Javascript Number isMultipleof(num)

var result = 0;//from w  ww . jav  a2  s  .  c  om

Number.prototype.isMultipleof = function (num) {
  if (this % num === 0) {
    return true;
  }
  return false;
}

for (var i = 1; i < 1000; i++) {
  if (i.isMultipleof(3) || i.isMultipleof(5) ) {
    result += i;
  }
}

console.log(result);