fix(luhn): empty input should return false

Author: webdeveric

src/luhn.ts

@@ -1,8 +1,8 @@
 export function luhn(input: number | bigint | string): boolean {
   const value = typeof input === 'string' ? input : String(input);
 
-  // input contained non digit characters.
-  if (/[^\d]/.test(value)) {
+  // value is empty or contained non digit characters.
+  if (!value.length || /\D/.test(value)) {
     return false;
   }
 

test/luhn.test.ts

@@ -18,8 +18,8 @@ describe('luhn()', () => {
     expect(luhn(4000000000001001)).toBeFalsy();
   });
 
-  it.each(['not a credit card number', '-1', Number.POSITIVE_INFINITY, Number.NEGATIVE_INFINITY])(
-    'returns false when giving bad input: %s',
+  it.each(['', ' ', 'not a credit card number', '-1', Number.POSITIVE_INFINITY, Number.NEGATIVE_INFINITY])(
+    'returns false when giving bad input: "%s"',
     (input) => {
       expect(luhn(input)).toBeFalsy();
     },