A Guide to React Custom Hooks

#react #hook #javascript #webdev

Custom Hooks in React are a powerful feature that allows us to extract component logic into reusable functions. These Hooks are JavaScript functions that can use other Hooks provided by React. They enable us to organize logic into separate, reusable modules.

📌 Table of Contents

Prerequisites
Our First Custom Hook
Tips for Building Custom Hooks
Sharing Logic with Custom Hooks
- Building a Data Fetching Hook
- Building a Form Handling Hook
Wrapping Up

Prerequisites

Before diving into custom Hooks, it's important to have a basic understanding of React and its core concepts, such as components, state, and built-in Hooks like useState and useEffect.

Our First Custom Hook

Let's start by creating a simple custom Hook. We’ll build a useCounter hook that encapsulates the logic for incrementing a counter.

import { useState } from 'react'

// Custom hook for counter functionality
function useCounter(initialValue = 0) {
  const [count, setCount] = useState(initialValue) // State to keep track of count

  // Function to increment count
  const increment = () => setCount(prevState => prevState + 1)

  // Returns count and increment function
  return [count, increment]
}

To use our useCounter Hook, we can include it in a functional component:

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

// Component using the useCounter Hook
function CounterComponent() {
  const [count, increment] = useCounter() // Utilizing useCounter

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={increment}>Increment</button>
    </div>
  )
}

Tips for Building Custom Hooks

Start by identifying repetitive logic across your components.
Extract this logic into a function named with use prefix. Custom hooks should start with use, like useFormInput or useFetch.
Use React's built-in Hooks within your custom Hook as needed.
Return anything that will be useful for the component using this Hook.
Each custom hook should be responsible for a single piece of functionality.

Sharing Logic with Custom Hooks

Custom Hooks are excellent for sharing logic across multiple components. In this section, we will create two common custom hooks that React developers often create to share logic across multiple components.

Building a Data Fetching Hook

If we need to fetch data from an API in several components, we can create a useFetch Hook. Here's a simple implementation of useFetch:

import { useState, useEffect } from 'react'

// Custom hook for fetching data
function useFetch(url) {

  const [data, setData] = useState(null) // State for data
  const [loading, setLoading] = useState(true) // State for loading
  const [error, setError] = useState(null) // State for error handling

  useEffect(() => {
    const fetchData = async () => {
      setLoading(true)
      setError(null)

      try {
        const response = await fetch(url)

        if (!response.ok) {
          throw new Error(`An error occurred: ${response.statusText}`)
        }

        const jsonData = await response.json()
        setData(jsonData)
      } catch (error) {
        setError(error.message)
      } finally {
        setLoading(false)
      }
    }

    fetchData()
  }, [url]) // Dependency array with url

  return { data, loading, error }
}

We can now use this Hook in our components to fetch data easily:

import React from 'react'
import useFetch from './useFetch'

// Component using the useFetch Hook
function DataDisplayComponent({ url }) {
  const { data, loading, error } = useFetch(url) // Utilizing useFetch

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

  return <div>{JSON.stringify(data, null, 2)}</div>
}

Building a Form Handling Hook

Handling forms in React can be verbose. A custom hook, useForm, can simplify this. Here’s how we might structure it:

import { useState } from 'react'

function useFormInput(initialValue) {
  const [value, setValue] = useState(initialValue)

  const handleChange = (e) => {
    setValue(e.target.value)
  }

  // Returns an object with value and onChange properties
  return {
    value,
    onChange: handleChange
  }
}

We can now use this Hook in our form related components:

import React from 'react'
import useFormInput from './useFormInput'

function FormComponent() {

  const name = useFormInput('')
  const age = useFormInput('')

  const handleSubmit = (e) => {
    e.preventDefault()
    console.log(`Name: ${name.value}, Age: ${age.value}`)
  }

  return (
    <form onSubmit={handleSubmit}>
      <div>
        <label>
          Name:
          {/* The spread operator here is equivalent to value={name.value} onChange={name.onChange} */}
          <input type="text" {...name} />
        </label>
      </div>
      <div>
        <label>
          Age:
          <input type="number" {...age} />
        </label>
      </div>
      <button type="submit">Submit</button>
    </form>
  )
}

💡 The implementation of useFormInput provided here is a basic version, designed for straightforward form input management. If additional functionalities are required, such as form validation or handling more complex form patterns, the Hook should be further customized and extended.

Wrapping Up

Custom Hooks in React offer a powerful and elegant way to reuse and share logic across components. By understanding and leveraging this feature, we can significantly simplify our components and improve our code's maintainability and readability.

Demo | Documentation

Top comments (8)

Rense Bakker • Nov 21 '23

If you build custom hooks, its very important to memoize everything that you return from that hook. For example the increment function should be wrapped in a useCallback. Otherwise any side effect or child component that uses the values returned by the hook, will always trigger on every rerender, even if the values didn't really change.

Rasaf Ibrahim • Nov 21 '23

Thanks for your insights on memoizing in custom hooks. You're spot on about the importance of using useCallback for functions like increment to prevent unnecessary re-renders in certain scenarios, such as when passing callbacks to child components or using them as dependencies in useEffect.

However, it's also important to consider that memoization isn't always necessary and can sometimes add complexity. While it's crucial in cases like callback functions, over-memoizing can lead to performance overhead. It's about finding the right balance based on the specific use case. Your point is well-taken and reminds us to thoughtfully consider when and how to apply memoization effectively.