Extracting the last 4 digits and display it

Author: carlosyabreu

Sprint-1/2-mandatory-errors/3.js

@@ -1,9 +1,34 @@
-const cardNumber = 4533787178994213;
-const last4Digits = cardNumber.slice(-4);
+// const cardNumber = 4533787178994213;
+// const last4Digits = cardNumber.slice(-4);
 
 // 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
+
+/** 
+ *Prediction: Why won’t this code work?
+const cardNumber = 4533787178994213;
+const last4Digits = cardNumber.slice(-4);
+
+
+The issue is that .slice() is a string method, but cardNumber here is a number — not a string.
+So when the code runs, JavaScript will say something like:
+
+TypeError: cardNumber.slice is not a function
+
+That’s because .slice() only works on strings or arrays — and numbers don’t have that method.
+
+Fixing the problem
+
+To use .slice(), we need to convert the number into a string first:
+
+Now it works!
+*/
+
+const cardNumber = 4533787178994213;
+const last4Digits = cardNumber.toString().slice(-4);
+console.log(last4Digits); // "4213"
+