hasLocalStorageKey

1/**
2 * Checks if a specific key exists in localStorage.
3 *
4 * @param key - The key to check for existence.
5 * @returns True if the key exists, false otherwise.
6 */
7export function hasLocalStorageKey(key: string): boolean {
8  return localStorage.getItem(key) !== null;
9}

• Lightweight Key Check

  Provides a fast and efficient way to check for key existence without parsing or modifying stored data.

• Avoids Side Effects

  Pure read-only access — does not alter or mutate localStorage, preserving state integrity.

• Simplifies Conditional Logic

  Enables cleaner flow control when deciding whether to load or initialize stored values.

• Zero-Dependency Utility

  Doesn’t rely on additional abstractions or libraries; directly leverages native Web APIs.

Tests | Examples

1const key = 'testKey';
2
3beforeEach(() => {
4  localStorage.clear();
5});
6
7test('returns true if key exists in localStorage', () => {
8  localStorage.setItem(key, 'value');
9  expect(hasLocalStorageKey(key)).toBe(true);
10});
11
12test('returns false if key does not exist in localStorage', () => {
13  expect(hasLocalStorageKey('missingKey')).toBe(false);
14});
15
16test('returns true for existing key with null string value', () => {
17  localStorage.setItem(key, 'null');
18  expect(hasLocalStorageKey(key)).toBe(true);
19});
20
21test('returns true for existing key with empty string value', () => {
22  localStorage.setItem(key, '');
23  expect(hasLocalStorageKey(key)).toBe(true);
24});

Common Use Cases

• Feature Initialization Guards

  Determine whether user-specific settings or app state need to be initialized.

• Safe Retrieval of Stored Data

  Check if data exists before calling loadFromLocalStorage to avoid fallback logic or exceptions.

• Debugging and Inspection

  Programmatically inspect if certain app state keys were written during a session.

• Conditional UI Rendering

  Show or hide UI elements (e.g. onboarding modals or notifications) based on presence of flags in localStorage.