main.js

const {app, BrowserWindow} = require('electron')
const path = require('path')
const fs = require('fs')
const url = require('url')
const Realm = require('realm')

const DogSchema = {
    name: 'Dog',
    properties: {
        name: 'string',
        age: 'int',
    }
};
fs.mkdirSync(`${path.resolve('.')}/realm`);

Realm.open({
    schema: [DogSchema],
    path: `${path.resolve('./realm')}/dog.realm`,
})
.then((realm) => {
    let dogs = realm.objects('Dog'); // retrieves all Dogs from the Realm
    if(dogs.length === 0) {
        try {
            realm.write(() => {
                realm.create('Dog', {
                    name: 'Bro',
                    age: 10
                });
            });
        } catch (e) {
            console.log("Error on creation");
        }
        console.log('Saved Bro');
    } else {
      console.log('Bro exists')
    }
});
  
  // Keep a global reference of the window object, if you don't, the window will
  // be closed automatically when the JavaScript object is garbage collected.
  let win
  
  function createWindow () {
    // Create the browser window.
    win = new BrowserWindow({width: 800, height: 600})
  
    // and load the index.html of the app.
    win.loadURL(url.format({
      pathname: path.join(__dirname, 'index.html'),
      protocol: 'file:',
      slashes: true
    }))
  
    // Open the DevTools.
    win.webContents.openDevTools()
  
    // Emitted when the window is closed.
    win.on('closed', () => {
      // 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', createWindow)
  
  // 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()
    }
  })
  
  // In this file you can include the rest of your app's specific main process
  // code. You can also put them in separate files and require them here.