What is the name of the javascript filr when making code here

Question

I am making code.

Answer 1

I am not totally able to understand what you want to ask
so supposing that you cannot find that where to write code
You can simply add plus button on you app where all the code appears by others
then select html
there you will find js
write your code there

Answer 2

When we make a code for web it gives 3 files. css, html, js. In that is the js already connected to html

Answer 3

Yes it is already connected