# ipcRenderer

> Communicate asynchronously from a renderer process to the main process.

Process: [Renderer](../glossary.md#renderer-process)

The `ipcRenderer` module is an  [EventEmitter][event-emitter]. It provides a few
methods so you can send synchronous and asynchronous messages from the render
process (web page) to the main process. You can also receive replies from the
main process.

See [ipcMain](ipc-main.md) for code examples.

## Methods

The `ipcRenderer` module has the following method to listen for events and send messages:

### `ipcRenderer.on(channel, listener)`

* `channel` string
* `listener` Function
  * `event` IpcRendererEvent
  * `...args` any[]

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

### `ipcRenderer.once(channel, listener)`

* `channel` string
* `listener` Function
  * `event` IpcRendererEvent
  * `...args` any[]

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.

### `ipcRenderer.removeListener(channel, listener)`

* `channel` string
* `listener` Function
  * `...args` any[]

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

### `ipcRenderer.removeAllListeners(channel)`

* `channel` string

Removes all listeners, or those of the specified `channel`.

### `ipcRenderer.send(channel, ...args)`

* `channel` string
* `...args` any[]

Send an asynchronous message to the main process via `channel`, along with
arguments. Arguments will be serialized with the [Structured Clone
Algorithm][SCA], just like [`window.postMessage`][], so prototype chains will not be
included. Sending Functions, Promises, Symbols, WeakMaps, or WeakSets will
throw an exception.

> **NOTE:** Sending non-standard JavaScript types such as DOM objects or
> special Electron objects will throw an exception.
>
> Since the main process does not have support for DOM objects such as
> `ImageBitmap`, `File`, `DOMMatrix` and so on, such objects cannot be sent over
> Electron's IPC to the main process, as the main process would have no way to decode
> them. Attempting to send such objects over IPC will result in an error.

The main process handles it by listening for `channel` with the
[`ipcMain`](ipc-main.md) module.

If you need to transfer a [`MessagePort`][] to the main process, use [`ipcRenderer.postMessage`](#ipcrendererpostmessagechannel-message-transfer).

If you want to receive a single response from the main process, like the result of a method call, consider using [`ipcRenderer.invoke`](#ipcrendererinvokechannel-args).

### `ipcRenderer.invoke(channel, ...args)`

* `channel` string
* `...args` any[]

Returns `Promise<any>` - Resolves with the response from the main process.

Send a message to the main process via `channel` and expect a result
asynchronously. Arguments will be serialized with the [Structured Clone
Algorithm][SCA], just like [`window.postMessage`][], so prototype chains will not be
included. Sending Functions, Promises, Symbols, WeakMaps, or WeakSets will
throw an exception.

> **NOTE:** Sending non-standard JavaScript types such as DOM objects or
> special Electron objects will throw an exception.
>
> Since the main process does not have support for DOM objects such as
> `ImageBitmap`, `File`, `DOMMatrix` and so on, such objects cannot be sent over
> Electron's IPC to the main process, as the main process would have no way to decode
> them. Attempting to send such objects over IPC will result in an error.

The main process should listen for `channel` with
[`ipcMain.handle()`](ipc-main.md#ipcmainhandlechannel-listener).

For example:

```javascript
// Renderer process
ipcRenderer.invoke('some-name', someArgument).then((result) => {
  // ...
})

// Main process
ipcMain.handle('some-name', async (event, someArgument) => {
  const result = await doSomeWork(someArgument)
  return result
})
```

If you need to transfer a [`MessagePort`][] to the main process, use [`ipcRenderer.postMessage`](#ipcrendererpostmessagechannel-message-transfer).

If you do not need a response to the message, consider using [`ipcRenderer.send`](#ipcrenderersendchannel-args).

### `ipcRenderer.sendSync(channel, ...args)`

* `channel` string
* `...args` any[]

Returns `any` - The value sent back by the [`ipcMain`](ipc-main.md) handler.

Send a message to the main process via `channel` and expect a result
synchronously. Arguments will be serialized with the [Structured Clone
Algorithm][SCA], just like [`window.postMessage`][], so prototype chains will not be
included. Sending Functions, Promises, Symbols, WeakMaps, or WeakSets will
throw an exception.

> **NOTE:** Sending non-standard JavaScript types such as DOM objects or
> special Electron objects will throw an exception.
>
> Since the main process does not have support for DOM objects such as
> `ImageBitmap`, `File`, `DOMMatrix` and so on, such objects cannot be sent over
> Electron's IPC to the main process, as the main process would have no way to decode
> them. Attempting to send such objects over IPC will result in an error.

The main process handles it by listening for `channel` with [`ipcMain`](ipc-main.md) module,
and replies by setting `event.returnValue`.

> :warning: **WARNING**: Sending a synchronous message will block the whole
> renderer process until the reply is received, so use this method only as a
> last resort. It's much better to use the asynchronous version,
> [`invoke()`](ipc-renderer.md#ipcrendererinvokechannel-args).

### `ipcRenderer.postMessage(channel, message, [transfer])`

* `channel` string
* `message` any
* `transfer` MessagePort[] (optional)

Send a message to the main process, optionally transferring ownership of zero
or more [`MessagePort`][] objects.

The transferred `MessagePort` objects will be available in the main process as
[`MessagePortMain`](message-port-main.md) objects by accessing the `ports`
property of the emitted event.

For example:

```js
// Renderer process
const { port1, port2 } = new MessageChannel()
ipcRenderer.postMessage('port', { message: 'hello' }, [port1])

// Main process
ipcMain.on('port', (e, msg) => {
  const [port] = e.ports
  // ...
})
```

For more information on using `MessagePort` and `MessageChannel`, see the [MDN
documentation](https://developer.mozilla.org/en-US/docs/Web/API/MessageChannel).

### `ipcRenderer.sendTo(webContentsId, channel, ...args)`

* `webContentsId` number
* `channel` string
* `...args` any[]

Sends a message to a window with `webContentsId` via `channel`.

### `ipcRenderer.sendToHost(channel, ...args)`

* `channel` string
* `...args` any[]

Like `ipcRenderer.send` but the event will be sent to the `<webview>` element in
the host page instead of the main process.

## Event object

The documentation for the `event` object passed to the `callback` can be found
in the [`ipc-renderer-event`](structures/ipc-renderer-event.md) structure docs.

[event-emitter]: https://nodejs.org/api/events.html#events_class_eventemitter
[SCA]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
[`window.postMessage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage
[`MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
