const regex = /^(([^<>()\[\]\.,;:\s@\"]+(\.[^<>()\[\]\.,;:\s@\"]+)*)|(\".+\"))@(([^<>()[\]\.,;:\s@\"]+\.)+[^<>()[\]\.,;:\s@\"]{2,})/gim;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('^(([^<>()\\[\\]\\.,;:\\s@\\"]+(\\.[^<>()\\[\\]\\.,;:\\s@\\"]+)*)|(\\".+\\"))@(([^<>()[\\]\\.,;:\\s@\\"]+\\.)+[^<>()[\\]\\.,;:\\s@\\"]{2,})', 'gim')
const str = `prettyandsimple@example.com
very.common@example.com
disposable.style.email.with+symbol@example.com
other.email-with-dash@example.com
x@example.com (one-letter local part)
"much.more unusual"@example.com
"very.unusual.@.unusual.com"@example.com
"very.(),:;<>[]\\".VERY.\\"very@\\\\ \\"very\\".unusual"@strange.example.com
example-indeed@strange-example.com
admin@mailserver1 (local domain name with no TLD)
#!\$%&'*+-/=?^_\`{}|~@example.org
"()<>[]:,;@\\\\\\"!#\$%&'*+-/=?^_\`{}| ~.a"@example.org
" "@example.org (space between the quotes)
example@localhost (sent from localhost)
example@s.solutions (see the List of Internet top-level domains)
user@com
user@localserver
user@[IPv6:2001:db8::1]
©other.email-with-dash@example.com
?prettyandsimple@example.com
Invalid email addresses[edit]
Abc.example.com (no @ character)
A@b@c@example.com (only one @ is allowed outside quotation marks)
a"b(c)d,e:f;g<h>i[j\\k]l@example.com (none of the special characters in this local part are allowed outside quotation marks)
just"not"right@example.com (quoted strings must be dot separated or the only element making up the local part)
this is"not\\allowed@example.com (spaces, quotes, and backslashes may only exist when within quoted strings and preceded by a backslash)
this\\ still\\"not\\\\allowed@example.com (even if escaped (preceded by a backslash), spaces, quotes, and backslashes must still be contained by quotes)
john..doe@example.com (double dot before @)
with caveat: Gmail lets this through, Email address#Local-part the dots altogether
john.doe@example..com (double dot after @)`;
const subst = `QuestionText = "$1",`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions