recursive.js

var depth = 0;

function f(x, y, z) {
  if(y < x) {
    ++depth
    console.log("Recursion depth: %d", depth)
    z = f(f(x - 1, y, z), f(y - 1, z, x), f(z - 1, x, y))
    --depth
  }
  return z
}

var x = 18, y = 12, z = 6

f(x, y, z)