underPressure

function doubleInteger (arg) {
  return arg * 2;
}

function isNumberEven (arg) {
  return arg % 2 === 0;
}

function getFileExtension (arg) {
  return arg.split('.').length > 1 && arg.split('.').pop();
}

function longestString (arg) {
  return arg.reduce(function (max, s) {
    return s.substr && s.length > max.length ? s : max;
  }, '');
}

function arraySum (arg) {
  return (function it (a) {
    return a.reduce(function (sum, e) {
      return sum + (!e.substr && (e.length ? it(e) : e));
    }, 0);
  }(arg));
}