// Created on savesnippets.com · https://savesnippets.com/09hXDjHZYeB9CM
function isValidEmail(email) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(String(email).toLowerCase());
}

// Stricter RFC 5322 approximation
function isValidEmailStrict(email) {
  return /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\.[a-zA-Z]{2,}$/.test(email);
}

// Usage
console.log(isValidEmail('user@example.com'));  // true
console.log(isValidEmail('not-an-email'));       // false