main.js

const {app,BrowserWindow} = require('electron')
const url = require('url')
const path = require('path')
//const remote = require('electron').remote
const dialog = require('electron').dialog
//var http = require('http');
var childProcess = require('child_process');

let win

const openFile = function() {
  //console.log('open file function')
  var files = dialog.showOpenDialog(win, {properties: ['openFile']});
  if(!files) { return; }
  var file = files[0];
  return file;
  //console.log(file);
}

function httpGet(url, portIn) {
    return new Promise(
        function (resolve, reject) {
          console.log('start req:' + url + portIn);
          /*http.get({host: url, port: portIn}, function(res) {
              //var body = '';
              console.log('http req');
              res.on('data', function(chunk) {
                console.log('data received');
                resolve(chunk);
              });
              res.on('end', function() {
                //console.log(body);
              });
              }).on('error', function(e) {
              console.log("Got error: " + e.message);
            });*/
            const request = new XMLHttpRequest();
            request.onload = function () {
                if (this.status === 200) {
                    // Success
                    resolve(this.response);
                } else {
                    // Something went wrong (404 etc.)
                    reject(new Error(this.statusText));
                }
            };
            request.onerror = function () {
                reject(new Error(
                    'HttpRequest Error: '+this.statusText));
            };
            request.open('GET', url+":"+portIn);
            request.send();
        });
}
function timeout(ms, promise) {
    return new Promise(function (resolve, reject) {
        promise.then(resolve);
        setTimeout(function () {
            reject(new Error('Timeout after '+ms+' ms'));
        }, ms);
    });
}
function delay(ms) {
    return new Promise(function (resolve, reject) {
        setTimeout(resolve, ms);
    });
}

function fGenerateApp() {
  // invoke child process (remote application)
  var invoked = false;
  var options = { stdio: [null, null, null, 'ipc'] };
  var args = [ /* ... */ ];
  var nodeJsProcess = childProcess.fork('./index.js', args, options);

  // listen for errors as they may prevent the exit event from firing
  nodeJsProcess.on('error', function (err) {
      if (invoked) return;
      invoked = true;
      if(err) throw err;
  });
  nodeJsProcess.on('message', function(data, server) {
    if(data === 'openDialog'){
        var file = openFile();
        nodeJsProcess.send(file);
    }
  });

    nodeJsProcess.stdout.on('data',function(data){
        console.log(data.toString());
    });

  createWindow(nodeJsProcess);
}

function createWindow (process) {

  // Create the browser window.
  win = new BrowserWindow({width: 1024, height: 768, title: "GadgetronControl", icon:'public/img/icon.png'})
  win.maximize();
  // Disable menu bar
  win.setMenu(null)

  // Open the DevTools.
  //win.webContents.openDevTools()

  delay(1000).then(function () { // nasty workaround -> promise request throws timeout
      win.loadURL('http://localhost:3000/');
  });

  // Emitted when the window is closed.
  win.on('closed', () => {
    process.kill();
    // Dereference the window object, usually you would store windows
    // in an array if your app supports multi windows, this is the time
    // when you should delete the corresponding element.
    win = null
  })
}

// This method will be called when Electron has finished
// initialization and is ready to create browser windows.
// Some APIs can only be used after this event occurs.
app.on('ready', fGenerateApp)

// Quit when all windows are closed.
app.on('window-all-closed', () => {
  // On macOS it is common for applications and their menu bar
  // to stay active until the user quits explicitly with Cmd + Q
  if (process.platform !== 'darwin') {
    app.quit()
  }
})

app.on('activate', () => {
  // On macOS it's common to re-create a window in the app when the
  // dock icon is clicked and there are no other windows open.
  if (win === null) {
    createWindow()
  }
})