fix(sample): include "undefined" in return union type

Author: screendriver

src/array/sample.spec.ts

@@ -1,10 +1,19 @@
-import { describe, expect, it } from 'vitest';
+import { assert, describe, expect, it } from 'vitest';
 import { sample } from './sample';
 
 describe('sample', () => {
   it('selects a random element from an array', () => {
     const arr = [1, 2, 3, 4, 5];
 
-    expect(arr.includes(sample(arr))).toBe(true);
+    const randomElement = sample(arr);
+
+    assert(randomElement !== undefined);
+    expect(arr.includes(randomElement)).toBe(true);
+  });
+
+  it('returns undefined when given array is empty', () => {
+    const arr: number[] = [];
+
+    expect(sample(arr)).toBe(undefined);
   });
 });

src/array/sample.ts

@@ -12,7 +12,7 @@
  * const randomElement = sample(array);
  * // randomElement will be one of the elements from the array, selected randomly.
  */
-export function sample<T>(arr: readonly T[]): T {
+export function sample<T>(arr: readonly T[]): T | undefined {
   const randomIndex = Math.floor(Math.random() * arr.length);
   return arr[randomIndex];
 }