Responsive Age calculator app using Semantic HTML5, CSS and JavaScript

I structured my website using semantic html5 markup. styling was done using css and its custom properties such as flexbox and css grid to position some of the elements. This project was to test my ability to implement javascript in a real project situation, hence did not implement any JS library.

Built with

• Semantic HTML5 markup
• CSS custom properties
• Flexbox
• CSS Grid
• Vanilla JavaScript
• Desktop-first workflow

Question:

• What are some of the best practises in using functions?
• I wrote my project without any JS library.
• What is the best JS library to learn first?