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# Method name: publish(channel: Channel, payload: any, options: PublishOptions)

# Method package: wixRealtimeBackend

# Method menu location: wixRealtimeBackend --> publish

# Method Link: https://dev.wix.com/docs/velo/velo-only-apis/wix-realtime-backend/publish.md

# Method Description:

Publishes a message to a channel or channel resource.

The `publish()` function publishes a message to the specified channel or
 channel resource. 

 When site visitors subscribe to a channel, they do not 
 receive messages published to a resource on that same channel. Similarly, 
 when site visitors subscribe to a channel resource, they do not 
 receive messages published to that same channel without a specified resource.

 To publish a message to specific users only, specify the users by ID in
 the `PublishOptions` object sent to the `options` parameter.

 To include the ID of the user who triggered the publish in the published message,
 set the `includePublisher` property of the `PublishOptions` object to `true`.



# Method Code Examples:

*** Note: do not assume any prop names or enum values other than the ones in the example.

## Publish to a channel

```javascript
import wixRealtimeBackend from 'wix-realtime-backend';

// ...

const channel = {"name": "someChannel"};

wixRealtimeBackend.publish(channel, "My message")
  .then(() => {
    // published
  });
```

## Publish to a resource on a channel

```javascript
import wixRealtimeBackend from 'wix-realtime-backend';

// ...

const channel = {
  "name": "someChannel",
  "resourceId": "someId"
};

wixRealtimeBackend.publish(channel, "My message")
  .then(() => {
    // published
  });
```

## Publish to specific users on a channel and include publisher information

```javascript
import wixRealtimeBackend from 'wix-realtime-backend';

// ...

const channel = {"name": "someChannel"};

const message = {
  "firstKey": "firstValue",
  "secondKey": "secondValue"
};

const user1 = // get ID of first user to publish to
const user2 = // get ID of second user to publish to

const options = {
  "users" : [user1, user2],
  "includePublisher": true
};

wixRealtimeBackend.publish(channel, message, options)
  .then( () => {
    // published
  } );
```

## Send and receive messages across multiple channels and channel resources

```javascript
import { subscribe } from 'wix-realtime-frontend';
import { publishMessage } from 'backend/realtime';

const channelA = { name: 'a' };
const channelB = { name: 'b' };
const channelB1 = { name: 'b', resourceId: '1' };
const channelB2 = { name: 'b', resourceId: '2' };

$w.onReady(function () {
  subscribeToChannels();
  setupPublishButtons();
});

function subscribeToChannels() {
  subscribe(channelA, messageHandler);
  subscribe(channelB, messageHandler);
  subscribe(channelB1, messageHandler);
  subscribe(channelB2, messageHandler);
}

function setupPublishButtons() {
  $w('#publishButtonA').onClick(event => {
    publish(event.target, channelA);
  });

  $w('#publishButtonB').onClick(event => {
    publish(event.target, channelB);
  });

  $w('#publishButtonB1').onClick(event => {
    publish(event.target, channelB1);
  });

  $w('#publishButtonB2').onClick(event => {
    publish(event.target, channelB2);
  });
}

async function publish(button, channel) {
  if ($w('#message').value) {
    button.disable();
    $w('#message').disable();

    await publishMessage(channel, $w('#message').value);

    $w('#message').value = undefined;
    $w('#message').enable();
    button.enable();
  }
}

function messageHandler(message, channel) {
  let textBoxId;

  if (channel.name === 'a') {
    textBoxId = '#receivedMessagesA';
  } else { // Channel B - check resource ID
    if (channel.resourceId === '1') {
      textBoxId = '#receivedMessagesB1';
    } else if (channel.resourceId === '2') {
      textBoxId = '#receivedMessagesB2';
    } else {
      textBoxId = '#receivedMessagesB';
    }
  }

  $w(textBoxId).value += (message.payload + '\n');
}
```

---