How to set the type of a function parameter?

Question

typescript

[CHANGE_THEME]: (state: stateProps, { payload }): stateProps => ({
    ...state,
    ...payload,
  }),

How to set payload type?

Answer 1

It can be like this -

interface StateProps {
    a: number;
    b: string;
    c: boolean;
}

interface Action<P> {
    payload: Partial<P>;
}

const f = <P>(state: P, { payload }: Action<P>): P => ({
    ...state,
    ...payload,
});

let nextState = f(
    { a: 0, b: '', c: true },
    { payload: { c: false } }
);

The only thing to remember is that generic functions are not valid constructs in files with the .tsx.