fix: new users no longer nuke existing shared state

src/index.spec.ts

@@ -426,4 +426,31 @@ describe("Yjs middleware (vanilla)", () =>
       { "name": "bob", "status": "online", }
     ]);
   });
+
+  it("Does not reset state on join.", () =>
+  {
+    type Store =
+    {
+      count: number,
+      increment: () => void,
+    };
+
+    const doc = new Y.Doc();
+    doc.getMap("hello").set("count", 12);
+
+    const api =
+      create<Store>(yjs(
+        doc,
+        "hello",
+        (set) =>
+          ({
+            "count": 0,
+            "increment": () =>
+              set((state) =>
+                ({ "count": state.count + 1, })),
+          })
+      ));
+
+    expect(api.getState().count).toBe(12);
+  });
 });

src/index.ts

@@ -6,7 +6,7 @@ import {
   StoreApi,
 } from "zustand/vanilla";
 import * as Y from "yjs";
-import { patchSharedType, patchStore, } from "./patching";
+import { patchObject, patchSharedType, patchStore, } from "./patching";
 
 /**
  * This function is the middleware the sets up the Zustand store to mirror state
@@ -45,7 +45,7 @@ const yjs = <S extends State>(
      * Capture the initial state so that we can initialize the Yjs store to the
      * same values as the initial values of the Zustand store.
      */
-    const initialState = config(
+    let initialState = config(
       /*
        * Create a new set function that defers to the original and then passes
        * the new state to patchSharedType.
@@ -68,7 +68,11 @@ const yjs = <S extends State>(
     );
 
     // Initialize the Yjs store.
-    patchSharedType(map, initialState);
+    if (Array.from(map.keys()).length === 0)
+      patchSharedType(map, initialState);
+
+    else
+      initialState = patchObject(initialState, map.toJSON());
 
     /*
      * Whenever the Yjs store changes, we perform a set operation on the local