Partial demo of credit card check using Regex and luhnCheck methods

partial_fieldValidator2.js

const validateCardNumber = (number) => {
	var regex = new RegExp("^[0-9]{16}$");
	if (!regex.test(number)) { return false; }

	return luhnCheck(number);
}

const luhnCheck = (val) => {
	var sum = 0;
	for (var i = 0; i < val.length; i++) {
		var intVal = parseInt(val.substr(i, 1));
		if (i % 2 === 0) {
			intVal *= 2;
			if (intVal > 9) {
				intVal = 1 + (intVal % 10);
			}
		}
		sum += intVal;
	}
	return (sum % 10) === 0;
}