In a main window, when a button is clicked, the second/child window will popped up via an ipc call.
This works when open the pop window on the first time. If I closed the pop window and reopen it again, I will get this error:

Uncaught Exception: Error: Object has been destroyed at Error (native)
at EventEmitter. (/home/xxxx/electron/fin/main.js:36:21) at emitOne
(events.js:96:13) at EventEmitter.emit (events.js:188:7) at
EventEmitter.
(/home/xxxx/electron/fin/node_modules/electron-prebuilt/dist/resources/electron.asar/browser/api/web-contents.js:156:13)
at emitTwo (events.js:106:13) at EventEmitter.emit (events.js:191:7)

#main.js on app ready:

mainWindow = new BrowserWindow({width: 800, height: 600})





  mainWindow.loadURL(`file://${__dirname}/index.html`)





  mainWindow.webContents.openDevTools()





  mainWindow.on('closed', function () {



    mainWindow = null

  })



  let popWindow = new BrowserWindow({parent: mainWindow, width: 450, height: 450, show: false});

  popWindow.loadURL(`file://${__dirname}/app/pop.html`);

  popWindow.webContents.openDevTools();



  ipc.on('toggle-popwindow', function(){

         popWindow.show();    

  });

And when I add hide() in the 'closed' method:

popWindow.on('closed', function (event) {

popWindow.hide();

});

I get this:

Uncaught Exception:

Error: Object has been destroyed

What is the problem?