Introduction
Hooks are a new feature introduced in React16.8.
I'll try to explain what they are in the following order.
What are Hooks?
According to the official React documentation,
Hooks let you use state and other React features without writing a class.
Yup. That's exactly it!.
Now you can use some React features such as state in functional components thanks to hooks!!
I'll introduce 3 following hooks in this post.
- (1)State Hook: It lets you use
stateandsetStatein functional components. - (2)Effect Hook: It lets you perform side effects such as data fetching in functional components.
- (3)Custom Hooks: Building your custom hooks lets you extract component logic into reusable functions.
Rules of Hooks
There are 2 ground rules you have to follow to use hooks safely.
(1) Only Call Hooks at the Top Level!!
Don’t call Hooks inside loops, conditions, or nested functions.
(2) Only Call Hooks from React Functions!!
Don’t call Hooks from regular JavaScript functions.
State Hook
You can use state and setState in functional components by using a hook called useState.
Let's see how to use useState through comparing a functional componentusing useState to the equivalent class component.
Equivalent Class Component
It does the following 2 things.
- (1) Define the
countstate and its initialState0. - (2) Add 1 to
counteach time setState is called.
class Example extends React.Component {
constructor(props) {
super(props);
this.state = {
count: 0
};
}
render() {
return (
<div>
<p>You clicked{this.state.count} times</p>
<button onClick={() => this.setState({ count: this.state.count + 1 })}>
Click Me
</button>
</div>
);
}
}
Functional Component with State Hook
Now it's time to create a functional component using useState which does the same thing as the class component above.
The basic syntax of useState looks like this!
const [state, setState] = useState(initialState);
It's like you define the state, setState and initialState all together.
If you want to define the same state as the one in the class component above, it would look like this.
import React, { useState } from 'react';
function Counter() {
const [count, setCount] = useState(0)
}
Notice 3 things in the code above!
- (1)
countis the equivalent ofthis.state={count:0}in the class component. - (2)
setCountis the equivalent ofsetStatepart in the class component. - (3)
0is the initial state ofcount.
While you are writing up the rest of the code, keep these 2 things in mind.
- (1) You can use
countdirectory!(no need to dothis.count.) - (2) You can update the state by using
setCount.
import React, { useState } from 'react';
function Counter() {
const [count, setCount] = useState(0)
return(
<div>
// (1) You can use count directory!
<p>You clicked {count} times</p>
// (2) You can update the state by using setCount.
<button onClick={() => setCount(count + 1)}> Click me</button>
</div>
)
}
export default Counter;
As a side note, you can define multiple states like the code below.
import React, { useState } from 'react';
function Counter() {
const [count, setCount] = useState(0)
const [name, setName] = useState('')
return(
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}> Click me</button>
<p>My name is {name}.</p>
<button onClick={() => setName('テスト太郎')}>Show my name</button>
</div>
)
}
export default Counter;
Effect Hook
You can perform side effects in functional components by using a hook called useEffect!
Let's see how to use useEffec through comparing a functional componentusing useEffect to the equivalent class component.
Example Class Component
In class components, we perform side effects such as fetching data and changing the DOM in componentDidMount componentDidUpdate.
Here, it outputs It did mount in the console after a component is mounted and outputs It did get updated after updating occurs.
import React from 'react';
class Effect extends React.Component {
constructor(props) {
super(props);
this.state = {
count: 0
};
}
componentDidMount() {
console.log('It did mount.')
}
componentDidUpdate() {
console.log('It did get updated.')
}
render() {
return (
<div>
<h1>You clicked {this.state.count} times</h1>
<button onClick={() => this.setState({ count: this.state.count + 1 })}>
Click me
</button>
</div>
);
}
}
Example Functional Component using useEffect
The useEffect hook is like a combination of componentDidMount, componentDidUpdate and componentWillUnmount.
It runs after every render including the first render.
When you are building react applications with hooks this is where you perform side effects.
import React, { useState, useEffect } from 'react'
function Effect() {
const [count, setCount] = useState(0)
useEffect(() => {
console.log('It got rendered')
})
return(
<div>
<h1>You clicked {count} times</h1>
<button onClick={() => setCount(count + 1)}> Click me</button>
</div>
);
}
Custom Hooks
As I mentioned above, building your custom hooks lets you extract component logic into reusable functions.
Let's suppose there are two components like below.
- (1) A component called
Statuswhich returnsLogged inif it receivesid = 1. - (2) A component called
Messagewhich returnsWelocme Backif it receivesid = 1.
export default function Status(props){
const [isLoggedIn, setIsLoggedIn] = useState(false);
const handleStateChange = (id) => {
if(id === 1){
setIsLoggedIn(true)
}
else{
setIsLoggedIn(false)
}
}
useEffect(() => {
handleStateChange(props.user.id)
})
const status = isLoggedIn ? 'Logged in' : 'Sign up'
return (
<>
<h1>Status: {status}</h1>
</>
)
}
export default function Message(props){
const [isLoggedIn, setIsLoggedIn] = useState(false);
const handleStateChange = (id) => {
if(id === 1){
setIsLoggedIn(true)
}
else{
setIsLoggedIn(false)
}
}
useEffect(() => {
handleStateChange(props.user.id)
})
const message = isLoggedIn ? 'Welcome Back' : 'Who are you??'
return (
<>
<h1>Message: {message}</h1>
</>
)
}
As you probably noticed, it's very redundant.
You can build a custom hook to extract the same logic exists in both components into one reusable function.
※It is very important that you name your custom hook starting with use.
In this case, I named my custom hook useLogIn.
import { useState, useEffect } from 'react';
export default function useLogIn(userId){
const [isLoggedIn, setIsLoggedIn] = useState(false);
// The login you want to reuse.
const handleStateChange = (id) => {
if(id === 1){
setIsLoggedIn(true)
}
else{
setIsLoggedIn(false)
}
}
// Perform side effects in useEffect.
useEffect(() => {
handleStateChange(userId)
})
return isLoggedIn;
}
Using useLogIn, we can simplify Status and Message components.
import React from 'react';
import useLogIn from './useLogIn';
export default function Status(props){
const status = useLogIn(props.user.id) ? 'Logged in' : 'Sign up'
return (
<>
<h1>Status: {status}</h1>
</>
)
}
import React from 'react';
import useLogIn from './useLogIn';
export default function Message(props){
const message = useLogIn(props.user.id) ? 'Welcome Back' : 'Who are you??'
return (
<>
<h1>Message: {message}</h1>
</>
)
}
The custom hooks can be used for other cool stuff, check out the official document about Building Your Own Hooks.
Top comments (11)
To run the code in Java, you must first create a class. I'm not sure what this Hook technique is all about. I'm working on an application for my Malaysian customer of Transfer Factor Malaysia. I'm completely baffled as to how to do this approach. I attempted it without first establishing a class. Errors were still present.
The new feature in the react 16.8 version, it is used to allow and use state and other features of React with out writing or giving a class. I have experienced this when I used this to my site perfectcvmaker.ae last month and it is great and easy to make.
These are extraordinary in light of the fact that going out as a family can be very costly, particularly at the motion pictures where food and beverages are difficult to bear on an ordinary financial plan. By : UK Essay Writing Service.
Many early birds have already started using this custom hooks library
in their ReactJs/NextJs project.
Have you started using it?
scriptkavi/hooks
PS: Don't be a late bloomer :P
Java always requires a class to run the code. I didn’t get a clear concept of this Hook method. I am developing an application for my client cv help uk - cvwritings.co.uk. I am totally getting confused about how to run this method. I’ve tried it without creating a class. It was still showing errors.
It's a new feature in React that allows you to leverage state and other React capabilities without having to write or give a class. Last month, I utilised this on my best travel company site, and it worked excellent and was simple to set up.
Simple and succinct. Well done!
Solary Electricals is a leading auto body collision repair welding products company committed to deliver innovation as well as powerful, durable and reliable products. Browse Solary's spot welder, dent puller, infrared curing lamp, hot stapler, battery charger and more for all your auto body repair needs.
The best thing is that the custom hooks can be used for other cool stuff. Thanks for sharing this guide. This will be helpful for me to serve the animation production service all over the region.
Thank's for sharing. I didn't understand the hook method clearly. I am currently developing an application for my my friend wikiwriters.co.uk | Wikipedia agency in UK. Your info helped me solve some major technical issues. Thank you!