Javascript Array sum(begin, end)

Array.prototype.sum = function(begin, end) {
 var total = 0;//  ww w .ja va 2  s.  c  o  m

 for (var i = begin >> 0 || 0, len = end + 1 >> 0 || this.length >> 0; i < len; i++) {
  total += +this[i] || 0;
 }

 return total;
};