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TypeScript: combineReducers returns reducer that accepts partial state #2809

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TypeScript: combineReducers returns reducer that accepts partial state #2809

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2 changes: 1 addition & 1 deletion index.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -86,7 +86,7 @@ export type ReducersMapObject<S = any, A extends Action = Action> = {
* object, and builds a state object with the same shape.
*/
export function combineReducers<S>(reducers: ReducersMapObject<S, any>): Reducer<S>;
export function combineReducers<S, A extends Action = AnyAction>(reducers: ReducersMapObject<S, A>): Reducer<S, A>;
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It seems a shame to break apart from the Reducer type here, but without adding an extra generic to Reducer, I don't see a way around it?

export function combineReducers<S, A extends Action = AnyAction>(reducers: ReducersMapObject<S, A>): (state: Partial<S> | undefined, action: A) => S;


/* store */
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7 changes: 5 additions & 2 deletions test/typescript/reducers.ts
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Expand Up @@ -39,11 +39,14 @@ function simple() {
// typings:expect-error
reducer('string', { type: 'INCREMENT' })

type RootState = { sub: State; sub2: State };

// Combined reducer also accepts any action.
const combined = combineReducers({ sub: reducer })
const combined = combineReducers({ sub: reducer, sub2: reducer })

let cs: { sub: State } = combined(undefined, { type: 'init' })
let cs: RootState = combined(undefined, { type: 'init' })
cs = combined(cs, { type: 'INCREMENT', count: 10 })
cs = combined({ sub: 1 }, { type: 'INCREMENT', count: 10 })

// Combined reducer's state is strictly checked.
// typings:expect-error
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