electron/docs/api/ipc-main-process.md

ipc (main process)

The ipc module, when used in the main process, 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.
var ipc = require('ipc');
ipc.on('asynchronous-message', function(event, arg) {
  console.log(arg);  // prints "ping"
  event.sender.send('asynchronous-reply', 'pong');
});

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

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

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

Listening for Messages

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

ipc.on(channel, callback)

• channel String - The event name.
• callback Function

When the event occurs the callback is called with an event object and a message, arg.

IPC Events

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.

Event.sender.send(channel[, arg1][, arg2][, ...])

• channel String - The event name.
• arg (optional)

This sends an asynchronous message back to the render process. Optionally, there can be one or a series of arguments, arg, which can have any type.