Regex matching online but not in App Script for MMM-YYYY

This is my Regex Pattern to match Date format MMM-YYYY(Apr-23). I have checked this on Regex101 it works as expected.

(\b\d{1,2}\D{0,3})?\b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(Nov|Dec)(?:ember)?)\D?(\d{1,2}\D?)?\D?((19[7-9]\d|20\d{2})|\d{2})

I am applying the above Regex Pattern in App Script Code looks like this

function cc(){
values_ = "Increased in the month Apr-20";
const date_regex = new RegExp('(\b\d{1,2}\D{0,3})?\b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(Nov|Dec)(?:ember)?)\D?(\d{1,2}\D?)?\D?((19[7-9]\d|20\d{2})|\d{2})');
const res = date_regex.exec(values_); 
Logger.log(res); // returns null 
}

I am not sure what's wrong here? On Searching over the Internet I learnt non-capture groups don't work on GAS Would someone help me understand about non-capture group and fix this problem. Thanks in advance!!

Solution

In your scrpt, how about the following modification?

From:

const date_regex = new RegExp('(\b\d{1,2}\D{0,3})?\b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(Nov|Dec)(?:ember)?)\D?(\d{1,2}\D?)?\D?((19[7-9]\d|20\d{2})|\d{2})');

To:

const date_regex = /(\b\d{1,2}\D{0,3})?\b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(Nov|Dec)(?:ember)?)\D?(\d{1,2}\D?)?\D?((19[7-9]\d|20\d{2})|\d{2})/;

or, if you want to use new RegExp, how about the following modification?

const date_regex = new RegExp("(\\b\\d{1,2}\\D{0,3})?\\b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|(Nov|Dec)(?:ember)?)\\D?(\\d{1,2}\\D?)?\\D?((19[7-9]\\d|20\\d{2})|\\d{2})");

When this modification is reflected in your script, [Apr-20, null, null, null, 20, null] is shown in the log.