feat(curriculum); added another challenge to help teach recursion (#35966)

* Squashed the removal of the before test section

* fix: changed blockquote triple backtick syntax

* fix: removed recursion explanation

* fix: changed meta title and thru to through

* fix: capitalize "after" in several strings

curriculum/challenges/_meta/basic-javascript/meta.json

@@ -443,6 +443,10 @@
     [
       "5cc0bd7a49b71cb96132e54c",
       "Use Recursion to Create a Range of Numbers"
+    ],
+    [
+      "5cd9a70215d3c4e65518328f",
+      "Use Recursion to Create a Countdown"
     ]
   ],
   "helpRoom": "HelpJavaScript",

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/use-recursion-to-create-a-countdown.md

@@ -0,0 +1,91 @@
+---
+id: 5cd9a70215d3c4e65518328f
+title: Use Recursion to Create a Countdown
+challengeType: 1
+---
+
+## Description
+<section id='description'>
+
+Continuing from the previous challenge, we provide you another opportunity to create a recursive function to solve a problem.
+
+</section>
+
+## Instructions
+<section id='instructions'>
+
+We have defined a function called <code>countdown</code> with two parameters.  The function should take an array in the <code>myArray</code> parameter and append the numbers n through 1 based on the <code>n</code> parameter.  
+For example, calling this function with <code>n = 5</code> will pad the array with the numbers <code>[5, 4, 3, 2, 1]</code> inside of it.
+Your function must use recursion by calling itself and must not use loops of any kind.
+
+</section>
+
+## Tests
+<section id='tests'>
+
+``` yml
+tests:
+  - text: After calling <code>countdown(myArray, -1)</code>, myArray should be empty.
+    testString: assert.isEmpty(padArray([], -1));
+  - text: After calling <code>countdown(myArray, 10)</code>, myArray should contain <code>[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]</code>
+    testString: assert.deepStrictEqual(padArray([], 10), [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]);
+  - text: After calling <code>countdown(myArray, 5)</code>, myArray should contain <code>[5, 4, 3, 2, 1]</code>
+    testString: assert.deepStrictEqual(padArray([], 5), [5, 4, 3, 2, 1]);
+  - text: Your code should not rely on any kind of loops (<code>for</code> or <code>while</code> or higher order functions such as <code>forEach</code>, <code>map</code>, <code>filter</code>, or <code>reduce</code>.).
+    testString: assert(!removeJSComments(code).match(/for|while|forEach|map|filter|reduce/g));
+  - text: You should use recursion to solve this problem.
+    testString: assert(removeJSComments(countdown.toString()).match(/countdown\s*\(.+\)\;/));
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+
+
+//Only change code below this line
+function countdown(myArray, n){
+  return;
+}
+
+```
+
+</div>
+
+### After Test
+<div id='js-teardown'>
+
+```js
+const removeJSComments = str => str.replace(/\/\*[\s\S]*?\*\/|\/\/.*$/gm, '');
+function padArray(arr, n){
+  countdown(arr, n);
+  return arr;
+}
+
+```
+
+</div>
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+//Only change code below this line
+function countdown(myArray, n){
+  if(n <= 0){
+    return;
+  }
+  else{
+    myArray.push(n);
+    countdown(myArray, n - 1);
+  }
+}
+```
+
+</section>