State management with Next.js and React

Published May 15, 2022・Last updated December 16, 2024・2 min read

The global state can be helpful when components share some common parts. Also, some parts can stay persistent (in local storage) and be used in the following user's session. React provides a native way to handle state management using context with the hooks.

Usage

// ...
import { useAppContext } from 'context';
import { UPDATE_FEATURE_ACTIVATION } from 'context/constants';
export function CustomComponent() {
  const { state, dispatch } = useAppContext();
  // get value from the store
  console.log(state.isFeatureActivated);
  // dispatch action to change the state
  dispatch({
    type: UPDATE_FEATURE_ACTIVATION,
    payload: { isFeatureActivated: true }
  });
  // ...
}

Context setup

// context/index.jsx
import PropTypes from 'prop-types';
import React, {
  createContext,
  useContext,
  useEffect,
  useMemo,
  useReducer
} from 'react';
import { getItem, setItem, STATE_KEY } from 'utils/local-storage';
import { INITIALIZE_STORE } from './constants';
import { appReducer, initialState } from './reducer';
const appContext = createContext(initialState);
export function AppWrapper({ children }) {
  const [state, dispatch] = useReducer(appReducer, initialState);
  const contextValue = useMemo(() => {
    return { state, dispatch };
  }, [state, dispatch]);
  useEffect(() => {
    const stateItem = getItem(STATE_KEY);
    if (!stateItem) return;
    const parsedState = JSON.parse(stateItem);
    const updatedState = {
      ...initialState,
      // persistent state
      isFeatureActivated: parsedState.isFeatureActivated
    };
    dispatch({
      type: INITIALIZE_STORE,
      payload: updatedState
    });
  }, []);
  useEffect(() => {
    if (state !== initialState) {
      setItem(STATE_KEY, JSON.stringify(state));
    }
  }, [state]);
  return (
    <appContext.Provider value={contextValue}>{children}</appContext.Provider>
  );
}
AppWrapper.propTypes = {
  children: PropTypes.oneOfType([PropTypes.array, PropTypes.object]).isRequired
};
export function useAppContext() {
  return useContext(appContext);
}

Reducer with actions

// context/reducer.js
import { INITIALIZE_STORE, UPDATE_FEATURE_ACTIVATION } from './constants';
export const initialState = {
  isFeatureActivated: false
};
export const appReducer = (state, action) => {
  switch (action.type) {
    case INITIALIZE_STORE: {
      return action.payload;
    }
    case UPDATE_FEATURE_ACTIVATION: {
      return {
        ...state,
        isFeatureActivated: action.payload.isFeatureActivated
      };
    }
    default:
      return state;
  }
};

Wrapper around the app

// app/layout.jsx
import { AppContextProvider } from 'context';
export default function RootLayout({ children }) {
  return (
    <html lang="en">
      <head>// ...</head>
      <body>
        <AppContextProvider>{children}</AppContextProvider>
      </body>
    </html>
  );
}

Constants

// context/constants.js
export const INITIALIZE_STORE = 'INITIALIZE_STORE';
export const UPDATE_FEATURE_ACTIVATION = 'UPDATE_FEATURE_ACTIVATION';

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