isValidUsername
Validates whether a username meets common criteria.
1/**
2 * Validates whether a username meets common criteria.
3 *
4 * Rules:
5 * - 3 to 20 characters long
6 * - Only letters, numbers, underscores, and dots
7 * - Cannot start or end with a dot or underscore
8 * - Cannot have consecutive dots or underscores
9 *
10 * @param username - The string to validate.
11 * @returns True if valid, false otherwise.
12 */
13export function isValidUsername(username: string): boolean {
14 if (!/^[a-zA-Z0-9._]{3,20}$/.test(username)) return false;
15 if (/^[._]/.test(username) || /[._]$/.test(username)) return false;
16 if (/(\.\.|__)/.test(username)) return false;
17 return true;
18}Comprehensive Rule Enforcement
Enforces multiple common constraints in a clear, layered manner-covering length, allowed characters, and structural rules.
Readable & Maintainable Logic
Splits validation into small, expressive checks rather than a single complex regex, improving maintainability and clarity.
Performance-Efficient
Uses simple and efficient regex checks with minimal overhead, ideal for real-time validation (e.g., on input change).
Minimizes User Input Errors
Prevents common formatting mistakes like leading/trailing or repeated special characters early in the user experience.
Tests | Examples
1test('valid usernames', () => {
2 expect(isValidUsername('user_name')).toBe(true);
3 expect(isValidUsername('user.name')).toBe(true);
4 expect(isValidUsername('user123')).toBe(true);
5 expect(isValidUsername('abc')).toBe(true);
6 expect(isValidUsername('user.name_99')).toBe(true);
7});
8
9test('invalid usernames - too short or long', () => {
10 expect(isValidUsername('ab')).toBe(false);
11 expect(isValidUsername('a'.repeat(21))).toBe(false);
12});
13
14test('invalid usernames - invalid characters', () => {
15 expect(isValidUsername('user-name')).toBe(false);
16 expect(isValidUsername('user@name')).toBe(false);
17 expect(isValidUsername('user name')).toBe(false);
18});
19
20test('invalid usernames - starts or ends with dot/underscore', () => {
21 expect(isValidUsername('_username')).toBe(false);
22 expect(isValidUsername('.username')).toBe(false);
23 expect(isValidUsername('username_')).toBe(false);
24 expect(isValidUsername('username.')).toBe(false);
25});
26
27test('invalid usernames - consecutive dots or underscores', () => {
28 expect(isValidUsername('user..name')).toBe(false);
29 expect(isValidUsername('user__name')).toBe(false);
30});Common Use Cases
User Registration Forms
Validate usernames during sign-up to prevent invalid or unsafe identifiers.
Profile Update Interfaces
Re-validate modified usernames before saving changes.
Admin Dashboards
Check for proper formatting when creating or editing users from an admin panel.
Pre-Validation for API Requests
Sanitize and validate usernames before submitting to backend services or storing in a database.