all tests pass

package.json

@@ -2,6 +2,7 @@
     "type": "module",
     "dependencies": {
         "@yanick/updeep-remeda": "^2.2.0",
+        "ajv": "^8.12.0",
         "expect-type": "^0.16.0",
         "immer": "^9.0.15",
         "json-schema-shorthand": "^2.0.0",

src/Updux.ts

@@ -22,6 +22,7 @@ import {
     EffectMiddleware,
 } from './effects.js';
 import buildSchema from './schema.js';
+import Ajv from 'ajv';
 
 export type Mutation<A = AnyAction, S = any> = (
     payload: A extends {
@@ -32,6 +33,19 @@ export type Mutation<A = AnyAction, S = any> = (
     action: A,
 ) => (state: S) => S | void;
 
+
+function buildValidateMiddleware(schema) {
+    // @ts-ignore
+    const ajv = new Ajv();
+    const validate = ajv.compile(schema);
+    return (api) => next => action => {
+        next(action);
+        const valid = validate(api.getState());
+
+        if (!valid) throw new Error("validation failed after action " + JSON.stringify(action) + "\n" + JSON.stringify(validate.errors));
+    }
+}
+
 export default class Updux<D extends DuxConfig> {
     #mutations = [];
 
@@ -174,6 +188,7 @@ export default class Updux<D extends DuxConfig> {
     createStore(
         options: Partial<{
             preloadedState: DuxState<D>;
+            validate: boolean;
         }> = {},
     ): EnhancedStore<DuxState<D>> & AugmentedMiddlewareAPI<D> {
         const preloadedState = options.preloadedState;
@@ -184,10 +199,18 @@ export default class Updux<D extends DuxConfig> {
             this.selectors,
         );
 
+        const middleware = [effects];
+
+        if (options.validate) {
+            middleware.unshift(
+                buildValidateMiddleware(this.schema)
+            )
+        }
+
         const store = configureStore({
             reducer: this.reducer,
             preloadedState,
-            middleware: [effects],
+            middleware,
         });
 
         const dispatch: any = store.dispatch;

src/schema.test.ts

@@ -29,3 +29,17 @@ test('schema default inherits from initial state', () => {
 
     expect(dux.schema.default).toEqual(8);
 });
+
+test('validate', () => {
+    const dux = new Updux({
+        initialState: 12,
+        actions: {
+            doItWrong: null,
+        },
+    });
+
+    dux.addMutation('doItWrong', () => () => 'potato' as any);
+
+    const store = dux.createStore({ validate: true });
+    expect(() => store.dispatch.doItWrong()).toThrow();
+});