main.js

const { app, BrowserWindow } = require("electron"),
  path = require("path"),
  url = require("url");

const {
  default: installExtension,
  REACT_DEVELOPER_TOOLS
} = require("electron-devtools-installer");

let mainWindow;

function createWindow() {
  mainWindow = new BrowserWindow({
    width: 1000,
    height: 600,
    frame: false
  });
  mainWindow.loadURL(
    url.format({
      pathname: path.join(__dirname, "index.html"),
      protocol: "file:",
      slashes: true
    })
  );

  installExtension(REACT_DEVELOPER_TOOLS)
    .then(name => console.log(`Add Extension: ${name}`))
    .catch(err => console.log(`An error occurred: ${err}`));

  mainWindow.on("closed", () => {
    mainWindow = null;
  });
}

app.on("ready", createWindow);

app.on("window-all-closed", () => {
  // quit app when it's not OS X
  if (process.platform !== "darwin") {
    app.quit();
  }
});

// Reactivate a window in OS X
app.on("activate", () => {
  if (mainWindow === null) {
    createWindow();
  }
});