Fix for arrays not being properly updated in writable stores

src/automerge-writable-store.ts

@@ -1,5 +1,6 @@
 import { type Updater, type Writable } from "svelte/store";
 import type { AutomergeSvelteStoreInterface } from "./automerge-svelte-store.type";
+import { diffArrays } from "diff";
 
 export class AutomergeWritableStore<T>
   implements Writable<T>, AutomergeSvelteStoreInterface<T>
@@ -8,7 +9,7 @@ export class AutomergeWritableStore<T>
 
   constructor(rootStore: AutomergeSvelteStoreInterface<T>) {
     this.#rootStore = rootStore;
-    if (typeof rootStore.get() !== "object") {
+    if (typeof rootStore.get() === "string") {
       throw new Error(
         "We cannot currently create writable store from string value",
       );
@@ -37,7 +38,19 @@ export class AutomergeWritableStore<T>
 
   set(value: T) {
     this.#rootStore.change((doc) => {
-      if (
+      if (Array.isArray(doc) && Array.isArray(value)) {
+        const diffs = diffArrays(doc, value);
+        diffs.forEach((diff) => {
+          if (diff.added) {
+            doc.push(...diff.value);
+          } else if (diff.removed) {
+            const index = doc.indexOf(diff.value[0]);
+            if (index > -1) {
+              doc.splice(index, 1);
+            }
+          }
+        });
+      } else if (
         doc !== null &&
         typeof doc === "object" &&
         typeof value === "object"

tests/writable-store.test.ts

@@ -85,6 +85,12 @@ describe("writable store", () => {
       "world",
       "hello there world",
     ]);
+
+    writableStore.update((doc) => {
+      return doc.filter((item) => item !== "world");
+    });
+
+    expect(get(writableStore)).toEqual(["hello", "hello there world"]);
   });
 
   test("writable non object stores throw an error", () => {