--description--

In this lab, you will build a countdown function that takes a starting number and generates a countdown list.

When you call countdown(n), it should return an array that starts at n and counts down by 1 until it reaches 1.

For example:

• countdown(5) should return [5, 4, 3, 2, 1]
• countdown(1) should return [1]

If the starting number is less than 1, there is nothing to countdown, so return an empty array:

• countdown(0) should return []
• countdown(-3) should return []

To complete the lab, you must build the result using recursion and you must not use loops (for, while), Array.from(), or array-iteration methods (forEach, map, filter, reduce). Each call should produce its own result array (don't use globals to store the countdown).

Objective: Fulfill the user stories below and get all the tests to pass to complete the lab.

User Stories:

1. You should create a function named countdown.
2. The countdown function should take a single argument n (a number).
3. If n is less than 1, countdown should return an empty array.
4. Otherwise, countdown should return an array containing the integers from n down to 1 in descending order.
5. You must use recursion (the function should call itself) and must not use loops of any kind (for, while, Array.from(), or higher-order methods like forEach, map, filter, reduce).
6. Each recursive call should use a smaller value than the previous call (for example, n - 1) so the function reaches its base case.
7. The solution should not use global variables to store or cache the result array.
8. Calling countdown multiple times with different inputs should always return the correct, independent result.

--hints--

You should have a function named countdown.

assert.isFunction(countdown);

countdown(-1) should return an empty array.

assert.isEmpty(countdown(-1));

countdown(10) should return [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

assert.deepStrictEqual(countdown(10), [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]);

countdown(5) should return [5, 4, 3, 2, 1]

assert.deepStrictEqual(countdown(5), [5, 4, 3, 2, 1]);

Your code should not rely on any kind of loops (for, while, Array.from() or higher order functions such as forEach, map, filter, and reduce).

assert(
  !__helpers.removeJSComments(code).match(/for|while|forEach|map|filter|reduce|Array\.from/g)
);

You should use recursion to solve this problem.

assert.isAtLeast(
  __helpers.removeJSComments(countdown.toString()).match(/countdown\s*\(.+\)/g)?.length,
  2
);

Global variables should not be used to cache the array.

countdown(1)
assert.deepStrictEqual(countdown(5), [5, 4, 3, 2, 1]);

--seed--

--seed-contents--

--solutions--

function countdown(n) {
  if (n < 1) {
    return [];
  }

  return [n, ...countdown(n - 1)];
}