--description--

Write a function to return the factorial of a number.

Factorial of a number is given by:

For example:

Note: 0! = 1

--hints--

factorial should be a function.

assert(typeof factorial === 'function');

factorial(2) should return a number.

assert(typeof factorial(2) === 'number');

factorial(3) should return 6.

assert.equal(factorial(3), 6);

factorial(5) should return 120.

assert.equal(factorial(5), 120);

factorial(10) should return 3,628,800.

assert.equal(factorial(10), 3628800);

--seed--

--seed-contents--

function factorial(n) {

}

--solutions--

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