a.js

function fib(n) {
  var a = 1, b = 0, p = 0, q = 1, c = n, tmp_1, tmp_2;

  while (c > 0) {
    if (c % 2 === 0) {
      tmp_1 = p * p + q * q;
      tmp_2 = (q + 2 * p) * q;
      p = tmp_1;
      q = tmp_2;
      c = c / 2;
    } else {
      tmp_1 = (a + b) * q + a * p;
      tmp_2 = a * q + b * p;
      a = tmp_1;
      b = tmp_2;
      c--;
    }
  }
  return b;
}

var sys = require('sys');
sys.print(fib(50)+"\n");

b.rb

class Fibonacci
  attr_accessor :memo
  def initialize
    @memo = [0 , 1]
  end

  def cal(n)
    @memo.size.upto(n){|i| @memo[i] = @memo[i - 1] + @memo[i - 2]}
    puts @memo[n]
  end
end

Fibonacci.new.cal(50)

c.md

.-[17:11] asonas:~/dev/tmp/fib (master)
`-% node -v
v0.10.28
.-[17:11] asonas:~/dev/tmp/fib (master)
`-% ruby -v
ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-darwin13.0]
.-[17:11] asonas:~/dev/tmp/fib (master)
`-% time ruby fib.rb
12586269025
ruby fib.rb  0.04s user 0.03s system 79% cpu 0.083 total
.-[17:11] asonas:~/dev/tmp/fib (master)
`-% time node fib.js
12586269025
node fib.js  0.02s user 0.01s system 96% cpu 0.034 total