Minimum eight characters, at least one letter and one number:
/^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$/
Minimum eight characters, at least one letter, one number and one special character:
/^(?=.*[A-Za-z])(?=.*\d)(?=.*[@$!%*#?&])[A-Za-z\d@$!%*#?&]{8,}$/
Minimum eight characters, at least one uppercase letter, one lowercase letter and one number: