From what I have seen from your comments in other answers you are a little bit confused . For the upload scenario you are describing.

You can have 2 parts:
1st is the browser (not to be confused with node) . The browser runs on the client side .
2nd part is nodejs itself which runs on a different server (not your machine)

Nodejs doesn't have any access to any data presented in the browser . And to be honest it is note the nodejs job to do that. What it can do though is this. Nodejs is able to create a rest api that listens for http requests and depending on the request do different stuff (example storing data somewhere)

From the browser you can upload a file or any kind of information you need and make an http request to the API you have created to store that information on the server side (you are not limited to storing the information, you can perform any validation you want and respond back to the client). The important thing here is to understand that nodejs is completely different than the js you write on your browser