From f5d51b3444a0c205b4bf08fb3609758c18f34831 Mon Sep 17 00:00:00 2001
From: Eric Maciel <elm2178@columbia.edu>
Date: Tue, 27 Oct 2020 18:29:23 -0400
Subject: [PATCH] fix: mounted update error

---
 packages/client/src/useCursor.ts  | 10 ++++++++--
 packages/client/src/useMounted.ts | 17 +++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 packages/client/src/useMounted.ts

diff --git a/packages/client/src/useCursor.ts b/packages/client/src/useCursor.ts
index ed89253..0fb4e8b 100644
--- a/packages/client/src/useCursor.ts
+++ b/packages/client/src/useCursor.ts
@@ -5,14 +5,17 @@ import { Text, Range, Path, NodeEntry } from 'slate'
 import { toJS, Cursor, Cursors } from '@hiveteams/collab-bridge'
 
 import { AutomergeEditor } from './automerge-editor'
+import useMounted from 'useMounted'
 
 const useCursor = (
   e: AutomergeEditor
 ): { decorate: (entry: NodeEntry) => Range[]; cursors: Cursor[] } => {
-  const [cursorData, setSursorData] = useState<Cursor[]>([])
+  const [cursorData, setCursorData] = useState<Cursor[]>([])
+  const mountedRef = useMounted()
 
   useEffect(() => {
     e.onCursor = (data: Cursors) => {
+      if (!mountedRef.current) return
       const ranges: Cursor[] = []
 
       const cursors = toJS(data)
@@ -23,7 +26,10 @@ const useCursor = (
         }
       }
 
-      setSursorData(ranges)
+      // only update state if this component is still mounted
+      if (mountedRef.current) {
+        setCursorData(ranges)
+      }
     }
   }, [])
 
diff --git a/packages/client/src/useMounted.ts b/packages/client/src/useMounted.ts
new file mode 100644
index 0000000..6c51b94
--- /dev/null
+++ b/packages/client/src/useMounted.ts
@@ -0,0 +1,17 @@
+import { useRef, useEffect } from 'react'
+
+function useMounted({ onMount = () => {}, onUnmount = () => {} } = {}) {
+  const isMounted = useRef(false)
+  useEffect(() => {
+    isMounted.current = true
+    onMount()
+    return () => {
+      isMounted.current = false
+      onUnmount()
+    }
+  }, [])
+
+  return isMounted
+}
+
+export default useMounted