JSFiddle - React, Tailwind, and code Playground

JavaScript

function cev(email) 
{
 if (/(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])/.test(email))
  {
    if(email.indexOf("..") == -1){
        return email + ": valid";
    }
  }
    return email + ": not valid";
}






console.log("valid");
console.log(cev("firstname+lastname@example.com"));
console.log(cev("email@example.museum"));
console.log(cev("firstname-lastname@example.com"));
console.log(cev("email@123.123.123.123"));
console.log("invalid");

console.log(cev("#@%^%#$@#$@#.com"));
console.log(cev("email@-example.com"));
console.log(cev("email@example..com"));
console.log(cev("Abc..123@example.com"));
console.log(cev("email..email@example.com"));