JS 求階乘

//==================階乘=========================
var Vactorial = function() {
 var obj = new Object();
 obj.total = 1;
 obj.start = function( r ) {
  if(!/^/d+$/.test(r)){return "請輸入正整數！";}
  obj.total = obj.total * r;
  if(r>1){
   obj.start(r-1);
  }
  return obj.total;
 } 
 return obj;
}
var v = new Vactorial();
alert( v.start( 0 ) );