CreditCardEncryption.js

        function encrypt(str, num) {
           let len = str.substring(num, str.length - num).length;
            let goin = '*'.repeat(len);
            let res =  str.slice(0, num) + goin + str.slice(str.length - num);
           return res;
        }

        console.log(encrypt('111111111111111111111111111', 4)); // 1111*******************1111