I want to understand.
Javascript is a client side programming language so it's not, send nothing to server as I understand.
For example, I am uploading files from javascript, then I can immediately download them from the server without refreshing the page, How it's saving the files there if it's used only client side?

And how the comments on some websites are published without page refreshing (I come from the PHP scripting world) So I just confused.

Just understanding the question.
Thank for help anyway?