SOURCE

function mixin(sourceObj,targetObj){
  for(var key in sourceObj){
    if(!(key in targetObj)){
      targetObj[key] = sourceObj[key];
    }
  }
  
  return targetObj;
}

var Vehicle = {
  engines:1,
  
  ignition:function(){
    console.log("truning on my engine");
  },
    
  drive:function(){
    this.ignition();
    console.log("Steering and moving forward!")
  }  
}

var Car = mixin(Vehicle, {
  wheels:4,
  
	ignition:function(){
    console.log("truning on car engine");
  },
	
  drive:function(){
		// 显式多态
    Vehicle.drive.call(this);
    console.log(
      "Rolling on all "+this.wheels+" wheels"
    );
  }
})

Car.drive();