electron/docs/api/ipc-main.md

ipcMain

Communicate asynchronously from the main process to renderer processes.

Process: Main

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 to a synchronous message, you need to set event.returnValue.
• To send an asynchronous message back to the sender, you can use event.reply(...). This helper method will automatically handle messages coming from frames that aren't the main frame (e.g. iframes) whereas event.sender.send(...) will always send to the main frame.

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

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

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

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

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

Methods

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

Removes listeners of the specified channel.

Event object

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

event.frameId

An Integer representing the ID of the renderer frame that sent this message.

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.

event.reply

A function that will send an IPC message to the renderer frane that sent the original message that you are currently handling. You should use this method to "reply" to the sent message in order to guaruntee the reply will go to the correct process and frame.