js继承

主要有原型链、借助构造函数、组合继承、原型式继承、寄生式继承、寄生组合继承6种，但是由于原型链、构造函数、原型式继承、寄生继承都有一定的缺点，并不常用，故此不在赘述。

• 组合继承

function super(name) { ???this.name = name; ???this.colors = ["red","blue"]; ???}super.prototype.sayName = function(){ ???alert(this.name);};function sub(name,age){ ???super.call(this,name); //属性继承 ?第二次调用super() ???this.age = age;}sub.prototype = new super(); //方法继承 第一次调用super()sub.prototype.sayAge = function(){ ???alert(this.age);};var instance1 = new sub("Barney",32);instance1.colors.push("balck");alert(instance1.colors);//red blue blackinstance1.sayName();//Barneyinstance1.sayAge();//32var instance1 = new sub("Ted",33);alert(instance1.colors);//red blueinstance1.sayName();//Tedinstance1.sayAge();//33

如上所示，两个实例之间的白能量并没有互相影响，而且都可以使用super和sub中的方法，但是super()被调用了两次,显得有些多余，所以有了原型式继承

• 寄生组合继承

  function inheritPrototype(subType,superType){ ???var prototype = Object(superType.prototype); ???prototype.constructor = subType; ???subType.prototype = prototype;}function super (name){ ???this.name = name; ???this.colors = ["red","blue"];}super.prototype.sayName = function(){ ???alert(this.name);};function sub(name,age){ ???super.call(this,name); ???this.age = age;}inheritPrototype(sub,super);sub.prototype.sayAge = function(){ ???alert(this.age);};var instance = new sub("Barney",32);instance.sayName();//Barneyinstance.sayAge();//32
  instance instanceof super; //false 不知道为什么会是false
  instance instanceof sub; //true