Number.prototype.toCurrency = function() {
    var value;
    if (isNaN(this) || !isFinite(this)) {
      return '-';
    }
    value = Math.abs(this).toFixed(2);
    value = value.replace(/(\d)(?=(\d\d\d)+(?!\d))/g, '$1,');
    return (this < 0 ? '-$' : '$') + value;
  };

  Number.prototype.toPercent = function() {
    if (isNaN(this) || !isFinite(this)) {
      return '-';
    }
    return Math.abs(this * 100).toFixed(2) + '%';
  };