3b74837020
* Event = Base event type (with preventDefault) * IpcMainEvent = Event that ipcMain emits (with sender, reply, etc.) * IpcRendererEvent = Event that ipcRenderer emits (with sender, senderId, etc.) * KeyboardEvent = Event that we emit with keyboard flags (ctrlKey, altKey, etc.) This will dramatically improve peoples TS experience with IPC events
94 lines
2.8 KiB
Markdown
94 lines
2.8 KiB
Markdown
# 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 instance of the
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[EventEmitter](https://nodejs.org/api/events.html#events_class_eventemitter) class. 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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## 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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An example of sending and handling messages between the render and main
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processes:
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```javascript
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// In main process.
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const { ipcMain } = require('electron')
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ipcMain.on('asynchronous-message', (event, arg) => {
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console.log(arg) // prints "ping"
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event.reply('asynchronous-reply', 'pong')
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})
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ipcMain.on('synchronous-message', (event, arg) => {
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console.log(arg) // prints "ping"
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event.returnValue = 'pong'
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})
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```
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```javascript
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// In renderer process (web page).
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const { ipcRenderer } = require('electron')
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console.log(ipcRenderer.sendSync('synchronous-message', 'ping')) // prints "pong"
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ipcRenderer.on('asynchronous-reply', (event, arg) => {
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console.log(arg) // prints "pong"
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})
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ipcRenderer.send('asynchronous-message', 'ping')
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```
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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
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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
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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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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
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Removes listeners of the specified `channel`.
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## Event object
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The documentation for the `event` object passed to the `callback` can be found
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in the [`ipc-main-event`](structures/ipc-main-event.md) structure docs.
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