Javascript is a very important programming language. While the server side code can take some time to load this code works quickly. So there is a great value to use use Javascript code in a website to make it work faster. If you want to know how to write Javascript code, you can learn in this video:
If you want more details on how to code javascript, here is video playlist: https://www.youtube.com/watch?v=_9cuW9N0amE&list=PLGnR7Ae9qkw4IHV0so238Uz0LOFRxP6Kt
You can buy book to learn Javascript at https://www.amazon.com/Learn-HTML-CSS-Javascript-Jquery-ebook/dp/B07Z68Z4RG/ref=sr_1_3?dchild=1&keywords=ziscom&qid=1621026361&sr=8-3
If you want PDF version of book, you can get it here: https://ziscom.in/product/learn-html-css-javascript-and-jquery/
Contact for tasks in Javascript.