Hooks introduces State and Lifecycle Methods to function-based components.

Hooks make it really easy to share logic between components.

// components/App.js
import React from 'react';

export default App extends React.Component {
    state = {
        counter: 0
    }

    handleClick = () => this.setState({counter: this.state.counter++})

    render() {
        return <div>
            <button onClick={this.handleClick}>{this.state.counter}</button>
        </div>
    }
}
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// components/App.js
import React, { useState, useEffect } from "react";

const App = () => {
  const [counter, setCounter] = useState(0);

  const updateCounter = () => setCounter(counter++);

  useEffect(() => {
    console.log("Counter updated!");
  }, [counter]);

  return (
    <div>
      <button onClick={updateCounter}>{counter}</button>
    </div>
  );
};
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useEffect allows us to effectively use a combined version of componentDidMount and componentDidUpdate.

Notes:

import React, { useEffect } from "react";

// second argument controls whether or not the arrow function is called
useEffect(() => {
  console.log("Counter updated!");
}, [counter]);
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Believe it or not, what we can actually do is abstract the useEffect outside of the function component.

This is incredibly useful to create reuseable effects.