validation

 email validation:

function validateEmail(email) {
    const re = /^(([^<>()[\]\\.,;:\s@"]+(\.[^<>()[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    return re.test(String(email).toLowerCase());
}
https://stackoverflow.com/questions/19605150/regex-for-password-must-contain-at-least-eight-characters-at-least-one-number-a
https://stackoverflow.com/questions/19605150/regex-for-password-must-contain-at-least-eight-characters-at-least-one-number-a
https://www.youtube.com/watch?v=wiQSUdJsc-I
https://en.wikipedia.org/wiki/Regular_expression

Regular Expression.
A password is considered valid if all the following constraints are satisfied:
It contains at least 8 characters and at most 20 characters.
It contains at least one digit.
It contains at least one upper case alphabet.
It contains at least one lower case alphabet.
It contains at least one special character which includes !@#$%&*()-+=^.
It doesn’t contain any white space.
regex = “^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&-+=()])(?=\\S+$).{8, 20}$”
where:
^ represents starting character of the string.
(?=.*[0-9]) represents a digit must occur at least once.
(?=.*[a-z]) represents a lower case alphabet must occur at least once.
(?=.*[A-Z]) represents an upper case alphabet that must occur at least once.
(?=.*[@#$%^&-+=()] represents a special character that must occur at least once.
(?=\\S+$) white spaces don’t allowed in the entire string.
.{8, 20} represents at least 8 characters and at most 20 characters.
$ represents the end of the string.