"No overload matches this call" error when setting up ContextApi & useReducer using Typescript

Question

I trying to set up ContextApi & useReducer with typescript. On my "issuesInitialState" variable in useReducer, I get the error:

No overload matches this call. Overload 1 of 5, '(reducer: ({ state, action }: IssueReducer) => {}, initializerArg: never, initializer?: undefined): [never, DispatchWithoutAction]', gave the following error. Argument of type 'IssuesInitialState' is not assignable to parameter of type 'never'. Overload 2 of 5, '(reducer: ({ state, action }: IssueReducer) => {}, initialState: never, initializer?: undefined): [never, Dispatch]', gave the following error. Argument of type 'IssuesInitialState' is not assignable to parameter of type 'never'.ts(2769)

code:

// Store.tsx
type Issue = {
  closeDate: string | null;
  description: string;
  issueId: number;
  lastEditDate: string | null;
  priorityId: string;
  projectId: number;
  reportDate: string;
  statusId: string;
  title: string;
  userId: number;
};

interface IssuesInitialState {
  issues: Issue[];
  issue: Issue;
  issuesByProject: Issue[];
  updateIssue: Issue;
}

const issuesInitialState: IssuesInitialState = {
  issues: [],
  issue: {
    closeDate: "",
    description: "",
    issueId: 0,
    lastEditDate: "",
    priorityId: "",
    projectId: 0,
    reportDate: "",
    statusId: "",
    title: "",
    userId: 0,
  },
  issuesByProject: [],
  updateIssue: {
    closeDate: "",
    description: "",
    issueId: 0,
    lastEditDate: "",
    priorityId: "",
    projectId: 0,
    reportDate: "",
    statusId: "",
    title: "",
    userId: 0,
  },
};

export const IssuesContext = createContext<{
  issuesState: IssuesInitialState;
  issuesDispatch: any;
}>({ issuesState: issuesInitialState, issuesDispatch: () => null });

export function StoreProvider({ children }: any): JSX.Element {
  const [commentsState, commentsDispatch] = useReducer(
    commentsReducer,
    commentsInitialState
  );
  const [issuesState, issuesDispatch] = useReducer(
    issuesReducer,
    issuesInitialState // where the error is!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  );

// IssuesReducer.ts
interface IssueReducer {
  state: IssuesInitialState;
  action: {
    type: string;
    payload: Issue;
  };
}

export const issuesReducer = ({ state, action }: IssueReducer): {} => {
  switch (action.type) {
    case FETCH_ISSUES:

Danita

Answer 1

Besides the return type being an empty object, pointed out by Martin Lockett, your reducer is a function taking a single parameter which is an object with properties state and action, when it should actually be a function that takes 2 parameters, first one being the state and the second being the action. It might help you to type your reducer like so:

import { Reducer } from 'react'

type IssuesAction = {
  type: string;
  payload: Issue;
}

export const issuesReducer: Reducer<IssuesInitialState, IssuesAction> = (state, action) => {
  switch (action.type) {
...

Panier

Answer 2

You have defined your reducer return type as {} which is not compatible with IssuesInitialState as that types' properties are not optional. Define your reducer return type as the state type

Antipater