React Hooks

In React, a hook is a special function that allows you to use state and other React features in functional components. Prior to hooks, state and lifecycle methods were only available in class components. Hooks were introduced in React 16.8 to allow functional components to manage state and side effects, making them more powerful and flexible.

Basic Concepts of Hooks

State Hook (useState): Allows you to add state to functional components.

Effect Hook (useEffect): Lets you perform side effects in function components.

Context Hook (useContext): Lets you use context to pass data through the component tree without having to pass props down manually at every level.

Rules of Hooks
  1. Only call hooks at the top level: Don’t call hooks inside loops, conditions, or nested functions. This ensures hooks are called in the same order each time a component renders.
  2. Only call hooks from React functions: Call them from within React functional components or custom hooks, not regular JavaScript functions.
Benefits of Hooks
  1. Simpler Code: Functional components with hooks are generally simpler and easier to read than class components.
  2. Reusability: Hooks allow you to reuse stateful logic across multiple components.
  3. Better Organization: Hooks let you split one component into smaller functions based on what pieces are related (e.g., setting up a subscription or fetching data).
Basic Hooks

useState

The useState hook lets you add state to a functional component. It returns an array with two elements: the current state value and a function to update it.


import React, { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

export default Counter;

useEffect

The useEffect hook lets you perform side effects in function components. It’s similar to lifecycle methods in class components (componentDidMount, componentDidUpdate, componentWillUnmount).


import React, { useState, useEffect } from 'react';

function Example() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    // Update the count
     console.log(`You clicked ${count} times`);
  }, [count]); // Only re-run the effect if count changes

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

export default Example;

useContext

The useContext hook in React allows you to consume context in a functional component without needing to wrap your component in a Consumer component. This makes the code more concise and easier to read. Context provides a way to pass data through the component tree without having to pass props down manually at every level.

Creating and Using Context

  1. Create a Context: Use the createContext function to create a context.
  2. Provide a Context Value: Use a Provider component to pass the context value to the tree.
  3. Consume Context: Use the useContext hook to consume the context value in a functional component.

Step-by-Step Example

Step 1: Create a Context

First, create a context using the createContext function.


import { createContext } from 'react';

// Create a context with 'light' as the default value
const ThemeContext = createContext('light');

export { ThemeContext };

Step 2: Provide a Context Value

Wrap your component tree with a Provider component and pass the context value.


//index.js
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import { ThemeContext } from './ThemeContext';

ReactDOM.render(
  <ThemeContext.Provider value="dark">
    <App />
  </ThemeContext.Provider>,
  document.getElementById('root')
);

Step 3: Consume Context

Use the useContext hook to consume the context value in a functional component.


//ThemedButton.jsx
import React, { useContext } from 'react';
import { ThemeContext } from './ThemeContext';

function ThemedButton() {
  const theme = useContext(ThemeContext);
  return <button style={{ background: theme === 'dark' ? '#333' : '#fff' }}>Themed Button</button>;
}

export default ThemedButton;

App.jsx


import React from 'react';
import ThemedButton from './ThemedButton';

function App() {
  return (
    <div>
      <ThemedButton />
    </div>
  );
}

export default App;