215 lines
7.6 KiB
Markdown
215 lines
7.6 KiB
Markdown
---
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title: "ipcRenderer"
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description: "Communicate asynchronously from a renderer process to the main process."
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slug: ipc-renderer
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hide_title: false
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---
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# ipcRenderer
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> Communicate asynchronously from a renderer process to the main process.
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Process: [Renderer](../glossary.md#renderer-process)
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The `ipcRenderer` module is an [EventEmitter][event-emitter]. It provides a few
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methods so you can send synchronous and asynchronous messages from the render
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process (web page) to the main process. You can also receive replies from the
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main process.
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See [IPC tutorial](../tutorial/ipc.md) for code examples.
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## Methods
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The `ipcRenderer` module has the following method to listen for events and send messages:
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### `ipcRenderer.on(channel, listener)`
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* `channel` string
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* `listener` Function
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* `event` [IpcRendererEvent][ipc-renderer-event]
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* `...args` any[]
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Listens to `channel`, when a new message arrives `listener` would be called with
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`listener(event, args...)`.
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### `ipcRenderer.once(channel, listener)`
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* `channel` string
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* `listener` Function
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* `event` [IpcRendererEvent][ipc-renderer-event]
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* `...args` any[]
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Adds a one time `listener` function for the event. This `listener` is invoked
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only the next time a message is sent to `channel`, after which it is removed.
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### `ipcRenderer.removeListener(channel, listener)`
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* `channel` string
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* `listener` Function
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* `...args` any[]
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Removes the specified `listener` from the listener array for the specified
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`channel`.
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### `ipcRenderer.removeAllListeners(channel)`
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* `channel` string
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Removes all listeners, or those of the specified `channel`.
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### `ipcRenderer.send(channel, ...args)`
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* `channel` string
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* `...args` any[]
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Send an asynchronous message to the main process via `channel`, along with
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arguments. Arguments will be serialized with the [Structured Clone
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Algorithm][SCA], just like [`window.postMessage`][], so prototype chains will not be
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included. Sending Functions, Promises, Symbols, WeakMaps, or WeakSets will
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throw an exception.
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> **NOTE:** Sending non-standard JavaScript types such as DOM objects or
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> special Electron objects will throw an exception.
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>
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> Since the main process does not have support for DOM objects such as
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> `ImageBitmap`, `File`, `DOMMatrix` and so on, such objects cannot be sent over
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> Electron's IPC to the main process, as the main process would have no way to decode
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> them. Attempting to send such objects over IPC will result in an error.
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The main process handles it by listening for `channel` with the
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[`ipcMain`](./ipc-main.md) module.
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If you need to transfer a [`MessagePort`][] to the main process, use [`ipcRenderer.postMessage`](#ipcrendererpostmessagechannel-message-transfer).
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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).
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### `ipcRenderer.invoke(channel, ...args)`
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* `channel` string
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* `...args` any[]
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Returns `Promise<any>` - Resolves with the response from the main process.
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Send a message to the main process via `channel` and expect a result
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asynchronously. Arguments will be serialized with the [Structured Clone
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Algorithm][SCA], just like [`window.postMessage`][], so prototype chains will not be
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included. Sending Functions, Promises, Symbols, WeakMaps, or WeakSets will
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throw an exception.
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The main process should listen for `channel` with
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[`ipcMain.handle()`](./ipc-main.md#ipcmainhandlechannel-listener).
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For example:
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```javascript @ts-type={someArgument:unknown} @ts-type={doSomeWork:(arg:unknown)=>Promise<unknown>}
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// Renderer process
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ipcRenderer.invoke('some-name', someArgument).then((result) => {
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// ...
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})
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// Main process
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ipcMain.handle('some-name', async (event, someArgument) => {
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const result = await doSomeWork(someArgument)
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return result
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})
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```
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If you need to transfer a [`MessagePort`][] to the main process, use [`ipcRenderer.postMessage`](#ipcrendererpostmessagechannel-message-transfer).
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If you do not need a response to the message, consider using [`ipcRenderer.send`](#ipcrenderersendchannel-args).
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> **Note**
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> Sending non-standard JavaScript types such as DOM objects or
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> special Electron objects will throw an exception.
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>
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> Since the main process does not have support for DOM objects such as
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> `ImageBitmap`, `File`, `DOMMatrix` and so on, such objects cannot be sent over
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> Electron's IPC to the main process, as the main process would have no way to decode
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> them. Attempting to send such objects over IPC will result in an error.
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> **Note**
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> If the handler in the main process throws an error,
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> the promise returned by `invoke` will reject.
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> However, the `Error` object in the renderer process
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> will not be the same as the one thrown in the main process.
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### `ipcRenderer.sendSync(channel, ...args)`
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* `channel` string
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* `...args` any[]
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Returns `any` - The value sent back by the [`ipcMain`](./ipc-main.md) handler.
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Send a message to the main process via `channel` and expect a result
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synchronously. Arguments will be serialized with the [Structured Clone
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Algorithm][SCA], just like [`window.postMessage`][], so prototype chains will not be
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included. Sending Functions, Promises, Symbols, WeakMaps, or WeakSets will
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throw an exception.
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> **NOTE:** Sending non-standard JavaScript types such as DOM objects or
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> special Electron objects will throw an exception.
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>
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> Since the main process does not have support for DOM objects such as
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> `ImageBitmap`, `File`, `DOMMatrix` and so on, such objects cannot be sent over
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> Electron's IPC to the main process, as the main process would have no way to decode
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> them. Attempting to send such objects over IPC will result in an error.
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The main process handles it by listening for `channel` with [`ipcMain`](./ipc-main.md) module,
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and replies by setting `event.returnValue`.
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> :warning: **WARNING**: Sending a synchronous message will block the whole
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> renderer process until the reply is received, so use this method only as a
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> last resort. It's much better to use the asynchronous version,
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> [`invoke()`](./ipc-renderer.md#ipcrendererinvokechannel-args).
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### `ipcRenderer.postMessage(channel, message, [transfer])`
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* `channel` string
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* `message` any
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* `transfer` MessagePort[] (optional)
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Send a message to the main process, optionally transferring ownership of zero
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or more [`MessagePort`][] objects.
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The transferred `MessagePort` objects will be available in the main process as
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[`MessagePortMain`](./message-port-main.md) objects by accessing the `ports`
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property of the emitted event.
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For example:
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```js
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// Renderer process
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const { port1, port2 } = new MessageChannel()
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ipcRenderer.postMessage('port', { message: 'hello' }, [port1])
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// Main process
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ipcMain.on('port', (e, msg) => {
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const [port] = e.ports
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// ...
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})
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```
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For more information on using `MessagePort` and `MessageChannel`, see the [MDN
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documentation](https://developer.mozilla.org/en-US/docs/Web/API/MessageChannel).
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### `ipcRenderer.sendTo(webContentsId, channel, ...args)` _Deprecated_
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* `webContentsId` number
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* `channel` string
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* `...args` any[]
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Sends a message to a window with `webContentsId` via `channel`.
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### `ipcRenderer.sendToHost(channel, ...args)`
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* `channel` string
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* `...args` any[]
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Like `ipcRenderer.send` but the event will be sent to the `<webview>` element in
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the host page instead of the main process.
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[event-emitter]: https://nodejs.org/api/events.html#events_class_eventemitter
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[SCA]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
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[`window.postMessage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage
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[`MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
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[ipc-renderer-event]: ./structures/ipc-renderer-event.md
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