fib.js

fib.js

function fibonacci(n) {
 return Math.round((Math.pow((1 + Math.sqrt(5)) / 2, n) - Math.pow(-2 / (1 + Math.sqrt(5)), n)) / Math.sqrt(5));
}

function trampoline(f) {
  return function (...args){
      var result = f( ...args )
      while (typeof result === "function") {
          result = result()
      }
      return result
  }
}
function fib (n) {
    return trampoline(function inner_fib(n, a, b) {
        if (n === 0) {return a;}
        if (n === 1) {return b;}
        return () => inner_fib(n - 1, b, a + b);
    })(n, 0, 1);
}