const str1 = '5';

​

console.log(str1.padStart(2, '0'));

// expected output: "05"

​

const fullNumber = '2034399002125581';

const last4Digits = fullNumber.slice(-4);

const maskedNumber = last4Digits.padStart(fullNumber.length, '*');

​

console.log(maskedNumber);

// expected output: "************5581"

​

var s = "10"

console.log(s.padStart("5", "0"))

//00010

​

console.log(s.padEnd("5", "0"))

//10000