feat/ add comments

Author: nik-rev

13_factorial/factorial.spec.js

@@ -13,7 +13,7 @@ describe('factorial', () => {
   test.skip('15th factorial number is 1307674368000', () => {
     expect(factorial(15)).toBe(1307674368000);
   });
-  test.skip('25th factorial number is 1.5511210043330986e+255', () => {
+  test.skip('25th factorial number is 1.5511210043330986e+25', () => {
     expect(factorial(25)).toBe(1.5511210043330986e+25);
   });
   test.skip('0th factorial number is 1', () => {

13_factorial/solution/factorial-solution.js

@@ -1,5 +1,11 @@
 const factorial = function(n) {
+  // a negative number will always contain a '-'
+  // a non-integer will always contain a '.'
+  // the [-.] regex literal will match strings that contain a '-' or a '.'
+  // n + '' converts n to a string, which is required for the Regex.prototype.test method 
   if (/[-.]/.test(n + '')) return;
+
+  // +n converts n to a number
   if (+n === 0 || +n === 1) return 1;
   return n * factorial(n - 1);
 };

13_factorial/solution/factorial-solution.spec.js

@@ -13,7 +13,7 @@ describe('factorial', () => {
   test.skip('15th factorial number is 1307674368000', () => {
     expect(factorial(15)).toBe(1307674368000);
   });
-  test.skip('25th factorial number is 1.5511210043330986e+255', () => {
+  test.skip('25th factorial number is 1.5511210043330986e+25', () => {
     expect(factorial(25)).toBe(1.5511210043330986e+25);
   });
   test.skip('0th factorial number is 1', () => {