How do you use the process option?

[Jakobud]

I'm using curlrequest to fetch some remote files from a web server and save them locally (using curl's "output" option). If the response is a 404, it saves the 404 HTML page as the local file.

How can I do things like check the response before taking action? I'm seeing the process option but not sure how to use it. I tried this:

let options = {
  ...
  process: res => {
    console.log(res)
  }
}

but that didn't seem to do anything. It says you pass a function. Not sure.

Is it possible to do what I want?