function maskNumberWithStarsExceptFirstSixAndLastFour(cardNumber) {
const first6Digits = cardNumber.substring(0, 6);
const last4Digits = cardNumber.substring(cardNumber.length - 4);
const requiredMask = '*'.repeat(cardNumber.length - first6Digits.length - last4Digits.length);
return first6Digits + requiredMask + last4Digits;
}
const cardNumber = '8003125344656789';
const maskedNumber = maskNumberWithStarsExceptFirstSixAndLastFour(cardNumber);
console.log(maskedNumber);
/*
run:
800312******6789
*/