fibonacci-with-cache.js

var fibonacci = function(number) {
  var mem = {};

  function f(n) {
    var value;

    if (n in mem) {
      value = mem[n];
    }
    else {
      if (n === 0 || n === 1)
        value = n;
      else
        value = f(n - 1) + f(n - 2);

      mem[n] = value;
    }

    return value;
  }

  return f(number);
};