React context in client components in NextJS

Introduction

React context lets you share data easily between components without passing props down many levels. It helps keep your app organized and clean.

You want to share user login info across many parts of your app.

You need a theme (like dark or light mode) available everywhere.

You want to manage language settings globally.

You have a shopping cart that many components need to access.

You want to avoid passing props through many layers of components.

Syntax

NextJS

import React, { createContext, useContext, useState } from 'react';

const MyContext = createContext();

function MyProvider({ children }) {
  const [state, setState] = useState();

  return (
    <MyContext.Provider value={{ state, setState }}>
      {children}
    </MyContext.Provider>
  );
}

function MyComponent() {
  const context = useContext(MyContext);
  // use context.state or context.setState
}

createContext makes a new context object.

Provider wraps components that need access to the shared data.

Examples

This example shares a theme string and a way to change it.

NextJS

const ThemeContext = createContext('light');

function ThemeProvider({ children }) {
  const [theme, setTheme] = useState('light');
  return <ThemeContext.Provider value={{ theme, setTheme }}>{children}</ThemeContext.Provider>;
}

function Button() {
  const { theme } = useContext(ThemeContext);
  return <button>{`Current theme is ${theme}`}</button>;
}

This example shares user info and shows a greeting if logged in.

NextJS

const UserContext = createContext(null);

function UserProvider({ children }) {
  const [user, setUser] = useState(null);
  return <UserContext.Provider value={{ user, setUser }}>{children}</UserContext.Provider>;
}

function Profile() {
  const { user } = useContext(UserContext);
  return <div>{user ? `Hello, ${user.name}` : 'Not logged in'}</div>;
}

Sample Program

This is a simple counter app using React context. The count state is shared through context. The button increases the count, and the updated count shows immediately.

NextJS

import React, { createContext, useContext, useState } from 'react';

const CountContext = createContext(0);

function CountProvider({ children }) {
  const [count, setCount] = useState(0);

  return (
    <CountContext.Provider value={{ count, setCount }}>
      {children}
    </CountContext.Provider>
  );
}

function Counter() {
  const { count, setCount } = useContext(CountContext);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increase</button>
    </div>
  );
}

export default function App() {
  return (
    <CountProvider>
      <Counter />
    </CountProvider>
  );
}

Important Notes

Always wrap components that use context inside the matching Provider.

Context is great for global or app-wide data, but avoid overusing it for local state.

In Next.js client components, use 'use client' directive at the top if needed.

Summary

React context shares data easily without passing props everywhere.

Use a Provider to wrap components that need the shared data.

Access context data inside components with useContext hook.

Practice

1. What is the main purpose of React context in client components?

easy

A. To share data easily without passing props through every component

B. To create new HTML elements dynamically

C. To style components with CSS

D. To handle browser events like clicks and scrolls

Solution

1. Step 1: Understand React context role

   React context allows sharing data across components without manually passing props at every level.

2. Step 2: Compare with other options

   Creating HTML elements, styling, and event handling are unrelated to React context's main purpose.

3. Final Answer:

   To share data easily without passing props through every component -> Option A

4. Quick Check:

   React context = data sharing without prop drilling [OK]

Hint: Context shares data without passing props everywhere [OK]

Common Mistakes:

• Confusing context with styling or event handling
• Thinking context creates HTML elements
• Believing context is for CSS only

2. Which of the following is the correct way to access React context in a client component?

easy

A. const value = useRef(MyContext);

B. const value = useState(MyContext);

C. const value = useContext(MyContext);

D. const value = useEffect(MyContext);

Solution

1. Step 1: Identify the hook for context access

   React provides the useContext hook to access context values inside client components.

2. Step 2: Eliminate other hooks

   useState manages state, useEffect handles side effects, and useRef manages references, none access context.

3. Final Answer:

   const value = useContext(MyContext); -> Option C

4. Quick Check:

   useContext hook = context access [OK]

Hint: Use useContext to read context in components [OK]

Common Mistakes:

• Using useState or useEffect instead of useContext
• Trying to access context without a hook
• Confusing useRef with context access

3. Given this code snippet in a Next.js client component:

import { createContext, useContext } from 'react';

const ThemeContext = createContext('light');

export default function DisplayTheme() {
  const theme = useContext(ThemeContext);
  return <div>Current theme: {theme}</div>;
}

What will be displayed if DisplayTheme is rendered without a ThemeContext.Provider?

medium

A. Current theme: undefined

B. Current theme: light

C. Current theme: null

D. Error: Context provider missing

Solution

1. Step 1: Check default context value

   The context is created with default value 'light', so if no Provider wraps the component, this default is used.

2. Step 2: Understand useContext behavior without Provider

   useContext returns the default value when no Provider is found above in the tree.

3. Final Answer:

   Current theme: light -> Option B

4. Quick Check:

   Default context value used without Provider [OK]

Hint: Default context value shows if no Provider wraps component [OK]

Common Mistakes:

• Expecting undefined or null instead of default value
• Thinking it throws an error without Provider
• Confusing default value with null

4. Identify the error in this Next.js client component using React context:

import { createContext, useContext } from 'react';

const UserContext = createContext();

export default function UserName() {
  const user = useContext(UserContext);
  return <div>User: {user.name}</div>;
}

medium

A. UserContext is not wrapped with a Provider, so user is undefined causing error

B. useContext hook is used incorrectly; should pass a string

C. Missing import of React from 'react'

D. Cannot use context inside client components

Solution

1. Step 1: Check context default value and Provider usage

   UserContext is created without a default value and no Provider is shown wrapping UserName, so useContext returns undefined.

2. Step 2: Understand error cause

   Accessing user.name when user is undefined causes a runtime error.

3. Final Answer:

   UserContext is not wrapped with a Provider, so user is undefined causing error -> Option A

4. Quick Check:

   Undefined context value causes error accessing properties [OK]

Hint: Always wrap context consumers with Provider to avoid undefined errors [OK]

Common Mistakes:

• Assuming useContext needs a string argument
• Forgetting to wrap with Provider
• Thinking React import is mandatory in Next.js 13+ client components

5. You want to create a theme toggle in a Next.js client component using React context. Which approach correctly updates the theme value across components?

hard

A. Pass theme as a prop to every component without using context

B. Create ThemeContext with a fixed string; update theme by changing the string directly in components

C. Use useState inside each component separately without context to manage theme

D. Create a ThemeContext with state and provide toggle function via Provider; use useContext to read and update theme

Solution

1. Step 1: Understand state sharing with context

   To update theme globally, context must provide state and a function to toggle it, so all components share and update the same state.

2. Step 2: Evaluate other options

   Fixed string cannot update dynamically; separate useState per component does not share state; passing props everywhere defeats context purpose.

3. Final Answer:

   Create a ThemeContext with state and provide toggle function via Provider; use useContext to read and update theme -> Option D

4. Quick Check:

   Context with state and updater shares dynamic data [OK]

Hint: Use context Provider with state and updater for shared dynamic data [OK]

Common Mistakes:

• Trying to update fixed context value directly
• Using separate state in each component without sharing
• Passing props everywhere instead of using context