JAVASCRIPT

react usestate

import React, { useState } from 'react'
import { render } from 'react-dom'

const randomDiceRoll = () => {
  return Math.floor(Math.random() * 6) + 1
}

export default function App() {
  const [diceRolls, setDiceRolls] = useState([1, 2, 3])

  return (
    <div>
      <button
        onClick={() => {
          setDiceRolls([...diceRolls, randomDiceRoll()])
        }}
      >
        Roll dice
      </button>
      <ul>
        {diceRolls.map((diceRoll, index) => (
          <li key={index}>{diceRoll}</li>
        ))}
      </ul>
    </div>
  )
}

render(<App />, document.querySelector('#app'))

react usestate

const [count, setCount] = React.useState(0);
  const [count2, setCount2] = React.useState(0);

  // increments count by 1 when first button clicked
  function handleClick(){
    setCount(count + 1);
  } 

  // increments count2 by 1 when second button clicked
  function handleClick2(){
    setCount2(count2 + 1);
  } 

  return (
    <div>
      <h2>A React counter made with the useState Hook!</h2>
      <p>You clicked {count} times</p>
      <p>You clicked {count2} times</p>
      <button onClick={handleClick}>
        Click me
      </button> 
      <button onClick={handleClick2}>
        Click me2
      </button>
  );

useState

1:  import React, { useState } from 'react';
 2:
 3:  function Example() {
 4:    const [count, setCount] = useState(0);
 5:
 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:  }

usestate react

import React, { useState } from 'react';

function Example() {
	
  const [count, setCount] = useState(0);
  
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

usestate

import React, { useState } from 'react';

function Example() {
  	// 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>
    );
}

usestate in react js

import React, { useState } from "react";

const Counter = () => {
  // Here we use the useState -->
  const [count, setCount] = useState(0);

  // Here we make the function of the Count with setCount
  const onClick = () => {
    setCount(count + 1);
  };

  return (
    <div>
        <p>You Clicked {count} On The Button</p>
        <button onClick={onClick}>Click Me></button>
    </div>
  );
};

export default Counter;

react usestate

// Initialize useState.
const [stateVar, setStateVar] = useState();

// The useState parameters define the default value of stateVar.
useState(); // stateVar === undefined
useState(true); // stateVar === true
useState('Hamburger'); // stateVar === 'Hamburger'

// setStateVar is a function that sets the value of stateVar.
setStateVar(value);

// stateVar is equal to the value that was set in the setStateVar-function.
stateVar

/* 
Example usage - Everytime you run toggleActive, the isActive
variable will toggle between false and true.
*/
const [isActive, setIsActive] = useState(false);

function toggleActive() {
	setIsActive(!isActive);
}

react hook usestate

function Counter({initialCount}) {
  const [count, setCount] = useState(initialCount);
  return (
    <>
      Count: {count}
      <button onClick={() => setCount(initialCount)}>Reset</button>
      <button onClick={() => setCount(prevCount => prevCount - 1)}>-</button>
      <button onClick={() => setCount(prevCount => prevCount + 1)}>+</button>
    </>
  );
}

usestate

function ExampleWithManyStates() {
  const [age, setAge] = useState(42);
  const [fruit, setFruit] = useState('banana');
  const [todos, setTodos] = useState([{ text: 'Learn Hooks' }]);

react js usestate

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

import React, { useState } from 'react';

function Example() {
  // 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>
  );
}

React useState Hook

import { useState } from "react"

useState

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

usestate in react

  const [x, setx] = useState(0);

usestate

import React, { useState } from 'react';

function Example() {
  // 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>
  );
}

usestate in react

function handleOrangeClick() {
    // Similar to this.setState({ fruit: 'orange' })
    setFruit('orange');
  }

How to use React useState Hook

useState - Has the main purpose to change an element status
useState basically helps React to know what to elements need to be rerendered. 

Ex: We have a post                 (state: it is displayed) 
    You want to eliminate the post (setState: it is not displayed)

Code Ex.:
const [blogs, setBlogs] = useState([  
    { title: 'React forever', body:'Lorem ipsum...', author: 'Sara', id: 1 },
    { title: 'Vue kinda sucks', body:'Lorem ipsum...', author: 'Tony', id: 2 },
    { title: 'Angular lets not go there', body:'Lorem ipsum...', author: 'John', id: 3 },
  	]);

// The JS function that filters all the post with diff. id from the id of the post clicked
const handleDelete = (id) => {
  const newBlogs = blogs.filter(blog => blog.id !== id);
    setBlogs(newBlogs);
  }

// React renders the following JSX
return (
    <div className="blog-list">
      <h2>{ title }</h2>
        {blogs.map((blog) => (
          <div className="blog-preview" key={blog.id}>
            <h3>{ blog.title }</h3>
            <p>written by { blog.author }</p>
            <p>{ blog.body }</p> 
            <button onClick={() => handleDelete(blog.id)} className="hideBtn">Hide Post</button>
          </div>
        ))}
    </div>
    );
  

usestate in react

The initial value will be assigned only on the initial render (if it’s a function, it will be executed only on the initial render).