JavaScript Prototype

function Obj () {
}
Obj.a=0;
Obj.fn=function(){
}
console.log(Obj.a);    //0
console.log(typeof Obj.fn);//function
var o=new Obj();
console.log(o.a);//undefined
console.log(typeof o.fn);//undefined

function Obj(){
this.a=[];
this.fn=function(){

}
}

var o1=new Obj();
o1.a.push(1);
o1.fn={};
console.log(o1.a);
console.log(typeof o1.fn);
var o2=new Obj();
console.log(o2.a);
console.log(typeof o2.fn);