Regular expressions, or regex, refer to encoded text strings designed to match patterns in other strings.
These are helpful when you need to find a string of characters that match a type of pattern.
These patterns can be simple, very complex.
One of the more common ones is for email address validation.

			
					function validate(input) {
  let mailformat = /^[a-zA-Z0-9.!#$%&’*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:.[a-zA-Z0-9-]+)*$/
  if (mailformat.test(String(input).toLowerCase())) {
    console.log("Hey , Mail is Correct")

  } else {
    console.log("This is not a valid email address");
  }
}

validate('s@gmail.com')
// Hey , Mail is Correct
validate('sgmailcom')
// This is not a valid email address

An email is a string (a subset of ASCII characters) separated into two parts by the @ symbol.
A "email name" and a domain, that is mailName@domain.
The length of the email name part may be up to 64 characters long, and the domain name may be up to 253 characters.

Email Regex for validating email.