Using react context with react hooks in typescript

Question

Code below demonstrates how I'm trying to implement react's context with react hooks, idea here is that I will be able to easily access context from any child component like this

const {authState, authActions} = useContext(AuthCtx);

To begin with I create a file that exports context and provider.

import * as React from 'react';

const { createContext, useState } = React;

const initialState = {
  email: '',
  password: ''
};

const AuthCtx = createContext(initialState);

export function AuthProvider({ children }) {
  function setEmail(email: string) {
    setState({...state, email});
  }

  function setPassword(password: string) {
    setState({...state, password}); 
  }

  const [state, setState] = useState(initialState);
  const actions = {
    setEmail,
    setPassword
  };

  return (
    <AuthCtx.Provider value={{ authState: state, authActions: actions }}>
      {children}
    </AuthCtx.Provider>
  );
}

export default AuthCtx;

This works, but I get error below in value of provider, probably because I add actions in, hence the question, is there a way for me to keep everything typed and still be able to export context and provider?

I beliebe I also can't place createContext into my main function since it will re-create it all the time?

[ts] Type '{ authState: { email: string; password: string; }; authActions: { setEmail: (email: string) => void; setPassword: (password: string) => void; }; }' is not assignable to type '{ email: string; password: string; }'. Object literal may only specify known properties, and 'authState' does not exist in type '{ email: string; password: string; }'. [2322] index.d.ts(266, 9): The expected type comes from property 'value' which is declared here on type 'IntrinsicAttributes & ProviderProps<{ email: string; password: string; }>' (property) authState: { email: string; password: string; }

@ShubhamKhatri by default it inherits it from `createContext(initialState)` issue is that creation is outside of function, hence I can't type actions I think. And I need those actions inside my function component as they update state. If I move context inside the function, I can easily type actions, but no longer export context and I think there will be complications since react function components are re-ran on each render — Ilja, Nov 16 '18 at 10:45

Роман Татаринов · Answer 1 · 2020-06-22T13:30:48.887

Answer above works, because strict rules of checking of types disabled. Example for context with strict rules:

import { createContext, Dispatch, SetStateAction, useState } from 'react';
import { Theme } from '@styles/enums';
import { Language } from '@common/enums';

type Props = {
  children: React.ReactNode;
};

type Context = {
  appLang: string;
  appTheme: string;
  setContext: Dispatch<SetStateAction<Context>>;
};

const initialContext: Context = {
  appLang: Language.EN,
  appTheme: Theme.DEFAULT,
  setContext: (): void => {
    throw new Error('setContext function must be overridden');
  },
};

const AppContext = createContext<Context>(initialContext);

const AppContextProvider = ({ children }: Props): JSX.Element => {
  const [contextState, setContext] = useState<Context>(initialContext);

  return (
    <AppContext.Provider value={{ ...contextState, setContext }}>
      {children}
    </AppContext.Provider>
  );
};

export { AppContext, AppContextProvider };

It works for me. Theme and Language it just enums, like this:

export enum Theme {
  DEFAULT = 'DEFAULT',
  BLACK = 'BLACK',
}

And I send Error function in setContext inner initialContext for throwing error if programmer doesn't define setContext in Provider. You can just use

setContext: (): void => {}

Good luck!

score 15 · Accepted Answer · edited Jun 23 '20 at 21:19

15

While creating Context, you are providing an initial value to it. Provide it in the same format as you expect it to be for the Provider like:

const initialState = {
  authState : { 
      email: '',
      password: ''
  },
  authActions = {
    setEmail: () => {},
    setPassword: () => {}
  };
};

const AuthCtx = createContext(initialState);

Also, you don't even need the initialState since its only passed to Consumer, if you don't have a Provider higher up in the hierarchy for the Consumer.

edited Jun 23 '20 at 21:19

jdhurst

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answered Nov 16 '18 at 10:50

Shubham Khatri

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2

when i use usestate in my context i see this error .Type 'Dispatch' is not assignable to type '() => void – Mehran Motiee Jul 24 '19 at 07:40

Using react context with react hooks in typescript

2 Answers2