Working with Custom Hooks

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Custom Hooks allow you to reuse stateful logic across components. They help keep components clean, readable, and maintainable by extracting logic into reusable functions.

What Is a Custom Hook?

• A JavaScript function

• Uses one or more React hooks

• Name must start with use

• Can return values, functions, or objects

Example:

function useCounter() {
  const [count, setCount] = useState(0);
  return { count, setCount };
}

Why Use Custom Hooks?

• Reuse logic across components

• Reduce code duplication

• Separate logic from UI

• Improve readability and testing

Rules of Custom Hooks

Custom hooks follow the same rules as React hooks:

• Call hooks at the top level

• Only call hooks from React functions

• Name must start with use

Creating a Custom Hook

Example: useCounter

import { useState } from "react";

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

  const increment = () => setCount(c => c + 1);
  const decrement = () => setCount(c => c - 1);

  return { count, increment, decrement };
}

export default useCounter;

Using a Custom Hook

import useCounter from "./useCounter";

function Counter() {
  const { count, increment, decrement } = useCounter(10);

  return (
    <>
      <p>{count}</p>
      <button onClick={increment}>+</button>
      <button onClick={decrement}>-</button>
    </>
  );
}

Custom Hook with Side Effects

Example: useFetch

import { useEffect, useState } from "react";

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

  useEffect(() => {
    fetch(url)
      .then(res => res.json())
      .then(data => {
        setData(data);
        setLoading(false);
      });
  }, [url]);

  return { data, loading };
}

Sharing Logic, Not State

Each component using a custom hook gets its own state.

const a = useCounter();
const b = useCounter();

State is not shared unless using Context or Redux.

Custom Hooks vs Utility Functions

Best Practices

• Keep hooks focused on one responsibility

• Return only what’s needed

• Handle cleanup in useEffect

• Place custom hooks in a /hooks folder

Common Use Cases

• API fetching

• Form handling

• Authentication logic

• Window resize / scroll tracking

• Debouncing and throttling

Key Takeaways

• Custom hooks extract reusable logic

• Improve code organization

• Follow hook rules

• Share logic, not UI