuperIn.call(this, name)
    this.age = age
  }

  inherit(SubIn, SuperIn)

  SubIn.prototype.sayAge = function () {
    return this.age;
  }

  let sI = new SubIn('日暮途远', 18)
  console.log(sI.sayName()) // 日暮途远

引用

javascript高级程序设计第三版