React Hooks

React Hooks are special functions that allow you to use React features like state and lifecycle methods within functional components, without needing to convert them into class components. Introduced in React 16.8, they simplify code and make it easier to manage logic and side effects.

Some popular hooks:

1. useState – Manages state in functional components.
2. useEffect – Handles side effects like fetching data or subscribing to events.
3. useContext – Accesses and shares data across components without prop drilling.
4. useRef – Keeps a reference to DOM elements or values across renders.
5. useReducer – Manages complex state logic similar to Redux reducers.

Hooks make React components more reusable and concise!

React Hooks work by allowing functional components to have features like state and lifecycle methods, which were previously only available in class components. Each hook is essentially a JavaScript function that "hooks" into specific parts of React's internal logic (state, effects, etc.).

Key Principles of Hooks:

1. Only call hooks at the top level: Hooks must be called in the same order every time a component renders, so don't use them inside loops, conditions, or nested functions.
2. Only call hooks from React functions: Hooks can only be used inside functional components or custom hooks, not in regular JavaScript functions.

How Common Hooks Work:

1. useState

• It creates a piece of state inside a functional component.
• It returns an array with two elements: the current state value and a function to update it.

1. useEffect

• Runs side effects after the component renders (e.g., data fetching, setting up subscriptions).
• Can also clean up effects when the component unmounts or before it re-renders.

1. useContext

Accesses values stored in React's Context API, avoiding the need to pass props down through multiple components.

1. useRef

Provides a way to reference DOM elements or persist values between renders without triggering re-renders.

1. useReducer

An alternative to useState for managing more complex state logic, similar to how Redux reducers work.

How it works under the hood:

• Hooks are stateful: React tracks the state of hooks internally via a list for each component. When a component re-renders, React knows which state or effect to retrieve based on the order the hooks are called.
• Efficient updates: React ensures hooks are only re-invoked when necessary (e.g., useEffect only runs if the values in the dependency array change).

This mechanism allows functional components to handle dynamic behavior and lifecycle events as seamlessly as class components!

Custom Hooks:

Custom hooks are functions in React that allow you to reuse logic across multiple components. They encapsulate stateful logic (using built-in hooks like useState, useEffect, etc.) into a function that can be shared between components, making the code cleaner and more reusable.

Why Use Custom Hooks?

1. Code Reusability: Instead of repeating the same logic in multiple components, you can extract it into a custom hook and reuse it.
2. Separation of Concerns: Custom hooks help in organizing and abstracting complex logic out of components, making them simpler to read and maintain.
3. Stateful Logic: They allow you to reuse stateful logic without needing to deal with classes or prop drilling.

How to Create a Custom Hook

A custom hook is simply a function whose name starts with "use". Inside it, you can use React's built-in hooks to manage state, side effects, etc., and return the necessary values or functions for other components to use.

Example: Custom Hook for Fetching Data

import { useState, useEffect } from 'react';

function useFetch(url) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch(url);
        const result = await response.json();
        setData(result);
      } catch (error) {
        setError(error);
      } finally {
        setLoading(false);
      }
    };

    fetchData();
  }, [url]);

  return { data, loading, error };
}

export default useFetch;
        

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import { useState, useEffect } from 'react'; function useFetch(url) { const [data, setData] = useState(null); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { const fetchData = async () => { try { const response = await fetch(url); const result = await response.json(); setData(result); } catch (error) { setError(error); } finally { setLoading(false); } }; fetchData(); }, [url]); return { data, loading, error }; } export default useFetch;

Using the Custom Hook in a Component

function MyComponent() {
  const { data, loading, error } = useFetch('https://api.example.com/data');

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error.message}</p>;

  return (
    <div>
      <h1>Data:</h1>
      <pre>{JSON.stringify(data, null, 2)}</pre>
    </div>
  );
}
        

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function MyComponent() { const { data, loading, error } = useFetch('https://api.example.com/data'); if (loading) return <p>Loading...</p>; if (error) return <p>Error: {error.message}</p>; return ( <div> <h1>Data:</h1> <pre>{JSON.stringify(data, null, 2)}</pre> </div> ); }

Key Points:

• Naming convention: By convention, custom hooks start with use (e.g., useFetch, useAuth).
• Can use other hooks: Inside a custom hook, you can use any of React's built-in hooks (useState, useEffect, useContext, etc.).
• Return values: Custom hooks typically return an object or array with state, functions, or other values that the component using the hook will need.

Custom hooks make your React code more modular, clean, and reusable!