Intro component with sign-up form || CSS-Grid, Vanilla JS

There are a lot of new things I'd learned throughout this challenge.

• Floating labels
• Dom Manipulation
• Form validation
• Form Data Process
• Passing a function as an argument
• Refactoring code.

In this case, when I clicked the submit button and all inputs are empty, I wanted the first error message to appear are "First Name is required", instead of "First Name at least 5 characters". So I remember we can pass a function as an argument, right? Then I create another statement inside a checkRequired() then pass a checkLenght() and checkEmail() as an argument, and it works as I wanted.

My question is, can you guys explain why it is working? I really didn't know what I'm doing I just intuitively pass that function into an else if statement but I really don't understand how it works.

Your feedback will be really appreciated guys.Thanks.