How do i create a DOM element without reloading the page (using js, node, and express)?

Hi. I have 2 questions; 1 : How do i create a DOM element without reloading the page? I am working on a big project with a few friends, a designer and one who makes HTML and CSS. I do the front-end JS, and back-end node. I need to create elements in the page without reloading, because it will have to reload A LOT of times, and i've seen how annoying that can be.

2: How do i completely hide my source code? (I have googled it and it said two things: 1: Remove the ".map" files. I dont have any .map files, or 2: Encrypt your code, but it said that if people try, they can decrypt it.) I want it 100% guaranteed that nobody can see my source code, because i have my own custom encryption system on a js file, and when i import it in a client side js file, it shows everything on the clients browser.

If 2 is impossible, how can I make a get request to a route via fetch() on client-side to encrypt the data i send it, and then send it back encrypted? The problem is that i want it to be secured, so nobody else can send a request to it.

I apologize if this is too much, but i have a limited time to finish this project.

Thank you, Glaukio