throw-error-for-negative-factorial

src/algorithms/math/factorial/__test__/factorial.test.js

@@ -3,9 +3,14 @@ import factorial from '../factorial';
 describe('factorial', () => {
   it('should calculate factorial', () => {
     expect(factorial(0)).toBe(1);
+    expect(factorial(-0)).toBe(1);
     expect(factorial(1)).toBe(1);
     expect(factorial(5)).toBe(120);
     expect(factorial(8)).toBe(40320);
     expect(factorial(10)).toBe(3628800);
   });
+  it('should throw exception', () => {
+    expect(() => factorial(-1)).toThrowError('Factorial of a negative number (-1) does not exist!');
+    expect(() => factorial(-10)).toThrowError('Factorial of a negative number (-10) does not exist!');
+  });
 });

src/algorithms/math/factorial/__test__/factorialRecursive.test.js

@@ -3,9 +3,14 @@ import factorialRecursive from '../factorialRecursive';
 describe('factorialRecursive', () => {
   it('should calculate factorial', () => {
     expect(factorialRecursive(0)).toBe(1);
+    expect(factorialRecursive(-0)).toBe(1);
     expect(factorialRecursive(1)).toBe(1);
     expect(factorialRecursive(5)).toBe(120);
     expect(factorialRecursive(8)).toBe(40320);
     expect(factorialRecursive(10)).toBe(3628800);
   });
+  it('should throw exception', () => {
+    expect(() => factorialRecursive(-1)).toThrowError('Factorial of a negative number (-1) does not exist!');
+    expect(() => factorialRecursive(-10)).toThrowError('Factorial of a negative number (-10) does not exist!');
+  });
 });

src/algorithms/math/factorial/factorial.js

@@ -3,6 +3,7 @@
  * @return {number}
  */
 export default function factorial(number) {
+  if (number < 0) throw new Error(`Factorial of a negative number (${number}) does not exist!`);
   let result = 1;
 
   for (let i = 2; i <= number; i += 1) {

src/algorithms/math/factorial/factorialRecursive.js

@@ -3,5 +3,6 @@
  * @return {number}
  */
 export default function factorialRecursive(number) {
+  if (number < 0) throw new Error(`Factorial of a negative number (${number}) does not exist!`);
   return number > 1 ? number * factorialRecursive(number - 1) : 1;
 }