fibonacci.exs

defmodule Fib do

  def fib(n) when n < 2 do
    n
  end

  def fib(n) when n >= 2 do
    fib(n-1) + fib(n-2)
  end

end

fibonacci.js

function fibonacci (num) {
  if (num === 1 || num === 2) {
      return 1;
  }
  var temp =0, last1 = last2 = 1;
  for (var i=3; i<=num; i++) {
      temp = last1+last2;
      last2 = last1;
      last1 = temp;
  }
  return last1;
}