每日靈魂一問-繼承的6種方法（下）

四.原型式繼承（Object.create）

let parent4 = {
    name: "parent4",
    friends: ["p1", "p2", "p3"],
    getName: function() {
      return this.name;
    }
  };

  let person4 = Object.create(parent4);
  person4.name = "tom";
  person4.friends.push("jerry");

  let person5 = Object.create(parent4);
  person5.friends.push("lucy");

  console.log(person4.name); // tom
  console.log(person4.name === person4.getName()); // true
  console.log(person5.name); // parent4
  console.log(person4.friends); // ["p1", "p2", "p3","jerry","lucy"]
  console.log(person5.friends); // ["p1", "p2", "p3","jerry","lucy"]

缺點：淺拷貝，多個實例的引用類型屬性指向相同的內存

五. 寄生式繼承

let parent5 = {
    name: "parent5",
    friends: ["p1", "p2", "p3"],
    getName: function() {
        return this.name;
    }
};

function clone(original) {
    let clone = Object.create(original);
    clone.getFriends = function() {
        return this.friends;
    };
    return clone;
}

let person5 = clone(parent5);
let person6 = clone(parent5);

person5.name = '22';
person5.friends.push(22);
console.log(person5.getName()); // parent5
console.log(person5.getFriends()); // ["p1", "p2", "p3", 22]
console.log(person6.getName()); // parent5
console.log(person6.getFriends()); // ["p1", "p2", "p3", 22]

缺點：淺拷貝，多個實例的引用類型屬性指向相同的內存

六.寄生組合式繼承 (全場最佳）

function clone (parent, child) {
    // 這裏改用 Object.create 就能夠減小組合繼承中多進行一次構造的過程
    child.prototype = Object.create(parent.prototype);
    child.prototype.constructor = child;
}

function Parent6() {
    this.name = 'parent6';
    this.play = [1, 2, 3];
}
Parent6.prototype.getName = function () {
    return this.name;
}
function Child6() {
    Parent6.call(this);
    this.friends = 'child5';
}

clone(Parent6, Child6);

Child6.prototype.getFriends = function () {
    return this.friends;
}

let person6 = new Child6(); 
console.log(person6); //{friends:"child5",name:"child5",play:[1,2,3],__proto__:Parent6}
console.log(person6.getName()); // parent6
console.log(person6.getFriends()); // child5