use effect react

1  useEffect(() => {
2	
3  },[]);

1  useEffect(() => {
2	//your code goes here
3    return () => {
4      //your cleanup code codes here
5    };
6  },[]);

1function App() {
2  const [count, setCount] = useState(0);
3
4  useEffect(() => {
5    longResolve().then(() => {
6      alert(count);
7    });
8  }, []);
9
10  return (
11    <div>
12      <button
13        onClick={() => {
14          setCount(count + 1);
15        }}
16      >
17        Count: {count}
18      </button>
19    </div>
20  );
21}

1useEffect(() => {
2	//  code goes here
3    return () => {
4      // cleanup code codes here
5    };
6  },[]);

1import React, { useState, useEffect } from 'react';
2function Example() {
3  const [count, setCount] = useState(0);
4
5  useEffect(() => {    document.title = `You clicked ${count} times`;  });
6  return (
7    <div>
8      <p>You clicked {count} times</p>
9      <button onClick={() => setCount(count + 1)}>
10        Click me
11      </button>
12    </div>
13  );
14}

1class Example extends React.Component {
2  constructor(props) {
3    super(props);
4    this.state = {
5      count: 0
6    };
7  }
8
9  componentDidMount() {    document.title = `You clicked ${this.state.count} times`;  }  componentDidUpdate() {    document.title = `You clicked ${this.state.count} times`;  }
10  render() {
11    return (
12      <div>
13        <p>You clicked {this.state.count} times</p>
14        <button onClick={() => this.setState({ count: this.state.count + 1 })}>
15          Click me
16        </button>
17      </div>
18    );
19  }
20}