NodeJS v8.10.0 also backtracks on regexen: insert a space in the email address at the beginning or middle and it will be a bit slow. insert space at end and it will be very slow...

regex-done-right.mjs

#!/usr/bin/node --experimental-modules

// fetch the dependency with: yarn add re2
// I tested with [email protected]
import RE2 from "re2";

const emailRegex = new RE2("^[A-Za-z0-9_%+-](\.?[A-Za-z0-9_%+-]+)+@[A-Za-z0-9-](\.?[A-Za-z0-9-]+)+\.[A-Za-z]{2,6}$");

console.log("This is fine: " + emailRegex.test("robert.jack.frederic.manfred.otto.hermann.luis.egon.erwin@friday.de"));

console.log("This is false, but still fast: " + emailRegex.test("robert.jack.frederic.manfred.otto.hermann.luis.egon.erwin@friday .de"))

regex-test.js

#!/usr/bin/node

// this regex causes a freeze when run via TypeScript and some Webpack transpiling stuff in the browser
// still need to figure out why, but it's quite reassuring that NodeJS doesn't have this problem!

const emailRegex = /^[A-Za-z0-9_%+-](\.?[A-Za-z0-9_%+-]+)+@[A-Za-z0-9-](\.?[A-Za-z0-9-]+)+\.[A-Za-z]{2,6}$/;

console.log("This is fine: " + emailRegex.test("robert.jack.frederic.manfred.otto.hermann.luis.egon.erwin@friday.de"));

console.log("Does not match and is somewhat slow: ");
console.log(emailRegex.test("robert.jack.frederic.manfred.otto. [email protected]"))

console.log("Does not match and is really slow: ");
console.log(emailRegex.test("robert.jack.frederic.manfred.otto.hermann.luis.egon. [email protected]"))

console.log("This takes more time than my patience is long, so I don't know if it is shorter than a day or not:");
console.log(emailRegex.test("robert.jack.frederic.manfred.otto.hermann.luis.egon.erwin@friday .de"))