129 lines
4.1 KiB
Markdown
129 lines
4.1 KiB
Markdown
---
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title: "ipcMain"
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description: "Communicate asynchronously from the main process to renderer processes."
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slug: ipc-main
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hide_title: false
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---
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# ipcMain
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> Communicate asynchronously from the main process to renderer processes.
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Process: [Main](../glossary.md#main-process)
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The `ipcMain` module is an [Event Emitter][event-emitter]. When used in the main
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process, it handles asynchronous and synchronous messages sent from a renderer
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process (web page). Messages sent from a renderer will be emitted to this
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module.
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For usage examples, check out the [IPC tutorial][].
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## Sending messages
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It is also possible to send messages from the main process to the renderer
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process, see [webContents.send][web-contents-send] for more information.
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* When sending a message, the event name is the `channel`.
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* To reply to a synchronous message, you need to set `event.returnValue`.
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* To send an asynchronous message back to the sender, you can use
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`event.reply(...)`. This helper method will automatically handle messages
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coming from frames that aren't the main frame (e.g. iframes) whereas
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`event.sender.send(...)` will always send to the main frame.
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## Methods
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The `ipcMain` module has the following method to listen for events:
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### `ipcMain.on(channel, listener)`
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* `channel` string
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* `listener` Function
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* `event` [IpcMainEvent][ipc-main-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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### `ipcMain.once(channel, listener)`
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* `channel` string
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* `listener` Function
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* `event` [IpcMainEvent][ipc-main-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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### `ipcMain.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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### `ipcMain.removeAllListeners([channel])`
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* `channel` string (optional)
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Removes listeners of the specified `channel`.
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### `ipcMain.handle(channel, listener)`
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* `channel` string
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* `listener` Function\<Promise\<any\> | any\>
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* `event` [IpcMainInvokeEvent][ipc-main-invoke-event]
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* `...args` any[]
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Adds a handler for an `invoke`able IPC. This handler will be called whenever a
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renderer calls `ipcRenderer.invoke(channel, ...args)`.
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If `listener` returns a Promise, the eventual result of the promise will be
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returned as a reply to the remote caller. Otherwise, the return value of the
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listener will be used as the value of the reply.
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```js title='Main Process' @ts-type={somePromise:(...args:unknown[])=>Promise<unknown>}
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ipcMain.handle('my-invokable-ipc', async (event, ...args) => {
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const result = await somePromise(...args)
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return result
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})
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```
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```js title='Renderer Process' @ts-type={arg1:unknown} @ts-type={arg2:unknown}
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async () => {
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const result = await ipcRenderer.invoke('my-invokable-ipc', arg1, arg2)
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// ...
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}
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```
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The `event` that is passed as the first argument to the handler is the same as
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that passed to a regular event listener. It includes information about which
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WebContents is the source of the invoke request.
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Errors thrown through `handle` in the main process are not transparent as they
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are serialized and only the `message` property from the original error is
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provided to the renderer process. Please refer to
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[#24427](https://github.com/electron/electron/issues/24427) for details.
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### `ipcMain.handleOnce(channel, listener)`
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* `channel` string
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* `listener` Function\<Promise\<any\> | any\>
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* `event` [IpcMainInvokeEvent][ipc-main-invoke-event]
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* `...args` any[]
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Handles a single `invoke`able IPC message, then removes the listener. See
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`ipcMain.handle(channel, listener)`.
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### `ipcMain.removeHandler(channel)`
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* `channel` string
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Removes any handler for `channel`, if present.
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[IPC tutorial]: ../tutorial/ipc.md
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[event-emitter]: https://nodejs.org/api/events.html#events_class_eventemitter
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[web-contents-send]: ../api/web-contents.md#contentssendchannel-args
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[ipc-main-event]:../api/structures/ipc-main-event.md
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[ipc-main-invoke-event]:../api/structures/ipc-main-invoke-event.md
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