Electron: Cannot read property 'send' of u

Question

I'm trying to read the files from a directory using the fs module, and display that in a div with the id displayfiles in an Electron app. I keep getting the error :

 Cannot read property 'send' of undefined

Here is my renderer.js

// This file is required by the index.html file and will
// be executed in the renderer process for that window.
// All of the Node.js APIs are available in this process.
const electron = require('electron');
const dialog = electron.dialog;
const fs = require('fs');
const remote = require ("electron").remote;
const ipcRenderer = electron.ipcRenderer;
const template=[
    {
        label: 'File',
        submenu: [
            {
                label:'Open USB',
                click () { dialog.showOpenDialog( {
                    properties: ['openDirectory']
                },directorySelectorCallback)

                }
            },
            {
                label:'Exit',
                click() {

                }
            },
        ]
    },
    {
        label: 'Edit',
        submenu: [
            {role: 'undo'},
            {role: 'redo'},
            {type: 'separator'},
            {role: 'cut'},
            {role: 'copy'},
            {role: 'paste'},
            {role: 'pasteandmatchstyle'},
            {role: 'delete'},
            {role: 'selectall'}
        ]
    },
    {
        label: 'View',
        submenu: [
            {role: 'reload'},
            {role: 'forcereload'},
            {role: 'toggledevtools'},
            {type: 'separator'},
            {role: 'resetzoom'},
            {role: 'zoomin'},
            {role: 'zoomout'},
            {type: 'separator'},
            {role: 'togglefullscreen'}
        ]
    },
    {
        role: 'window',
        submenu: [
            {role: 'minimize'},
            {role: 'close'}
        ]
    },
]

function directorySelectorCallback(filenames) {
    if (filenames && filenames.length > 0) {
        console.log(filenames[0]);
        fs.readdir(filenames[0], (err, files) => {
            'use strict';
            if (err) throw  err;
            //the files parameter is an array of the files and folders in the path we passed. So we loop through the array, printing each file and folder
            for (let file of files) {
                console.log(file);
                ipcRenderer.send('add-file', 'an-document.getElementById(\'display-files\').innerHTML += `<li>${file}</li>`;')

            }
        });
    }
}
module.exports.template=template;

Here is my code for main.js:

// Modules to control application life and create native browser window
const electron = require('electron')
const {app, BrowserWindow,Menu,ipcMain} = require('electron')
const menuTemplate=require('./renderer.js').template
// 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.
var mainWindow=null;

function createWindow () {
  // Create the browser window.
  mainWindow = new BrowserWindow({width: 800, height: 600,icon: __dirname + '/Rexnord.ico'})

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

  // Open the DevTools.
   mainWindow.webContents.openDevTools()
  // Emitted when the window is closed.
  mainWindow.on('closed', function () {
    // 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.
    mainWindow = null
  })
    let menu = Menu.buildFromTemplate(menuTemplate)
    Menu.setApplicationMenu(menu);
}
ipcMain.on('add-file', (event, arg)=> {
   mainWindow.webContents.executeJavaScript(arg);
})
// 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', function () {
  // 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', function () {
  // 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 (mainWindow === 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.

Im trying to to the ipc modules to communicate between the renderer.js and the main.js file. From what I read, I should be able to the ipcrenderer module to send a message to the main process via a channel but I kept getting this error. Can someone tell me what I'm doing wrong?

Answer 1

Your problem is that you require(./renderer) from Main process.

• It's necessary because Menu is a Main process module
• OTOH ipcRenderer is not defined in Main process, thus won't be available in the callback either

You should re-structure your code, to not use renderer.js both from Main and Renderer.

Since you send message to Main only to execute code in Renderer, you can simply setup a listener on ipcRenderer to manipulate DOM and do everything else in Main process (click's arguments make this easy).

main.js

const { app, BrowserWindow, Menu } = require('electron')
const path = require('path')
const { menuTemplate } = require('./template')

app.once('ready', () => {
  let win = new BrowserWindow()
  win.loadURL(path.join(__dirname, '/index.html'))

  let menu = Menu.buildFromTemplate(menuTemplate)
  Menu.setApplicationMenu(menu)
})

template.js

const { dialog } = require('electron')
const fs = require('fs')

module.exports = {
  menuTemplate: [
    {
      label: 'File',
      submenu: [
        {
          label: 'Open USB',
          click (menuItem, browserWindow, event) {
            dialog.showOpenDialog({
              properties: ['openDirectory']
            }, ([dir]) => {
              try {
                if (fs.statSync(dir).isDirectory()) {
                  const files = fs.readdirSync(dir)
                  browserWindow.webContents.send('add-file', files)
                }
              } catch (err) {
                console.error(err)
              }
            })
          }
        }
      ]
    }
  ]
}

index.html

<html>
  <body>
    <script>
      const { ipcRenderer } = require('electron')
      ipcRenderer.on('add-file', (event, files) => {
        files.forEach(f => {
          document.getElementById('display-files').innerHTML +=
            `<li>${f}</li>`
        })
      })
    </script>
    <div id='display-files'>
      Files:
    </div>
  </body>
</html>