Extend's Constructor can't find config parm?

Dear:

In the follow code，It's show "Uncaught ReferenceError: config is not defined " on chrome's console.

why?

thx

Code:

function Vehicle(config){
   this.x=config.x;
   this.y=config.y;

}

Vehicle.prototype.move=function(dx,dy){
   this.x +=dx;
   this.y +=dy;
};

Vehicle.prototype.toString=function(){
   return "point:"+x+","+y;
};

var Car=Ext.extend(Vehicle,{   
     constructor:function(){  
       Vehicle.prototype.constructor.call(this,config);
       this.color=config.color;
     },move:function(dx){   
         this.x=dx;
     },toString:function(){
        var str="Car is "+ this.x + " miles away from the origial position.";
        str +=" this car is :"+this.colr;
        return str;
     }
   
});


var carConfig={
    x:10,
    y:0,
    color:"white"
};

var car= new Car(carConfig);
car.move(150);
console.info(car.toString());