JSFiddle - React, Tailwind, and code Playground

JavaScript

var emailSingle = 'myname.domain.com',
    emailDouble = 'my\\.name\\.another\\.name.domain.com',
    regAt = /([^\\])\./,
    repAt = '$1@',
    regPunct = /\\./g,
    repPunct = '.';

emailSingle = emailSingle.replace(regAt, repAt).replace(regPunct, repPunct);
emailDouble = emailDouble.replace(regAt, repAt).replace(regPunct, repPunct);

alert('emailSingle: ' + emailSingle + '\nemailDouble: ' + emailDouble);