Why do we need var message = ''; at the beginning of the code?

Hi there! JavaScript is pretty smart. In many languages you have to explicitly say what kind of data a variable is going to hold before you can even use it. JavaScript has something it calls "type inference" where it makes a best guess as to what the data type is by how you use it. My advice is to run this in the console and take a look at what it tells you:

var message1;
var message2 = '';
message1 += 2;
message2 += 2;
console.log(message1);
console.log(message2);

In this example, we declare a variable named message1. Because we don't iniitialize with a number or a string or anything else, JS says that it is of type "undefined". And it's right. We haven't yet put anything in that variable so it has no idea what it's supposed to contain. In the message2 variable we start by initializing it as an empty string. So JavaScript knows that even though there currently are no characters in that string, it will later hold a string. So when we do the concatenation with the 2, it understands we want a string and magically converts it for us!

It's always a good idea to initialize something you know will contain a string later with an empty string to start with. As you can see there can be unexpected consequences with concatenation later on down the road if this is not done.

Hope this helps!