docs.sheetjs.com/docz/static/electron/main.js

/* sheetjs (C) 2013-present SheetJS -- https://sheetjs.com */
var electron = require('electron');
var XLSX = require('xlsx');
var app = electron.app;
require('@electron/remote/main').initialize(); // required for Electron 14+

var win = null;

const EXT_REGEX = /\.(xls|xlsx|xlsm|xlsb|xml|csv|txt|dif|sylk|slk|prn|ods|fods|htm|html|numbers)$/i;
const pendingPaths = [];        // any paths that arrive before the window exists


// send file opening events to renderer
function sendToRenderer(filePath) {
  if (win && win.webContents) {
    win.webContents.send('file-opened', filePath);
  } else {
    pendingPaths.push(filePath);
  }
}

function firstSpreadsheetFromArgv() {
  const args = process.defaultApp             // dev: electron .
               ? process.argv.slice(2)        // skip electron executable & dir
               : process.argv.slice(1);       // skip packaged exe
  return args.find(a => EXT_REGEX.test(a));      // undefined if none
}

/* ---- single-instance guard (needed for Windows / Linux) ---- */
// on windows and linux, opening a file opens a new instance of the app, this prevents that.
// https://www.electronjs.org/docs/latest/api/app#event-second-instance
const gotLock = app.requestSingleInstanceLock();
if (!gotLock) app.quit();
else {
  app.on('second-instance', (_e, argv) => {                  // emitted in *primary* instance
    const fp = argv.find(a => EXT_REGEX.test(a));
    if (fp) sendToRenderer(fp);
    if (win) { win.show(); win.focus(); }
  });
}

/* ---- platform-specific “open file” hooks (macOS) ---- */
// https://www.electronjs.org/docs/latest/api/app#event-open-file-macos
app.on('open-file', (event, fp) => {                         // macOS Dock / Finder 
  event.preventDefault();
  sendToRenderer(fp);
});
// https://www.electronjs.org/docs/latest/api/app#event-open-url-macos
app.on('open-url', (event, url) => {                         // you can add a custom protocol if you want to handle URLs
  event.preventDefault();
  sendToRenderer(url.replace('file://', ''));                // crude, adjust if you keep deep-links
});

/* ---- normal start-up, harvest argv (Windows & Linux) ---- */
app.whenReady().then(() => {
  const fp = firstSpreadsheetFromArgv();  // Windows & Linux first launch
  if (fp) pendingPaths.push(fp);
  createWindow();
});

/* ---- create the window ---- */
function createWindow() {
  if (win) return;
  win = new electron.BrowserWindow({
    width: 800, height: 600,
    webPreferences: {
      worldSafeExecuteJavaScript: true, // required for Electron 12+
      contextIsolation: false, // required for Electron 12+
      nodeIntegration: true,
      enableRemoteModule: true
    }
  });
  win.loadURL("file://" + __dirname + "/index.html");
  require('@electron/remote/main').enable(win.webContents); // required for Electron 14
  if (process.env.NODE_ENV === 'development') win.webContents.openDevTools(); // only open devtools in development
  win.on('closed', function () { win = null; });
  win.webContents.once('did-finish-load', () => {
    pendingPaths.splice(0).forEach(sendToRenderer);
  });
}
if (app.setAboutPanelOptions) app.setAboutPanelOptions({ applicationName: 'sheetjs-electron', applicationVersion: "XLSX " + XLSX.version, copyright: "(C) 2017-present SheetJS LLC" });

app.on('ready', createWindow);
app.on('activate', createWindow);
app.on('window-all-closed', function () { if (process.platform !== 'darwin') app.quit(); });