fix: support primitive state

src/handle-action.test.ts

@@ -73,3 +73,11 @@ test('supports default state', () => {
   expect(newState1).toEqual({ baz: 0 });
   expect(newState1).toBe(state);
 });
+
+test('supports primitive state', () => {
+  const ac1 = createAction<void>('toUpperCase');
+  const state = 'foobarbaz';
+  const re = handleAction<string>(ac1, s => s.toUpperCase(), state);
+  const newState1 = re(state, ac1());
+  expect(newState1).toBe('FOOBARBAZ');
+});

src/handle-action.ts

@@ -3,6 +3,7 @@ import {
   Draft,
   createDraft,
   finishDraft,
+  isDraftable,
 } from 'immer';
 import {
   // eslint-disable-next-line no-unused-vars
@@ -22,15 +23,19 @@ export default function handleAction<S, AC extends TsActionCreator<any> = any>(
 ): Reducer<S, ReturnType<AC>> {
   return (state: S | undefined, action: ReturnType<AC>) => {
     if (action.type === ac.type && state) {
-      const draft = createDraft(state);
-      const reResult = re(draft, action);
-      const finishedDraft = finishDraft(draft);
+      if (isDraftable(state)) {
+        const draft = createDraft(state);
+        const reResult = re(draft, action);
+        const finishedDraft = finishDraft(draft);
 
-      if (finishedDraft === state && reResult !== undefined) {
-        return reResult;
-      }
+        if (finishedDraft === state && reResult !== undefined) {
+          return reResult;
+        }
 
-      return finishedDraft;
+        return finishedDraft;
+      }
+      // Support primitive-returning reducers
+      return re(state as Draft<S>, action);
     }
     return (state || s) as any;
   };