My answers of the game: http://toys.usvsth3m.com/javascript-under-pressure/

Q1.js

function doubleInteger(i) {
  // i will be an integer. Double it and return it.
  return i * 2
}

Q2.js

function isNumberEven(i) {
  // i will be an integer. Return true if it's even, and false if it isn't.
  return i % 2 === 0
}

Q3.js

function getFileExtension(i) {
  // i will be a string, but it may not have a file extension.
  // return the file extension (with no period) if it has one, otherwise false
  var m = i.match(/^.*\.([a-z]+)$/)
  return !!m && m[1]
}

Q4.js

function longestString(i) {
  // i will be an array.
  // return the longest string in the array
  return i.filter(function(item) {
    return typeof item === 'string'
  }).sort(function(x, y) {
    return x.length > y.length
  }).pop()
}

Q5.js

function arraySum(i) {
  // i will be an array, containing integers, strings and/or arrays like itself.
  // Sum all the integers you find, anywhere in the nest of arrays.
  var ret = [], flatten

  (flatten = function(arr) {
    arr.forEach(function(item) {
      if (Array.isArray(item)) {
        flatten(item)
      }
      else if (typeof item === 'number') {
        ret.push(item)
      }
    })
  })(i)

  return ret.reduce(function(memo, item) {
    return memo + item
  })
}