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Add createReducer default handler #273

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1bd847d
Add createReducer default handler
rafael81 May 12, 2026
a6e6f25
Handle Redux internal default actions
rafael81 May 12, 2026
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23 changes: 23 additions & 0 deletions README.md
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -760,6 +760,7 @@ createReducer<TState, TRootAction>(initialState)
.handleAction([actionCreator1, actionCreator2, ...actionCreatorN], reducer)
.handleType(type, reducer)
.handleType([type1, type2, ...typeN], reducer)
.defaultHandler(reducer)
```

Examples:
Expand Down Expand Up @@ -805,6 +806,28 @@ const counterReducer = createReducer<State, Action>(0)
.handleType('INCREMENT', (state, _) => state + 1);
```

**Default handler:**
```ts
type State = boolean;
type Action =
| { type: 'REQUEST_START' }
| { type: 'REQUEST_SUCCESS' }
| { type: 'REQUEST_FAILURE' };

const loadingReducer = createReducer<State, Action>(false)
.handleType('REQUEST_START', () => true)
.defaultHandler(() => false);
```

The default handler runs for actions that do not have an explicit handler. It
does not run for Redux initialization actions unless you pass `true` as the
second argument:
```ts
const reducer = createReducer<State, Action>(false)
.handleType('REQUEST_START', () => true)
.defaultHandler(() => false, true);
```

**Extend or compose reducers - every operation is completely typesafe:**
```ts
const newCounterReducer = createReducer<State, Action>(0)
Expand Down
16 changes: 15 additions & 1 deletion src/__snapshots__/create-reducer.spec.ts.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,11 @@ exports[`Type refinement checks action (type) should match snapshot 3`] = `"T.Em

exports[`Type refinement checks action (type) should match snapshot 4`] = `"T.EmptyAction<\\"foo4\\">"`;

exports[`Type refinement checks reducer.handlers (type) should match snapshot 1`] = `"Record<\\"foo1\\" | \\"foo2\\" | \\"foo3\\" | \\"foo4\\", (state: { foo: string | null; }, action: T.PayloadAction<\\"foo1\\", string> | T.PayloadAction<\\"foo2\\", string> | T.EmptyAction<\\"foo3\\"> | T.EmptyAction<\\"foo4\\">) => { foo: string | null; }>"`;
exports[`Type refinement checks action (type) should match snapshot 5`] = `"T.EmptyAction<\\"foo5\\">"`;

exports[`Type refinement checks reducer.handlers (type) should match snapshot 1`] = `"Record<\\"foo1\\" | \\"foo2\\" | \\"foo3\\" | \\"foo4\\", (state: { foo: string | null; }, action: T.PayloadAction<\\"foo1\\", string> | T.PayloadAction<\\"foo2\\", string> | T.EmptyAction<\\"foo3\\"> | T.EmptyAction<\\"foo4\\"> | T.EmptyAction<\\"foo5\\">) => { foo: string | null; }>"`;

exports[`Type refinement checks reducerDefaultResult (type) should match snapshot 1`] = `"{ foo: string | null; }"`;

exports[`Type refinement checks reducerResult (type) should match snapshot 1`] = `"{ foo: string | null; }"`;

Expand All @@ -26,6 +30,10 @@ exports[`Type refinement checks state (type) should match snapshot 3`] = `"{ foo

exports[`Type refinement checks state (type) should match snapshot 4`] = `"{ foo: string | null; }"`;

exports[`Type refinement checks state (type) should match snapshot 5`] = `"{ foo: string | null; }"`;

exports[`With Action Creators action (type) should match snapshot 1`] = `"T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">"`;

exports[`With Action Creators counterReducer1.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\" | \\"INCREMENT\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Creators counterReducer2.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\" | \\"INCREMENT\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;
Expand All @@ -34,10 +42,16 @@ exports[`With Action Creators counterReducer3.handlers (type) should match snaps

exports[`With Action Creators counterReducer4.handlers (type) should match snapshot 1`] = `"Record<\\"INCREMENT\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Creators counterReducer5.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Types action (type) should match snapshot 1`] = `"T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">"`;

exports[`With Action Types counterReducer1.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\" | \\"INCREMENT\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Types counterReducer2.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\" | \\"INCREMENT\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Types counterReducer3.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Types counterReducer4.handlers (type) should match snapshot 1`] = `"Record<\\"INCREMENT\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;

exports[`With Action Types counterReducer5.handlers (type) should match snapshot 1`] = `"Record<\\"ADD\\", (state: number, action: T.PayloadAction<\\"ADD\\", number> | T.EmptyAction<\\"INCREMENT\\"> | T.EmptyAction<\\"DECREMENT\\">) => number>"`;
81 changes: 80 additions & 1 deletion src/create-reducer.spec.snap.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,22 @@ const initialState = 0;
// @dts-jest:pass
Object.keys({ ...emptyReducer.handlers }); // => []

const counterReducer5 = emptyReducer
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler((state, action) => {
// @dts-jest:pass:snap -> T.EmptyAction<"INCREMENT"> | T.EmptyAction<"DECREMENT">
action;

return state - 1;
});

// @dts-jest:pass:snap -> Record<"ADD", (state: number, action: T.PayloadAction<"ADD", number> | T.EmptyAction<"INCREMENT"> | T.EmptyAction<"DECREMENT">) => number>
counterReducer5.handlers;
// @dts-jest:pass
Object.keys({ ...counterReducer5.handlers }); // => [ "ADD"]
// @dts-jest:pass
Object.keys({ ...emptyReducer.handlers }); // => []

{
[
counterReducer1,
Expand All @@ -93,6 +109,8 @@ const initialState = 0;
// @dts-jest:pass
fn(0, add(4)); // => 4
});
counterReducer5(0, decrement());
counterReducer5(0, add(4));
}
}

Expand All @@ -111,6 +129,7 @@ const initialState = 0;
foo2: createAction('foo2')<string>(),
foo3: createAction('foo3')(),
foo4: createAction('foo4')(),
foo5: createAction('foo5')(),
};

type Action = ActionType<typeof actions2>;
Expand Down Expand Up @@ -159,9 +178,20 @@ const initialState = 0;
...state,
foo: 'empty',
};
})
.defaultHandler((state, action) => {
// @dts-jest:pass:snap -> { foo: string | null; }
state;
// @dts-jest:pass:snap -> T.EmptyAction<"foo5">
action;

return {
...state,
foo: 'default',
};
});

// @dts-jest:pass:snap -> Record<"foo1" | "foo2" | "foo3" | "foo4", (state: { foo: string | null; }, action: T.PayloadAction<"foo1", string> | T.PayloadAction<"foo2", string> | T.EmptyAction<"foo3"> | T.EmptyAction<"foo4">) => { foo: string | null; }>
// @dts-jest:pass:snap -> Record<"foo1" | "foo2" | "foo3" | "foo4", (state: { foo: string | null; }, action: T.PayloadAction<"foo1", string> | T.PayloadAction<"foo2", string> | T.EmptyAction<"foo3"> | T.EmptyAction<"foo4"> | T.EmptyAction<"foo5">) => { foo: string | null; }>
reducer.handlers;

{
Expand All @@ -180,6 +210,10 @@ const initialState = 0;
// @dts-jest:pass:snap -> { foo: string | null; }
reducerResult; // => { foo: "empty" }
});

const reducerDefaultResult = reducer(defaultState, actions2.foo5());
// @dts-jest:pass:snap -> { foo: string | null; }
reducerDefaultResult; // => { foo: "default" }
}
}

Expand Down Expand Up @@ -230,6 +264,21 @@ const initialState = 0;
// @dts-jest:pass
Object.keys({ ...reducerTest.handlers }); // => []

const counterReducer5 = reducerTest
.handleType('ADD', (state, action) => state + action.payload)
.defaultHandler((state, action) => {
// @dts-jest:pass:snap -> T.EmptyAction<"INCREMENT"> | T.EmptyAction<"DECREMENT">
action;

return state - 1;
});
// @dts-jest:pass:snap -> Record<"ADD", (state: number, action: T.PayloadAction<"ADD", number> | T.EmptyAction<"INCREMENT"> | T.EmptyAction<"DECREMENT">) => number>
counterReducer5.handlers;
// @dts-jest:pass
Object.keys({ ...counterReducer5.handlers }); // => [ "ADD"]
// @dts-jest:pass
Object.keys({ ...reducerTest.handlers }); // => []

{
[
counterReducer1,
Expand All @@ -254,5 +303,35 @@ const initialState = 0;
// @dts-jest:pass
fn(0, add(4)); // => 4
});
counterReducer5(0, increment());
counterReducer5(0, add(4));
}
}

describe('defaultHandler', () => {
it('handles actions without an explicit handler', () => {
const reducer = createReducer<number, ActionType<typeof actions>>(0)
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler(state => state - 1);

expect(reducer(0, add(4))).toBe(4);
expect(reducer(0, increment())).toBe(-1);
expect(reducer(0, decrement())).toBe(-1);
});

it('does not run for Redux initialization actions by default', () => {
const reducer = createReducer<number, ActionType<typeof actions>>(0)
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler(() => 100);

expect(reducer(undefined, { type: '@@redux/INIT.test' } as any)).toBe(0);
});

it('can opt into running for Redux initialization actions', () => {
const reducer = createReducer<number, ActionType<typeof actions>>(0)
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler(() => 100, true);

expect(reducer(undefined, { type: '@@redux/INIT.test' } as any)).toBe(100);
});
});
79 changes: 79 additions & 0 deletions src/create-reducer.spec.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,22 @@ const initialState = 0;
// @dts-jest:pass
Object.keys({ ...emptyReducer.handlers }); // => []

const counterReducer5 = emptyReducer
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler((state, action) => {
// @dts-jest:pass:snap
action;

return state - 1;
});

// @dts-jest:pass:snap
counterReducer5.handlers;
// @dts-jest:pass
Object.keys({ ...counterReducer5.handlers }); // => [ "ADD"]
// @dts-jest:pass
Object.keys({ ...emptyReducer.handlers }); // => []

{
[
counterReducer1,
Expand All @@ -93,6 +109,8 @@ const initialState = 0;
// @dts-jest:pass
fn(0, add(4)); // => 4
});
counterReducer5(0, decrement());
counterReducer5(0, add(4));
}
}

Expand All @@ -111,6 +129,7 @@ const initialState = 0;
foo2: createAction('foo2')<string>(),
foo3: createAction('foo3')(),
foo4: createAction('foo4')(),
foo5: createAction('foo5')(),
};

type Action = ActionType<typeof actions2>;
Expand Down Expand Up @@ -159,6 +178,17 @@ const initialState = 0;
...state,
foo: 'empty',
};
})
.defaultHandler((state, action) => {
// @dts-jest:pass:snap
state;
// @dts-jest:pass:snap
action;

return {
...state,
foo: 'default',
};
});

// @dts-jest:pass:snap
Expand All @@ -180,6 +210,10 @@ const initialState = 0;
// @dts-jest:pass:snap
reducerResult; // => { foo: "empty" }
});

const reducerDefaultResult = reducer(defaultState, actions2.foo5());
// @dts-jest:pass:snap
reducerDefaultResult; // => { foo: "default" }
}
}

Expand Down Expand Up @@ -230,6 +264,21 @@ const initialState = 0;
// @dts-jest:pass
Object.keys({ ...reducerTest.handlers }); // => []

const counterReducer5 = reducerTest
.handleType('ADD', (state, action) => state + action.payload)
.defaultHandler((state, action) => {
// @dts-jest:pass:snap
action;

return state - 1;
});
// @dts-jest:pass:snap
counterReducer5.handlers;
// @dts-jest:pass
Object.keys({ ...counterReducer5.handlers }); // => [ "ADD"]
// @dts-jest:pass
Object.keys({ ...reducerTest.handlers }); // => []

{
[
counterReducer1,
Expand All @@ -254,5 +303,35 @@ const initialState = 0;
// @dts-jest:pass
fn(0, add(4)); // => 4
});
counterReducer5(0, increment());
counterReducer5(0, add(4));
}
}

describe('defaultHandler', () => {
it('handles actions without an explicit handler', () => {
const reducer = createReducer<number, ActionType<typeof actions>>(0)
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler(state => state - 1);

expect(reducer(0, add(4))).toBe(4);
expect(reducer(0, increment())).toBe(-1);
expect(reducer(0, decrement())).toBe(-1);
});

it('does not run for Redux initialization actions by default', () => {
const reducer = createReducer<number, ActionType<typeof actions>>(0)
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler(() => 100);

expect(reducer(undefined, { type: '@@redux/INIT.test' } as any)).toBe(0);
});

it('can opt into running for Redux initialization actions', () => {
const reducer = createReducer<number, ActionType<typeof actions>>(0)
.handleAction(add, (state, action) => state + action.payload)
.defaultHandler(() => 100, true);

expect(reducer(undefined, { type: '@@redux/INIT.test' } as any)).toBe(100);
});
});
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