Masking Credit Card Number using JavaScript

maskCC.js

function maskCC(number) {
    // If given parameter doesn't fall under below category, then return
    // 1. Should be numbers(Every element should be a number)
    // 2. Should be of length 16
    if(!(typeof number === 'string' && number.length === 16 && number.split('').map(Number).every(n => !isNaN(n)) )) {
        return;
    }

    return [...new Array(3).fill('****'), number.slice(-4)].join('-')
}

console.log(maskCC('1234567887654321')) // ****-****-****-4321
console.log(maskCC('aaaaaaaaaaaaaaaa')) // undefined