function getNationalSignificantNumberDigits(number, country, metadata) {
	// Create "as you type" formatter.
	const formatter = new AsYouType(country, metadata)
	// Input partial national phone number.
	formatter.input(number)
	// Return the parsed partial national phone number.
	const phoneNumber = formatter.getNumber()
	return phoneNumber && phoneNumber.nationalNumber
}
Parses a partially entered national phone number digits
(or a partially entered E.164 international phone number)
and returns the national significant number part.
National significant number returned doesn't come with a national prefix.
@param {string} number - National number digits. Or possibly incomplete E.164 phone number.
@param {string?} country
@param {object} metadata - `libphonenumber-js` metadata.
@return {string} [result]