1import React, { useEffect } from 'react';
2
3export const App: React.FC = () => {
4  
5  useEffect(() => {
6        
7  }, [/*Here can enter some value to call again the content inside useEffect*/])
8  
9  return (
10    <div>Use Effect!</div>
11  );
12}

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

1import React, { useEffect, useState } from 'react';
2import ReactDOM from 'react-dom';
3
4function LifecycleDemo() {
5  // It takes a function
6  useEffect(() => {
7    // This gets called after every render, by default
8    // (the first one, and every one after that)
9    console.log('render!');
10
11    // If you want to implement componentWillUnmount,
12    // return a function from here, and React will call
13    // it prior to unmounting.
14    return () => console.log('unmounting...');
15  }, [ // dependencies to watch = leave blank to run once or you will get a stack overflow  ]);
16
17  return "I'm a lifecycle demo";
18}
19
20function App() {
21  // Set up a piece of state, just so that we have
22  // a way to trigger a re-render.
23  const [random, setRandom] = useState(Math.random());
24
25  // Set up another piece of state to keep track of
26  // whether the LifecycleDemo is shown or hidden
27  const [mounted, setMounted] = useState(true);
28
29  // This function will change the random number,
30  // and trigger a re-render (in the console,
31  // you'll see a "render!" from LifecycleDemo)
32  const reRender = () => setRandom(Math.random());
33
34  // This function will unmount and re-mount the
35  // LifecycleDemo, so you can see its cleanup function
36  // being called.
37  const toggle = () => setMounted(!mounted);
38
39  return (
40    <>
41      <button onClick={reRender}>Re-render</button>
42      <button onClick={toggle}>Show/Hide LifecycleDemo</button>
43      {mounted && <LifecycleDemo/>}
44    </>
45  );
46}
47
48ReactDOM.render(<App/>, document.querySelector('#root'));

1import React, { useState } from 'react';
2function Example() {
3  const [variable, callforupdate] = useState(defaulttwhatever);// <-- this it
4  return (
5    <div></div>
6    );
7}

1import React, { useState } from 'react';
2
3function Example() {
4  	// Declare a new state variable, which we'll call "count"  
5
6	const [count, setCount] = useState(0);
7
8    return (
9      <div>
10        <p>You clicked {count} times</p>
11        <button onClick={() => setCount(count + 1)}>
12          Click me
13        </button>
14      </div>
15    );
16}

1import React, { useState } from 'react';
2
3function Example() {
4  // Declare a new state variable, which we'll call "count"  
5
6  const [count, setCount] = useState(0);
7  return (
8    <div>
9      <p>You clicked {count} times</p>
10      <button onClick={() => setCount(count + 1)}>
11        Click me
12      </button>
13    </div>
14  );
15}