CODE EXAMPLE FOR JAVASCRIPT

js how to calculate factorial

// @ts-check
/* ---------------------------------- using a loop --------------------------------- */
(() => {
  function factorial(n) {
    if (n < 0) return;

    let result = 1;

    for (let i = 2; i <= n; i++) {
      result *= i;
    }

    return result;
  }

  console.log(factorial(4)); // => 24
  console.log(factorial(0)); // => 1
  console.log(factorial(-2)); // => undefined
})();

/* ------------------------------ recursive way----------------------------- */
(() => {
  function factorial(n) {
    if (n < 0) return;
    if (n == 0) return 1;

    return n == 1 ? 1 : n * factorial(n - 1);
  }

  console.log(factorial(5)); // => 120
  console.log(factorial(0)); // => 1
})();