fix(undo): adding initial state in historyAtom (#828)

* fix: adding initial state in historyAtom

* refactor: fix without modify AtomProto

* refactor: comma

packages/undo/src/index.test.ts

@@ -55,6 +55,18 @@ test('withUndo', async () => {
   ;('👍') //?
 })
 
+test('withUndo without getting historyAtom before first change', async () => {
+  const a = atom(0).pipe(withUndo({ length: 5 }))
+  const ctx = createTestCtx()
+
+  a(ctx, 1)
+  assert.is(ctx.get(a), 1)
+  assert.is(ctx.get(a.isUndoAtom), true)
+  assert.is(ctx.get(a.isRedoAtom), false)
+  assert.equal(ctx.get(a.historyAtom), [0, 1])
+  ;('👍') //?
+})
+
 test('limit', () => {
   const a = atom(0).pipe(withUndo({ length: 5 }))
   const ctx = createTestCtx()

packages/undo/src/index.ts

@@ -63,10 +63,18 @@ export const withUndo =
     if (!anAtom.undo) {
       const { name } = anAtom.__reatom
 
-      const historyAtom = (anAtom.historyAtom = atom<Array<AtomState<T>>>(
+      const historyAtom = anAtom.historyAtom = atom<Array<AtomState<T>>>(
         [],
         `${name}.Undo._historyAtom`,
-      ).pipe(withInit((ctx) => [ctx.get(anAtom)])))
+      )
+
+      anAtom.pipe(
+        withInit((ctx, init) => {
+          const state = init(ctx)
+          historyAtom(ctx, [state])
+          return state
+        }),
+      )
 
       const positionAtom = (anAtom.positionAtom = atom(0, `${name}._position`))