feat/ update function to not accept strings

Author: nik-rev

13_factorial/README.md

@@ -5,8 +5,7 @@ Write a recursive function that takes a non-negative integer, and returns the pr
 For example:
 
 ```javascript
-factorial(2); // 2 * 1, Output: 2
-factorial('4'); // 4 * 3 * 2 * 1, Output: 24
+factorial('4'); // Output: undefined
 factorial(5); // 5 * 4 * 3 * 2 * 1, Output: 120
 factorial(7.2); // Output: undefined
 factorial(0); // Output: 1

13_factorial/factorial.spec.js

@@ -25,16 +25,7 @@ describe('factorial', () => {
   test.skip('doesn\'t accept floats', () => {
     expect(factorial(5.4)).toBe(undefined);
   });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("0")).toBe(1);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("1")).toBe(1);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("2")).toBe(2);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("8")).toBe(40320);
+  test.skip('doesn\'t accept strings', () => {
+    expect(factorial('5')).toBe(undefined);
   });
 });

13_factorial/solution/factorial-solution.js

@@ -1,12 +1,6 @@
 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) return 1;
+  if (!Number.isInteger(n) || n < 0) return;
+  if (n === 0) return 1;
   return n * factorial(n - 1);
 };
 

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

@@ -25,16 +25,7 @@ describe('factorial', () => {
   test.skip('doesn\'t accept floats', () => {
     expect(factorial(5.4)).toBe(undefined);
   });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("0")).toBe(1);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("1")).toBe(1);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("2")).toBe(2);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(factorial("8")).toBe(40320);
+  test.skip('doesn\'t accept strings', () => {
+    expect(factorial('5')).toBe(undefined);
   });
 });