How to change native menu of electron-quick-start example app

It looks like the electron Menu and MenuItem objects are set up to be immutable.

This means if you want to modify them, you have to create new objects and use that instead. This is what my code does for this, to hide the help menu and developer tools:

// main.js

function createWindow () {
  // Create the browser window.
  mainWindow = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      preload: path.join(__dirname, 'preload.js')
    }
  })

...

  let defaultMenu = Menu.getApplicationMenu()

  let newMenu = new Menu();
  defaultMenu.items
    .filter(x => x.role != 'help')
    .forEach(x => {
      if(x.role == 'viewmenu' && process.env.NODE_ENV == 'production') {
        let newSubmenu = new Menu();

        x.submenu.items.filter(y => y.role != 'toggledevtools').forEach(y => newSubmenu.append(y));

        x.submenu = newSubmenu;

        newMenu.append(
          new MenuItem({
            type: x.type,
            label: x.label,
            submenu: newSubmenu
          })
        );
      } else {
        newMenu.append(x);
      }
    })

  Menu.setApplicationMenu(newMenu);

...
  })
}

app.on('ready', createWindow)

Put your logic to customise the menu into your app('ready') event callback. Give try to following code example

const {app, BrowserWindow, Menu} = require('electron');
let mainWindow;
let menuTemplate = [
    {
        label: "Window Manager",
        submenu: [
            { label: "create New" }
        ]
    },
    {
      label : "View",
            submenu : [
        { role : "reload" },
        { label : "custom reload" }
        ]
    }
];
function appInit () {
  // Create the browser window.
  mainWindow = new BrowserWindow({width: 800, height: 600})

  // and load the main.html of the app.
  mainWindow.loadFile('main.html')

    let menu = Menu.buildFromTemplate(menuTemplate);
    Menu.setApplicationMenu(menu);
}
app.on('ready', () => {
  appInit();
})

Electron's 'default_app' sets the menu; if you want to avoid this, you need Electron to start your app directly not via the default app (note: if you start your app with something like electron . you actually start the default app).

Electron looks in its resource folder for 'app', 'app.asar' or 'default_app', so in order to start your app directly you need to either copy or link it into Electron's resource folder.

Regardless of how you start your app, you can set your menu using Menu.setApplicationMenu -- you can do it in the main process, you don't need to do it in the Renderer like in your example. Incidentally, there is a typo in your main.html (requier instead of require) so if that's your actual code it would indicate that your main.js does not run at all.