electron/docs/api/ipc-main.md

ipcMain

The ipcMain module is an instance of the EventEmitter class. When used in the main process, it handles asynchronous and synchronous messages sent from a renderer process (web page). Messages sent from a renderer will be emitted to this module.

Sending Messages

It is also possible to send messages from the main process to the renderer process, see webContents.send for more information.

• When sending a message, the event name is the channel.
• To reply a synchronous message, you need to set event.returnValue.
• To send an asynchronous back to the sender, you can use event.sender.send(...).

An example of sending and handling messages between the render and main processes:

// In main process.
const ipcMain = require('electron').ipcMain;
ipcMain.on('asynchronous-message', function(event, arg) {
  console.log(arg);  // prints "ping"
  event.sender.send('asynchronous-reply', 'pong');
});

ipcMain.on('synchronous-message', function(event, arg) {
  console.log(arg);  // prints "ping"
  event.returnValue = 'pong';
});

// In renderer process (web page).
const ipcRenderer = require('electron').ipcRenderer;
console.log(ipcRenderer.sendSync('synchronous-message', 'ping')); // prints "pong"

ipcRenderer.on('asynchronous-reply', function(event, arg) {
  console.log(arg); // prints "pong"
});
ipcRenderer.send('asynchronous-message', 'ping');

Listening for Messages

The ipcMain module has the following method to listen for events:

ipcMain.on(channel, listener)

• channel String
• listener Function

Listens to channel, when a new message arrives listener would be called with listener(event, args...).

ipcMain.once(channel, listener)

• channel String
• listener Function

Adds a one time listener function for the event. This listener is invoked only the next time a message is sent to channel, after which it is removed.

ipcMain.removeListener(channel, listener)

• channel String
• listener Function

Removes the specified listener from the listener array for the specified channel.

ipcMain.removeAllListeners([channel])

• channel String (optional)

Removes all listeners, or those of the specified channel.

Event object

The event object passed to the callback has the following methods:

event.returnValue

Set this to the value to be returned in a synchronous message.

event.sender

Returns the webContents that sent the message, you can call event.sender.send to reply to the asynchronous message, see webContents.send for more information.