---
title: Factorial
id: 597b2b2a2702b44414742771
challengeType: 5
---

## Description
<section id='description'>
<p>Write a function to return the factorial of a number.</p>
<p>Factorial of a number is given by : </p>
n! = n * (n-1) * (n-2) * ..... * 1
<p>
For example :
3! = 3*2*1 = 6
4! = 4*3*2*1 = 24
</p>
<p>Note :
0! = 1
</p>
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>factorial</code> is a function.
    testString: 'assert(typeof factorial === "function", "<code>factorial</code> is a function.");'
  - text: <code>factorial(2)</code> should return a number.
    testString: 'assert(typeof factorial(2) === "number", "<code>factorial(2)</code> should return a number.");'
  - text: <code>factorial(3)</code> should return 6.")
    testString: 'assert.equal(factorial(3),results[0],"<code>factorial(3)</code> should return 6.");'
  - text: <code>factorial(3)</code> should return 120.")
    testString: 'assert.equal(factorial(5),results[1],"<code>factorial(3)</code> should return 120.");'
  - text: '<code>factorial(3)</code> should return 3,628,800.")'
    testString: 'assert.equal(factorial(10),results[2],"<code>factorial(3)</code> should return 3,628,800.");'

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function factorial (n) {
  // Good luck!
}
```

</div>


### After Test
<div id='js-teardown'>

```js
console.info('after the test');
```

</div>

</section>

## Solution
<section id='solution'>


```js
function factorial(n) {
  let sum = 1;
  while (n > 1) {
    sum *= n;
    n--;
  }
  return sum;
}


```

</section>