I made my take on porting Google's into javascirpt and seems that it's doable.
The resulting library does everything a modern web application needs while maintaining a much smaller size of about 110 kilobytes.
Speaking of phone number extensions, I myself consider them obsolete and I'd just discard the extension part given we're in the 21st century.
This not only creates a standardized string that can be later used in a comparison or stored in a database, but also ensures that the data that is received on the server end contains only the expected data.
This is important because most website attacks are caused by accepting user input blindly.
Often times we can give our users an example and they will still enter the wrong format.