unleash.unleash/src/lib/util/is-email.ts

// Email address matcher.
// eslint-disable-next-line no-useless-escape
const matcher =
    /[A-Z0-9.!#$%&'*+-/=?^_{|}~]+@[A-Z0-9][A-Z0-9.!#$%&'*+-/=?^_{|}~]*\.[A-Z]{2,}$/i;

/**
 * Loosely validate an email address.
 * Max length of an email address is 320 characters: 64 for the local part + 1 for the @ +
 * 255 for the domain part.
 * See https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.3.1.1
 *
 * Being a bit extra cautious here and limiting the max length to 500 characters, which prevents
 * [Regular expression Denial of Service - ReDoS](https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS) attacks
 * due to polynomial regular expression used on uncontrolled data.
 *
 * @param {string} string
 * @return {boolean}
 */
function isEmail(value: string): boolean {
    if (value.length > 500) return false;
    return matcher.test(value);
}

/*
 * Exports.
 */

export default isEmail;