fix(sprint-1): resolve ReferenceError by declaring variable before use

Author: Tarawally

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

@@ -1,9 +1,16 @@
-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
+
+// TypeError: cardNumber.slice is not a function - .slice() exists on strings, not numbers
+// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice
+
+// Solution:
+const cardNumber = 4533787178994213;
+const last4Digits = String(cardNumber).slice(-4);