Context provider in React - Mini Project: Build & Apply

Using a Context Provider in React

📖 Scenario: You are building a simple React app that shares a theme color across multiple components without passing props manually.

🎯 Goal: Create a React context provider to share a theme color string with child components.

📋 What You'll Learn

Create a React context with a default value

Create a provider component that uses the context

Use the provider to wrap child components

Consume the context value inside a child component

💡 Why This Matters

🌍 Real World

Context providers help share data like themes, user info, or language settings across many components without passing props manually.

💼 Career

Understanding React context is essential for building scalable React apps and working on modern frontend projects.

1

Create a React context with default value

Create a React context called ThemeContext with the default value 'light'.

React

import React from 'react';

// Create ThemeContext with default value 'light'
// Your code here

Hint

Use React.createContext and pass the string 'light' as the default value.

2

Create a ThemeProvider component

Create a functional component called ThemeProvider that returns ThemeContext.Provider wrapping children and passes the value 'dark' to the provider.

React

import React from 'react';

const ThemeContext = React.createContext('light');

// Create ThemeProvider component that uses ThemeContext.Provider
// Your code here

Hint

Use a function component with { children } props and return ThemeContext.Provider with value="dark".

3

Use ThemeProvider to wrap App component

Create a functional component called App that returns ThemeProvider wrapping a Content component.

React

import React from 'react';

const ThemeContext = React.createContext('light');

function ThemeProvider({ children }) {
    return {children};
}

// Create App component that uses ThemeProvider to wrap Content
// Your code here

Hint

Wrap the Content component inside ThemeProvider in the App component.

4

Consume context value inside Content component

Inside the Content component, use React.useContext with ThemeContext to get the theme value, then return a div that displays the text Current theme: followed by the theme value.

React

import React from 'react';

const ThemeContext = React.createContext('light');

function ThemeProvider({ children }) {
    return {children};
}

function Content() {
    // Use React.useContext to get theme
    // Your code here
}

function App() {
    return ;
}

Hint

Call React.useContext(ThemeContext) to get the theme value and display it inside a div.

Practice

1. What is the main purpose of a Context.Provider in React?

easy

A. To share data with all components inside its tree without passing props manually

B. To create a new React component

C. To handle component state locally

D. To style components globally

Solution

1. Step 1: Understand what Context.Provider does

   It allows sharing data to all nested components without passing props down manually.

2. Step 2: Compare options

   Only To share data with all components inside its tree without passing props manually describes this sharing behavior correctly; others describe unrelated tasks.

3. Final Answer:

   To share data with all components inside its tree without passing props manually -> Option A

4. Quick Check:

   Context.Provider shares data = A [OK]

Hint: Context.Provider shares data down component tree [OK]

Common Mistakes:

• Thinking Provider creates components
• Confusing Provider with state management
• Assuming Provider styles components

2. Which of the following is the correct way to create a context and provide a value in React?

easy

A. const MyContext = React.createContext(); ...

B. const MyContext = React.useContext(); ...

C. const MyContext = React.createProvider(); ...

D. const MyContext = React.createContext(); ...

Solution

1. Step 1: Identify correct context creation method

   React.createContext() is the correct method to create a context.

2. Step 2: Confirm correct usage of Provider

   Provider uses a value prop to share data; Consumer does not accept value prop directly.

3. Final Answer:

   const MyContext = React.createContext(); <MyContext.Provider value={data}>...</MyContext.Provider> -> Option D

4. Quick Check:

   createContext + Provider with value = D [OK]

Hint: Use React.createContext() and Provider with value prop [OK]

Common Mistakes:

• Using React.useContext() to create context
• Trying React.createProvider() which doesn't exist
• Passing value to Consumer instead of Provider

3. Given the code below, what will be rendered inside DisplayUser component?

const UserContext = React.createContext();

function DisplayUser() {
  const user = React.useContext(UserContext);
  return <div>Hello, {user.name}!</div>;
}

function App() {
  return (
    <UserContext.Provider value={{ name: 'Alice' }}>
      <DisplayUser />
    </UserContext.Provider>
  );
}

medium

A. Hello, undefined!

B. Error: useContext must be inside a Provider

C. Hello, Alice!

D. Hello, {user.name}!

Solution

1. Step 1: Check Provider value

   The Provider passes an object with name 'Alice' as value.

2. Step 2: useContext reads the value

   DisplayUser uses useContext to get the user object and accesses user.name which is 'Alice'.

3. Final Answer:

   Hello, Alice! -> Option C

4. Quick Check:

   useContext reads Provider value = B [OK]

Hint: useContext gets value from nearest Provider [OK]

Common Mistakes:

• Assuming useContext returns undefined without Provider
• Thinking useContext returns the whole context object, not value
• Confusing JSX output with raw code

4. Identify the error in the following React code using Context Provider:

const ThemeContext = React.createContext();

function App() {
  return (
    <ThemeContext.Provider>
      <Content />
    </ThemeContext.Provider>
  );
}

function Content() {
  const theme = React.useContext(ThemeContext);
  return <div>Theme is {theme}</div>;
}

medium

A. Provider is missing the required value prop

B. useContext is used incorrectly outside Provider

C. ThemeContext should be created with React.useContext()

D. Content component should not use useContext

Solution

1. Step 1: Check Provider usage

   The Provider must have a value prop to supply data to consumers.

2. Step 2: Identify missing value prop

   In the code, <ThemeContext.Provider> lacks value, so useContext gets undefined.

3. Final Answer:

   Provider is missing the required value prop -> Option A

4. Quick Check:

   Provider needs value prop = C [OK]

Hint: Provider always needs a value prop [OK]

Common Mistakes:

• Forgetting to pass value to Provider
• Confusing createContext with useContext
• Thinking useContext can't be inside Provider tree

5. You want to share a user object and a function to update it across many components using React Context. Which approach correctly combines these in a single context provider?

hard

A. Create two separate contexts, one for user and one for setUser; use two Providers

B. Create context with React.createContext(); provide value={{ user, setUser }}; consume with useContext

C. Pass user as value and call setUser directly inside components without context

D. Use useState inside each component instead of context

Solution

1. Step 1: Understand combining data and updater in context

   Context value can be an object holding both user data and setUser function.

2. Step 2: Confirm correct usage

   Providing value={{ user, setUser }} allows any component to read user and update it via setUser.

3. Final Answer:

   Create context with React.createContext(); provide value={{ user, setUser }}; consume with useContext -> Option B

4. Quick Check:

   Combine data and updater in one context value = A [OK]

Hint: Put data and updater together in context value object [OK]

Common Mistakes:

• Creating multiple contexts unnecessarily
• Calling setUser without context
• Using local state instead of shared context