React Native and AWS Amplify Tutorial Docs.

validation.js

export function validateEmail(email) {
  if (!/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/.test(email)) {
    return 'Enter a valid email address!';
  } else return null;
}

export function validatePassword(password) {
  if (
    !/(?=(.*[0-9]))((?=.*[A-Za-z0-9])(?=.*[A-Z])(?=.*[a-z]))^.{8,}$/i.test(
      password,
    )
  ) {
    return 'Password should have 1 lowercase letter, 1 uppercase letter, 1 number, and be at least 8 characters long';
  } else return null;
}

export function validateUsername(username) {
  if (!/^[a-z0-9_-]{3,16}$/i.test(username)) {
    return 'Enter a user name 3 to 16 characters long';
  } else return null;
}

export function validateCode(code) {
  if (!code) {
    return 'Enter a valid codde';
  } else return null;
}

Thanks for the code, this helps me a lot