Merge pull request #566 from share/docs-null-presence

📝 Update presence documentation

docs/api/presence.md

@@ -143,6 +143,9 @@ presence.on('receive', function(id, value) { ... });
 
 > The presence value. The structure of this object will depend on the [type]({{ site.baseurl }}{% link types/index.md %})
 
+{: .info }
+> A `null` value means the remote client is no longer present in the document (e.g. they disconnected)
+
 ### `'error'`
 
 An error has occurred.

docs/presence.md

@@ -22,6 +22,14 @@ In this case, clients just need to subscribe to a common channel using [`connect
 ```js
 const presence = connection.getPresence('my-channel')
 presence.subscribe()
+
+presence.on('receive', (presenceId, update) => {
+  if (update === null) {
+    // The remote client is no longer present in the document
+  } else {
+    // Handle the new value by updating UI, etc.
+  }
+})
 ```
 
 In order to send presence information to other clients, a [`LocalPresence`]({{ site.baseurl }}{% link api/local-presence.md %}) should be created. The presence object can take any arbitrary value
@@ -51,6 +59,14 @@ Clients subscribe to a particular [`Doc`]({{ site.baseurl }}{% link api/doc.md %
 ```js
 const presence = connection.getDocPresence(collection, id)
 presence.subscribe()
+
+presence.on('receive', (presenceId, update) => {
+  if (update === null) {
+    // The remote client is no longer present in the document
+  } else {
+    // Handle the new value by updating UI, etc.
+  }
+})
 ```
 
 The shape of the presence value will be defined by the [type]({{ site.baseurl }}{% link types/index.md %}):