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# Method name: realtime_check_permission(channel: Channel, subscriber: Subscriber)

# Method package: wixRealtimeBackend

# Method menu location: wixRealtimeBackend --> realtime_check_permission

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

# Method Description:

Checks permissions for a subscriber on a channel or channel resource.

The `realtime_check_permission` hook is triggered when a site visitor subscribes
 to a channel to check what permissions the subscriber will have.

 The `realtime_check_permission()` function is not a function that you call from
 your code. You define the function in a file named **realtime-permissions.js**
 in your site's Backend section.



__Important:__
- If this function isn't defined, all subscribers will receive the default permissions: `{"read": true}`.
- In Wix Studio, you don't need to define this function, but you must create a backend file named **realtime-permissions.js**. Without this file, subscriptions will fail.




 Implement permissions logic for channels and subscribers by either:

 + Including all permissions logic in the body of this function.
 + Use the `PermissionsRouter` to add permissions
   logic per channel. Then call [`check()`](https://dev.wix.com/docs/velo/velo-only-apis/wix-realtime-backend/permissions-router/check.md) in the body of
   this function and return the permissions object it returns.


> **Note:** When previewing your site, permissions for read are always granted.



# Method Code Examples:

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

## Grant permissions for a channel based on subscriber type

```javascript
// In realtime-permissions.js

export function realtime_check_permission(channel, subscriber) {
  // set default permissions
  let permissions =  {"read": true};
  
  if(channel.name === "MembersOnly") {
    if(subscriber.type === "Member"){
      permissions.read = true; 
    }
    else {
      permissions.read = false;
    }
  }
  
  return permissions;
}
```

## Grant permissions for a channel based on subscriber type using the permissions router

```javascript
// In realtime-permissions.js

import {permissionsRouter} from 'wix-realtime-backend';

permissionsRouter.default( (channel, subscriber) => {
  return {"read": true};
} );

const membersOnlyChannel = {"name": "MembersOnly"};

permissionsRouter.add(membersOnlyChannel, (channel, subscriber) => {
  if(subscriber.type === "Member") {
    return {"read": true};
  }
  else {
    return {"read": false};
  }
});

export function realtime_check_permission(channel, subscriber) {
  return permissionsRouter.check(channel,subscriber);
}
```

## Grant permissions based on user data

```javascript
// In realtime-permissions.js

import { members } from `wix-members-backend`;

export async function realtime_check_permission(channel, subscriber) {
  // set default permissions
  let permissions =  { "read": true };

  if(channel.name === "BobsOnly") {
    let member = await members.getMember(subscriber.id, { fieldsets: ['FULL'] });
    if(member.contactDetails.firstName === "Bob") {
      permissions.read = true;
    }
    else {
      permissions.read = false;
    }
  }
  
  return permissions;
}
```

## Grant permissions based on user data using the permissions router

```javascript
// In realtime-permissions.js

import { members } from `wix-members-backend`;
import { permissionsRouter } from 'wix-realtime-backend';

permissionsRouter.default((channel, subscriber) => {
  return {"read": true};
});

const membersOnlyChannel = {"name": "MembersOnly"};

permissionsRouter.add( membersOnlyChannel, async (channel, subscriber) => {
  let member = await members.getMember(subscriber.id, { fieldsets: ['FULL'] });
  
  if(channel.resourceId === "BobsOnly") {
    if(member.contactDetails.firstName === "Bob") {
      return { "read": true };
    }
    else {
      return { "read": false };
    }
  }
  else {
    return { "read": true };
  }
} );

export function realtime_check_permission(channel, subscriber) {
  return permissionsRouter.check(channel, subscriber);
}
```

## Check permissions across multiple channels and channel resources

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

const updatesChannel = {name: 'updates'};
const updatesMembersChannel = {name: 'updates', resourceId: 'members'};
const updatesAdminsChannel = {name: 'updates', resourceId: 'admins'};
const updatesGuestsChannel = {name: 'updates', resourceId: 'guests'};

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

function subscribeToChannels() {
  subscribe(updatesChannel, messageHandler)
    .catch(() => console.log('Not subscribed to updates channel'));
  subscribe(updatesMembersChannel, messageHandler)
    .catch(() => console.log('Not subscribed to members channel'));
  subscribe(updatesAdminsChannel, messageHandler)
    .catch(() => console.log('Not subscribed to admins channel'));
  subscribe(updatesGuestsChannel, messageHandler)
    .catch(() => console.log('Not subscribed to guest channel'));
}

function messageHandler(message, channel) {
  const channelName = channel.name;
  const channelResource = channel.resourceId ? `-${channel.resourceId}` : '';
  let newMessageLine = `${channelName}${channelResource}: ${message.payload}\n`;
  $w('#receivedMessages').value += newMessageLine;
}

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

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

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

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

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();
  }
}
```

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