function getArrayKeyIndex(arr, keyToFind) {
  var i = 0,
    key
  for (key in arr) {
    if (arr[key] === keyToFind) {
      return i
    }
    i++
  }
  return null
}
Given an array and the key to find, returns its index
@function
@ignore
@argument {Array} arr
@argument keyToFind
@returns index or null