day-2-react js
Published: 2023-01-11 17:57:44

DATA

```
export const data = [
  { id: 1, name: 'john' },
  { id: 2, name: 'peter' },
  { id: 3, name: 'susan' },
  { id: 4, name: 'anna' },
];
```
**USE STATE**

- // starts with use
- // component must be uppercase
- // invoke inside function/component body
- // don't call hooks conditonally_

```
import React, { useState } from 'react';

const UseStateBasics = () => {
  // console.log(useState());
  // const value = useState()[0];
  // const handler = useState()[1];
  // console.log(value, handler);

  const [text, setText] = useState('random title');
  const handleClick = () => {
    if (text === 'random title') {
      setText('hello world');
    } else {
      setText('random title');
    }
  };

  return (
    <React.Fragment>
      <h1>{text}</h1>
      <button type='button' className='btn' onClick={handleClick}>
        change title
      </button>
    </React.Fragment>
  );
};

export default UseStateBasics;
```
-useState array

```
import React from 'react';
import { data } from '../../../data';
const UseStateArray = () => {
  const [people, setPeople] = React.useState(data);

  const removeItem = (id) => {
    let newPeople = people.filter((person) => person.id !== id);
    setPeople(newPeople);
  };
  return (
    <>
      {people.map((person) => {
        const { id, name } = person;
        return (
          <div key={id} className='item'>
            <h4>{name}</h4>
            <button onClick={() => removeItem(id)}>remove</button>
          </div>
        );
      })}
      <button className='btn' onClick={() => setPeople([])}>
        clear items
      </button>
    </>
  );
};

export default UseStateArray;

```
-useState object

```
import React, { useState } from 'react';

const UseStateObject = () => {
  const [person, setPerson] = useState({
    name: 'peter',
    age: 24,
    message: 'random message',
  });

  // const [name,setName] = useState('peter')
  // const [age,setAge] = useState(24)
  // const [message,setMessage] = useState('random message')

  const changeMessage = () => {
    setPerson({ ...person, message: 'hello world' });
    // setMessage('hello world')
  };

  return (
    <>
      <h3>{person.name}</h3>
      <h3>{person.age}</h3>
      <h4>{person.message}</h4>
      <button className='btn' onClick={changeMessage}>
        change message
      </button>
    </>
  );
};

export default UseStateObject;

```
-useState counter

```
import React, { useState } from 'react';

const UseStateCounter = () => {
  const [value, setValue] = useState(0);

  const reset = () => {
    setValue(0);
  };

  const complexIncrease = () => {
    setTimeout(() => {
      // setValue(value + 1);
      setValue((prevState) => {
        return prevState + 1;
      });
    }, 2000);
  };

  return (
    <>
      <section style={{ margin: '4rem 0' }}>
        <h2>regular counter</h2>
        <h1>{value}</h1>
        <button className='btn' onClick={() => setValue(value - 1)}>
          decrease
        </button>
        <button className='btn' onClick={reset}>
          reset
        </button>
        <button className='btn' onClick={() => setValue(value + 1)}>
          increase
        </button>
      </section>
      <section style={{ margin: '4rem 0' }}>
        <h2>more complex counter</h2>
        <h1>{value}</h1>
        <button className='btn' onClick={complexIncrease}>
          increase later
        </button>
      </section>
    </>
  );
};

export default UseStateCounter;

```