trampoline.js

function trampoline(f) {
  return function trampolined(...args) {
    let result = f.bind(null, ...args);

    while (typeof result === 'function') result = result();

    return result;
  };
}

function _factorial(n) {
  if (n <= 1) return 1;
  return n * _factorial(n - 1);
}


const factorial = trampoline(function _factorial(n, acc = 1) {
  if (n <= 1) return acc;
  return () => _factorial(n - 1, n * acc);
});

console.log(factorial(6));