# MessagePortMain

`MessagePortMain` is the main-process-side equivalent of the DOM
[`MessagePort`][] object. It behaves similarly to the DOM version, with the
exception that it uses the Node.js `EventEmitter` event system, instead of the
DOM `EventTarget` system. This means you should use `port.on('message', ...)`
to listen for events, instead of `port.onmessage = ...` or
`port.addEventListener('message', ...)`

See the [Channel Messaging API][] documentation for more information on using
channel messaging.

`MessagePortMain` is an [EventEmitter][event-emitter].

## Class: MessagePortMain

> Port interface for channel messaging in the main process.

Process: [Main](../glossary.md#main-process)

### Instance Methods

#### `port.postMessage(message, [transfer])`

* `message` any
* `transfer` MessagePortMain[] (optional)

Sends a message from the port, and optionally, transfers ownership of objects
to other browsing contexts.

#### `port.start()`

Starts the sending of messages queued on the port. Messages will be queued
until this method is called.

#### `port.close()`

Disconnects the port, so it is no longer active.

### Instance Events

#### Event: 'message'

Returns:

* `messageEvent` Object
  * `data` any
  * `ports` MessagePortMain[]

Emitted when a MessagePortMain object receives a message.

#### Event: 'close'

Emitted when the remote end of a MessagePortMain object becomes disconnected.

[`MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
[Channel Messaging API]: https://developer.mozilla.org/en-US/docs/Web/API/Channel_Messaging_API