This is a simple JavaScript function that will mask your email address following this pattern:

• If it’s not an email, the input string will be returned without modification.
• If the first part of the email is shorter than 4 characters, the entire username will be masked (me@example.com => *@e*****e.com)
• If the domain part of the email is shorter than 4 symbols, the entire domain will be masked
  (username@abc.com => u******e@***.com
• The TLD part (.com/.net/.org and etc) is never masked
• If the input string contains multiple emails (for example the whole log message from the server), all email addresses found in the string will be processed.

/**
 * Mask email address with asterisks to comply GDPR
 * john.doe@example.com => j******e@e****e.com
 * @param {string} emailAddress email address
 * @returns {string} masked email address
 */
function maskEmailAddress (emailAddress) {
	function mask(str) {
		var strLen = str.length;
		if (strLen > 4) {
			return str.substr(0, 1) + str.substr(1, strLen - 1).replace(/\w/g, '*') + str.substr(-1,1);
		} 
		return str.replace(/\w/g, '*');
	}
	return emailAddress.replace(/([\w.]+)@([\w.]+)(\.[\w.]+)/g, function (m, p1, p2, p3) {		
		return mask(p1) + '@' + mask(p2) + p3;
	});
	
	return emailAddress;
}

return maskEmailAddress('random string username@example.com test');