useState --simple example

//FavColor.jsx

import React,{useState} from 'react';

const fav=()=>{

const[color,setColor]=useState("red");
  
  return(
<>
    <h1>fav color is {color}</h1>
    <button     type="button"  onClick={()=>setColor("blue")} className="btn1">
    Blue
    </button>

<button type="button"  onClick={()=>setColor("red")}  className="btn2">Red</button>



    </>
  )
}

export default fav;


//App.jsx
import React from 'react';
import FavColor from './FavColor';

export function App() {
  return (
    <div className='App'>
    <FavColor  />

    </div>
  );
}

// use Fetch hook file
import { useState, useEffect } from "react";


const useFetchCities = (url) => { // need this url placeholder to put into where the fetch hook is being called


 const [cities, setCities] = useState([]);
 const [loading, setLoading] = useState(false);
 const [error, setError] = useState(null);



//fetch for local url => move later to a hook
 useEffect(() => {
      const citiesData = async(url) => {
        setLoading(true)
        try {
          const response = await fetch(url);
          if(!response.ok) return
          
          if(response.status === 200){
            const data = await response.json();
            setCities(data)
            
          }
        
        } catch (error) {
          setError(error)
          setLoading(true)
        }finally{
          setLoading(false)
        }
      }
      citiesData(url)
 
 }, [url]);


 return {cities, loading, error}
}


export default useFetchCities;






//import the hook into another file

// fetch hook for cities => see useFetchCties file
const {cities, loading, error} = useFetchCities(`${BASE_URL}/cities`);

// removes all duplicates of a key in a json array, in this case we create a new const that loops over a cities json array and checks for countries with the same name. it will return only the first instance of that country object where there are multiple of the same country

const countriesUnique = new Set(
  cities.map(city =>
    JSON.stringify({ country: city.country, emoji: city.emoji }),
  ),
)
const countries = [...countriesUnique].map(each => JSON.parse(each))
console.log(countries)

import { createContext } from "react";
import useFetch from '../hooks/useFetch' // import the useFetch hook


const BASE_URL = 'http://localhost:8000';


const CitiesContext = createContext();



function CitiesProvider({children}){

    // fetch hook for cities => see useFetchCties file
    const {data: cities, loading, error} = useFetch(`${BASE_URL}/cities`);  


    return(
      <CitiesContext.Provider value={{
          cities: cities,
          loading: loading,
          error: error
      }}>

        {children}
      </CitiesContext.Provider>
    )
}

export {CitiesContext, CitiesProvider}

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

function App() {
  const [age, setAge] = useState(0);
  
  updateAge(value) {
    setDisplayUsaStudents(
            (prevDisplayUsaStudents) => !prevDisplayUsaStudents
          );
    setAge({prevAge: value});
  };

  useEffect(() => {
    if (age !== 0 && age >= 21) {
      // Make API call to /beer
    } else {
      // Throw error 404, beer not found
    }
//the square parentheses with the age state variable inside is called the dependency array. //it tells the useEffect function to listen for any changes to the state of age.
//when age changes, useEffect executes
  }, [age]);

  return (
    <div>
      <p>Drinking Age Checker</p>
      <input
        type="number"
        value={age} 
        onChange={e => setAge(e.target.value)}
      />
    </div>
  );
}

export default App;

//app.js
import React, { useState } from 'react';
import './App.css';

function App() {
  const [firstDieResult, setFirstDieResult] = useState(1);
  const [secondDieResult, setSecondDieResult] = useState(6);
  //OR
  //const [diceResult, setDiceResult] = useState({
  	//firstDieResult: 1,
  	//secondDieResult: 6,
	//});

  const firstDieImage = require(`./assets/${firstDieResult}.png`);
  const secondDieImage = require(`./assets/${secondDieResult}.png`);

  function rollDice() {
    setFirstDieResult(Math.floor(Math.random() * 6) + 1);
    setSecondDieResult(Math.floor(Math.random() * 6) + 1);
  }

  return (
    <div className="App">
      <header className="App-header">
        <div style={{ display: 'flex', margin: 20 }}>
          <img src={firstDieImage} className="die" alt="Die one" />
          <img src={secondDieImage} className="die" alt="Die two" />
        </div>
        <span>{firstDieResult + secondDieResult}</span>
        <button className="button" onClick={rollDice}>Roll</button>
      </header>
    </div>
  );
}

export default App;

//css

.App {
  text-align: center;
}

.App-header {
  background-color: #282c34;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: calc(16px + 2vmin);
  color: white;
}

.die {
  width: 50px;
  height: 50px;
  margin: 10px;
}

.button {
  margin-top: 20px;
  outline: none;
  animation: button-gradient 25s ease infinite;
  background-image: -webkit-linear-gradient(65deg,#21d4fd,#b721ff 50%,#017eff);
  background-image: linear-gradient(25deg,#21d4fd,#b721ff 50%,#017eff);
  background-size: 500%;
  border: none;
  border-radius: 3px;
  box-shadow: 0 3px 0 0 #5664a7;
  color: #fff;
  font-size: 14px;
  font-weight: 600;
  height: 40px;
  width: 150px;
}

.button:hover {
  box-shadow: 0 2px 0 0 #5664a7;
}

.button:active {
  box-shadow: inset 0 2px 4px rgba(0,0,0,0.25), 0 1px 2px rgba(0,0,0,0.05);
}
// get images => https://upmostly.com/wp-content/uploads/react-dice-assets.zip

import React, { useState } from 'react'

const MyComponent = () => {
  const [toggle, setToggle] = useState(false)

  return(
    <>
      <button onClick={() => setToggle(!toggle)}>Toggle Dropdown Markup</button>
      {toggle && (
        <ul>
          <li>Show me</li>
          <li>Only when</li>
          <li>Toggle === true</li>
        </ul>
      )}
    </>
  )
}

import React, { useState } from "react";
import "./App.css";

const App = () => {
  const [counterA, setCounterA] = useState(0);
  const [counterB, setCounterB] = useState(0);

  return (
    <div>
      <button
        onClick={() => {
          setCounterA(counterA + 1);
        }}
      >
        Increment A
      </button>
      <button
        onClick={() => {
          setCounterB(counterB + 1);
        }}
      >
        Increment B
      </button>
      <div>counterA: {counterA}</div>
      <div>counterB: {counterB}</div>
    </div>
  );
};

export default App;

import { useState } from "react";
import ReactDOM from "react-dom/client";

function Car() {
  const [car, setCar] = useState({
    brand: "Ford",
    model: "Mustang",
    year: "1964",
    color: "red"
  });

  const updateColor = () => {
    setCar(previousState => {
      return { ...previousState, color: "blue" }
    });
  }

  return (
    <>
      <h1>My {car.brand}</h1>
      <p>
        It is a {car.color} {car.model} from {car.year}.
      </p>
      <button
        type="button"
        onClick={updateColor}
      >Blue</button>
    </>
  )
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<Car />);