gistfile1.js

function SubArray(length){
   Array.call(this); //"Magic"
   if(typeof length === "number" && length%1===0&&arguments.length===1){
     this.length = length; //Length has to be set manually for some reason.
   }
   else{
     var _len = arguments.length;
     this.length = _len;
     for(var i = 0; i<_len; i++)
        this[i] = arguments[i];
   }
}

SubArray.prototype = [];

SubArray.prototype.Length = function(len){
  if(typeof len === "number" && len%1===0)
  {
    this.length = len;
    return len;
  }
  var i = 0, truthy = true;
  while(truthy){
    truthy = (!!this[i++])||this.length >= i;
  }
  this.length = i;
  return i;
}


var x = new SubArray();