electron pass info from a custom protocol url to the main window before it opens

index.js

// capture any data you need from the url that opened the app 
app.on('open-url',function(e, strUrl){
    var someThingToUse = strUrl;
  });

const createWindow = () => {
  // Create the browser window.
  mainWindow = new BrowserWindow({
    width: 1280,
    height: 800,
  });

  mainWindow.loadURL(`file://${__dirname}/index.html?`+someThingToUse);
}