Introducing Hooks

Hooks in React JS are a new addition in Version 16.8. They let you use state and other React features without writing a class.

Example:

import React, { useState }  from 'react'

function HookEx1() {
     // Declare a new state variable, which we'll call "count"
     const [count, setCount] = useState(0);
    return (
        <div>
            <p>You clicked {count} times</p>
            <button onClick={() => setCount(count + 1)}>Click me</button>
        </div>
    )
}

export default HookEx1

This new function useState is the first “Hook” . When you click the button, it increments the value.

useState is a Hook. We call it inside a function component to add some local state to it. React will preserve this state between re-renders. useState returns a pair: the current state value and a function that lets you update it. You can call this function from an event handler or somewhere else. It’s similar to this.setState in a class, except it doesn’t merge the old and new state together.

Equivalent Class Example

If you used classes in React before, this code should look familiar:

class HookEx1 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>
    );
  }
}

What’s a Hooks in React JS ?

Our new example starts by importing the useState Hook from React:

import React, { useState } from 'react';

function Example() {
  // ...
}

What is a Hook? A Hook is a special function that lets you “hook into” React features. For example, useState is a Hook that lets you add React state to function components. We’ll learn other Hooks later.

When would I use a Hook? If you write a function component and realize you need to add some state to it, previously you had to convert it to a class. Now you can use a Hook inside the existing function component. We’re going to do that right now!