类：面向对象编程

面向类的设计模式：实例化（instantiation）、继承（inheritance）和（相对）多态 （polymorphism）。

寄生继承

function Vehicle(){    
    this.engines = 1;
}
Vehicle.prototype.ignition = function(){
      console.log("Turning on my engine.");
};
Vehicle.prototype.drive = function(){    
    this.ignition();
    console.log("Steering and moving forward!");
};
//“寄生类” Car
function Car(){
    var car = new Vehicle();
    car.wheels = 4;
    var vehDrive = car.drive;
    car.drive = function(){    
      vehDrive.call(this);    
      console.log("Rolling on all "+this.wheels+"wheels!");
      return car;    
}
var myCar = new Car();
myCar.drive();
// Turning on my engine!
// Steering and moving forward!
// Rolling on all 4 wheels!

隐式混入

var Something={    
    cool:function(){
        this.greeting="Hello World";
        this.count=this.count ? this.count+1 : 1;    
        }
};
Something.cool();    
Something.greeting; //"Hello World"
Something.count;    //1
var Another={
    cool:function(){
            Something.cool.call(this);
        }
};
Another.cool();
Another.greeting; // "Hello World"
Another.count;    // 1 (count不是共享状态）