Mask a portion of a String using RegExp

Question

I'm trying to mask a portion of a string using JavaScript.

e.g. Mask second and third segment of credit-card number like this using regex:

• 4567 6365 7987 3783 → 4567 **** **** 3783
• 3457 732837 82372 → 3457 ****** 82372

I just want to keep the first 4 numbers and the last 5 characters.

This is my first attempt: /(?!^.*)[^a-zA-Z\s](?=.{5})/g

https://regex101.com/r/ZBi54c/2

Answer 1

You can try this:

var cardnumber = '4567 6365 7987 3783';
var first4 = cardnumber.substring(0, 4);
var last5 = cardnumber.substring(cardnumber.length - 5);

mask = cardnumber.substring(4, cardnumber.length - 5).replace(/\d/g,"*");
console.log(first4 + mask + last5);

Answer 2

You could slice the first four digits and apply a replacement for the rest.

console.log(
    ['4567 6365 7987 3783', '3457 732837 82372'].map(
        s => s.slice(0, 4) + s.slice(4).replace(/\d(?=.* )/g, '*')
    )
);