Mortgage repayment form solution using pure CSS and JS

What are you most proud of, and what would you do differently next time?

I'm proud of completing this challenge and making it look as close as I could make it look to the original. I'm proud of adding the form validation as well as form functionality using javascript.

What specific areas of your project would you like help with?

I would like a review of my javascript code and a review of the best practices that I tried to use in the building of this form