How exactly add "Service-Worker-Allowed" to register service worker scope in upper folder

Ok... I was a little confused, and even now I guess I have to get deep in the facts and study http headers better...

Anyway as stated in many questions & answer on stackoverflow, it's not possible to alter headers during http request, unless it's not an ajax request (and that's not this case).

now on this post Understanding Service Worker scope for a similar question @Ashraf Sabry answered he could alter the headers using web.config file of IIS Web Server. --> So finally I understood that the header to add is a response header, but before the response is interpreted by the browser --> As stated here https://docs.microsoft.com/en-us/iis/configuration/system.webserver/httpprotocol/customheaders/ that configuration is for response header.

I guess there is not clear way to control that header to make service worker doing his work in a subfolder using html/javascript... It's a problem that could be solved only with server configurations.

A was doing my tests on Node, for didactical porpouse I tried to write a simple http server to test this issue starting from this tutorial https://ilovecoding.org/lessons/create-a-simple-http-server-with-nodejs

the result is here (a "server.js" file runned on Node):

var http = require('http');
var url = require('url');
var querystring = require('querystring');
var fs = require('fs');

http.createServer(function(request, response){
    pathName = url.parse(request.url).pathname;
    console.log(pathName);
    fs.readFile(__dirname + pathName, function(err, data){
        if(err){
            response.writeHead(404, {'Content-type':'text/plan'});
            response.write('Page Was Not Found');
            response.end();
        }
        else{
            if(pathName.endsWith(".html")){
                //response.writeHead(200, {'Service-Worker-Allowed':'/', 'Content-Type':'text/html'});
                response.writeHead(200, {'Content-Type':'text/html'});
                console.log("serving html");
            }
            else if(pathName.endsWith(".js")){
                response.writeHead(200, {'Service-Worker-Allowed':'/', 'Content-Type':'application/javascript'});
                //response.writeHead(200, {'Content-Type':'text/javascript'});
                console.log("serving js");
            }
            else if(pathName.endsWith(".css")){
                //response.writeHead(200, {'Service-Worker-Allowed':'/', 'Content-Type':'text/css'});
                response.writeHead(200, {'Content-Type':'text/css'});
                console.log("serving css");
            }
            else{
                response.writeHead(200);
                console.log("serving other");
            }
            response.write(data);
            response.end();
        }
    })
}).listen(8080);

Using this js Node Server I could reach the same result stated for settings in IIS in the above link.

Note that after some test with this js, I reached that the file which needs "Service-Worker-Allowed:/" is the app.js file.

Now the application work as wanted returning no error. As final prove tracing requests on fiddler I can clearly see the initial request for app.js, with "Service-Worker-Allowed: /" in the response;

My conclusion is that not always it is possible to handle server configuration, so putting service worker file on root folder of the app is the best approach.

Hope this could be helpful for some others...