JS类的继承

1.类式继承

  function Person(name,age){
    this.name = name;
    this.age = age ;
    this.instances = ['1','2','3']
  }
  Person.prototype.getName = function(){}

  function Man(){}
  Man.prototype = new Person('jack',25);  //继承父类
  Man.prototype.getAge = function(){};
  
  var man = new Man();
  console.log(man instanceof Man); //true
  console.log(man instanceof Person); //true
  console.log(Man  instanceof Person); //false 这里并不是实例关系；是Man.prototype继承了Person
  console.log(Man.prototype instanceof Person); //true
  问题: 如果父类中的公共属性是引用类型,则会被所以实例共享，且被修改后同时做出变动;
  var man1 = new Man();
  console.log(man.instances );  // ['1','2','3']
  console.log(man1 .instances );   // ['1','2','3']
  man1.instances.push('4');
  console.log(man.instances );   // ['1','2','3','4']

2. 构造函数继承

  function Person(age){
    this.age = age ;
    this.instances = ['1','2','3']
  }
  Person.prototype.getName = function(){}

  function Man(sexy){
    Person.call(this,'13'); //使用call来完成
    this.sexy = sexy;
  }
  var man1 = new Man('s1');
  var man2 = new Man('s2');
  man1 .instances.push('4');
  console.log(man2.instances) ; //  ['1','2','3']；
  //不同的对象都进行了实例化
  man1 .getName() //TypeError 因为没有继承原型链
  

3.组合继承

   function Person(age){
    this.age = age ;
    this.instances = ['1','2','3']
  }
  Person.prototype.getName = function(){}

  function Man(sexy){
    Person.call(this,'13');
    this.sexy = sexy;
  }
  Man.prototype = new Person();
  注：组合继承是 类式继承与构造函数继承的结合;
  问题：调用了两边父类函数：call/new Person()

4.原型继承

  function inheritObject(o){
    function F(){};
    F.prototype = o;
    return new F(); //返回过度对象的一个实例，
  }
  var person = {
    name : 'jack',
    instances : ['1','2','3']
  }
  var p1 = inheritObject(person );
  p1.name = '111'; //111
  p1.instances.push('4'); // ["1", "2", "3", "4", "5"]
  var p2 = inheritObject(person );
  p2.name = '222';  //222
  p2.instances.push('5'); // ["1", "2", "3", "4", "5"]
  注： 与类式继承一样，引用类型的值被共享了

5.寄生式继承

  function inheritObject(o){
    function F(){};
    F.prototype = o;
    return new F(); //返回过度对象的一个实例，
  }
  var person = {
    name : 'jack',
    instances : ['1','2','3']
  }
  function createPerson(obj){
    var o = new inheritObject(obj);
    o.getName = function(){};
    return o;
  }

6.寄生组合式继承

  function inheritPrototype(subClass,SuperClass){
    var p = inheritObject(SuperClass.prototype);
    p.constructor = subClass;
    subClass.prototype = p;
  }