Predict and solve 2.js in debug

Author: habohlin

Sprint-3/2-mandatory-debug/2.js

@@ -2,7 +2,11 @@
 
 // Predict the output of the following code:
 // =============> Write your prediction here
+// Answer: I believe that when we run the code we will get a Reference Error, because we are trying to
+// call a function getLastDigit with an argument even though the function doesn't have any parameters.
+// Or possibly the error might reference num in the function body being undefined.
 
+/*
 const num = 103;
 
 function getLastDigit() {
@@ -12,13 +16,46 @@ function getLastDigit() {
 console.log(`The last digit of 42 is ${getLastDigit(42)}`);
 console.log(`The last digit of 105 is ${getLastDigit(105)}`);
 console.log(`The last digit of 806 is ${getLastDigit(806)}`);
+*/
 
 // Now run the code and compare the output to your prediction
 // =============> write the output here
+// The last digit of 42 is 3
+// The last digit of 105 is 3
+// The last digit of 806 is 3
+
 // Explain why the output is the way it is
 // =============> write your explanation here
+// Answer: I was wrong, there was no error message. Instead
+// The last digit of 42 is 3
+// The last digit of 105 is 3
+// The last digit of 806 is 3
+// was logged to the console. There was no Reference Error about num being undefined in the function body
+// because num IS defined, just above the function and has global scope, so it is reachable by the function.
+// Also, no error was thrown due to calling the function with arguments even though it accepted no parameters.
+// This is because JavaScript is a dynamic/forgiving language that rather removes surplus information and keeps
+// executing the code than stops it and gives an error message. So any surplus arguments passed into a function
+// call just gets ignored. That is why the passed arguments have no effect on the function's return value.
+// To make them have effect, I will add a parameter to the function, and call it num. Then when num gets accessed
+// in the function body, it will not be the value of the global num, but instead the function-local parameter
+// num.
+
 // Finally, correct the code to fix the problem
 // =============> write your new code here
 
+const num = 103;
+
+function getLastDigit(num) {
+  return num.toString().slice(-1);
+}
+
+console.log(`The last digit of 42 is ${getLastDigit(42)}`);
+console.log(`The last digit of 105 is ${getLastDigit(105)}`);
+console.log(`The last digit of 806 is ${getLastDigit(806)}`);
+
 // This program should tell the user the last digit of each number.
 // Explain why getLastDigit is not working properly - correct the problem
+// Answer: now it works as expected
+// The last digit of 42 is 2
+// The last digit of 105 is 5
+// The last digit of 806 is 6