[#153] feat: 실시간 동기화 시 기존 caret이 적용되도록 수정

Author: domino8788

frontend/src/hooks/useSocket.tsx

@@ -1,5 +1,5 @@
 import { useSetRecoilState } from 'recoil';
-import { blockMapState, pagesState, focusState } from '@/stores';
+import { blockMapState, pagesState } from '@/stores';
 import { pageIO, pageListIO } from '@/socket';
 import { BlockMap, Page } from '@/schemes';
 import { useEffect } from 'react';
@@ -33,6 +33,18 @@ const useSocket = () => {
     });
 
     pageIO.on('PageUpdate', (updatedBlockMap: BlockMap) => {
+      const { focusOffset: beforeOffset, focusNode } = window.getSelection();
+      const length = (focusNode as any)?.length;
+      if (length) {
+        focusNode.parentElement.blur();
+        setTimeout(() => {
+          const sel = window.getSelection();
+          sel.collapse(
+            sel.focusNode,
+            beforeOffset < length ? beforeOffset : length,
+          );
+        });
+      }
       setBlockMap(updatedBlockMap);
     });