3.js

const cardNumber = 4533787178994213;
const last4Digits = cardNumber.toString().slice(-4);

console.log(last4Digits); // should print 4213

// The last4Digits variable should store the last 4 digits of cardNumber
// However, the code isn't working
// Before running the code, make and explain a prediction about why the code won't work
// Then run the code and see what error it gives.
// Consider: Why does it give this error? Is this what I predicted? If not, what's different?
// Then try updating the expression last4Digits is assigned to, in order to get the correct value


// Before running the code, I predicted: The code will throw an error because cardNumber is defined as a number (not a string), and numbers don't have a .slice() method.
// The .slice() method is only available on strings and arrays, not on number primitives
// To fix the code, we need to convert the number to a string first, then use .slice()