Find Factorial in JavaScript

What You’ll Learn

Factorial n! is the product of integers from 1 through n, with 0! = 1. This tutorial covers recursive and iterative solutions, BigInt factorial, a live preview, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a nonnegative integer n, compute n!.

# 0! = 1
# 5! = 5 * 4 * 3 * 2 * 1 = 120
# 6! = 6 * 5! = 720

Inputs & Outputs

Minimal workflow

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

Method comparison

🔮 Live Preview

Exact factorial for 0 ≤ n ≤ 20 (safe to display exactly in JavaScript).

Press “Compute n!”.

Examples Gallery

Three complete JavaScript programs with Try it Yourself editors — recursive, iterative, and BigInt exact factorial. Click View Output to reveal sample console results.

function factorialRecursive(n) {
  if (n < 0) {
    throw new Error("Factorial is not defined for negative integers.");
  }
  if (n <= 1) {
    return 1;
  }
  return n * factorialRecursive(n - 1);
}

const number = 5;
const result = factorialRecursive(number);
console.log(`Factorial of ${number} is: ${result}`);

Factorial of 5 is: 120

function factorialIterative(n) {
  if (n < 0) {
    throw new Error("Factorial is not defined for negative integers.");
  }
  let result = 1;
  for (let i = 2; i <= n; i++) {
    result *= i;
  }
  return result;
}

const number = 5;
console.log(`Factorial of ${number} is: ${factorialIterative(number)}`);

Factorial of 5 is: 120

function factorialBigInt(n) {
  if (n < 0) {
    throw new Error("Factorial is not defined for negative integers.");
  }
  let result = 1n;
  for (let i = 2n; i <= BigInt(n); i++) {
    result *= i;
  }
  return result;
}

for (const n of [0, 1, 5, 10, 20]) {
  console.log(`${n}! = ${factorialBigInt(n)}`);
}

0! = 1
1! = 1
5! = 120
10! = 3628800
20! = 2432902008176640000

🔎 Worked Walkthrough — n = 5

Trace the recursive expansion for the classic interview value.

Final answer: 5! = 120.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

Both approaches use Θ(n) arithmetic operations for exact n!; stack usage is the key difference. Result size grows with n and is excluded from the “extra space” column above.

💡 Best Practices