added solution to 3.js

Author: Alex Jamshidi

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

@@ -1,9 +1,21 @@
 const cardNumber = 4533787178994213;
-const last4Digits = cardNumber.slice(-4);
+const last4Digits = String(cardNumber).slice(-4);
+
+console.log(last4Digits)
 
 // 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
+
+// .slice needs to act on a string not a number, so I would expect something like 'incorrect input' as an error
+
 // 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?
+
+// TypeError: cardNumber.slice is not a function
+// This is not exactly the words I expected the error to say but is correctly identifying the same error
+// I think it is saying that cardNumber.slice is not a function of a number, hence the TypeError
+
 // Then try updating the expression last4Digits is assigned to, in order to get the correct value
+
+// I converted cardNumber to a string and error resolved and it return the correct output