Validate Email in JavaScript

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function isValidEmail(email: string): boolean {
  // [RFC 5321] https://datatracker.ietf.org/doc/html/rfc5321
  const MAX_EMAIL_LENGTH = 254;
  const isInvalidInput = !email ||
    email.length === 0 ||
    email.length > MAX_EMAIL_LENGTH;

  if (isInvalidInput) return false;

  const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  return emailRegex.test(email);
}

Usage example

// Valid cases ✅ 
console.log(isValidEmail('user@example.com'));
console.log(isValidEmail('multiple@dots.co.uk'));
console.log(isValidEmail('name+tag@example.com'));

// Invalid cases ❌ 
console.log(isValidEmail('')); // - empty string 
console.log(isValidEmail(null as any)); // false - null input 
console.log(isValidEmail(undefined as any)); // false - undefined input 
console.log(isValidEmail('a'.repeat(255))); // false - exceeds max length (RFC 5321) 
console.log(isValidEmail('invalid.email@com')); // false - incomplete domain 
console.log(isValidEmail('no@dots')); // false - missing TLD 
console.log(isValidEmail('spaces in@email.com')); // false - contains spaces