Send sync message from IpcMain to IpcRenderer - Electron

Question

In electron, It is possible to send sync message from IpcRenderer to IpcMain via ipcRenderer.sendSync('synchronous-message', 'ping').

Also possible to send async message from IpcMain to IpcRenderer using window.webContents.send('ping', 'whoooooooh!')

but is there any way to send sync message from IpcMain to IpcRenderer?

Answer 1

There is no such functionality of ipcMain ^*. However, you can achieve almost the same result asynchronously with the following steps:

• Place your code which you would run only after the synchronous call in an ipcMain callback.
• Reply to ipc message in renderer process with the result using event.sender.send

A dummy example of sum using this approach looks like the following:

main.js

const {app, BrowserWindow, ipcMain} = require('electron')
const path = require('path')

app.once('ready', () => {
  let win = new BrowserWindow()
  // have to run "sync", that is only after result is ready
  const doJobWithResult = (res) => {
    console.log(res)
  }
  win.webContents.once('dom-ready', () => {
    win.webContents
    .send('sum-request', 23, 98, 3, 61)
    ipcMain.once('sum-reply', (event, sum) => {
      doJobWithResult(sum)
    })
  })
  win.loadURL(path.resolve(__dirname, 'test.html'))
})

renderer.js (referred from test.html)

const {ipcRenderer} = require('electron')

window.onload = () => {
  const add = (a, b) => {
    return a + b
  }
  ipcRenderer.on('sum-request', (event, ...args) => {
    event.sender.send('sum-reply', [...args].reduce(add, 0))
  })
}

---

_{* I suppose it's because calling synchronously from main to renderer would block the main nodejs process which does serve renderer processes too after all.}

Answer 2

The easiest way to access Main Process Objects in renderer process(sync)

// In renderer process (web page).
const { ipcRenderer } = require('electron');
let exec = eval => ipcRenderer.sendSync('synchronous-message', eval);
exec("win.setSize(500,500)");
console.log(exec("win.getBounds()"));
console.log(exec("app.getVersion()"));

// In the Main process.
ipcMain.on('synchronous-message', (event, arg) => {
  event.returnValue = eval(arg);
})

It's the way to send msg from Main process to renderer process.(Official example)

// In renderer process (web page).
ipcRenderer.on('test', (event, arg) => {
    console.log(arg) // 123
})
// In the Main process.(after loaded you can send msg to renderer process)
win.webContents.on('did-finish-load', () => {
    win.webContents.send('test',123);
})