A quicksort implementation in CoffeeScript

quicksort.coffee

arr = [900, 1, 39, 12, 8, 15, 39, 11, 100]

quicksort = (arr) ->
  if(arr.length < 2) 
    return arr

  unless arr or arr.length > 1 
    throw new Error 'Input invalid'

  pivot = arr[0]
  left = []
  right = []
  i = 0

  for num in arr
    left.push num if num < pivot
    right.push num if num > pivot

  _.union(quicksort(left), [pivot], quicksort right)