Why can't we just use getElementsByClassName, instead of getElementsByTagName?

You can in fact use getElementsByClassName to solve this challenge.

But one thing you seem to have misunderstood is that both the getElementsByTagName and getElementsByClassName methods requires you to use indexes to access elements.

Both of those methods returns a list of elements, even if there is only one element matching the tag / class you specified. The getElementById and querySelector methods are the only DOM selection methods that only return a single element, and therefore does not need to have an index used.

Here is a solution to this task that uses the getElementsByClassName method:

var fullName = document.getElementById("full_name");
var lastName = document.getElementsByClassName("last_name")[0];

Hey speir,

I guess it's because the teacher wants you to practice and get familiar with the getElementsByTagName method.

With classes you also need to add the index of the element you want to select though!