Шпаргалка по React

// example Context object
const ThemeContext = React.createContext("dark");

// usage with context Consumer
function Button() {
  return <ThemeContext.Consumer>
        {theme => <button className={theme}> Amazing button </button>}
  </ThemeContext.Consumer>
}


// usage with useContext hook 
import {useContext} from 'react';

function ButtonHooks() {
 const theme = useContext(ThemeContext)
 return <button className={theme}>Amazing button</button>
}

const ThemeContext = React.createContext('light');

const Display = () => {
 const theme = useContext(ThemeContext);
 return <div
        style={{
        background: theme === 'dark' ? 'black' : 'papayawhip',
        color: theme === 'dark' ? 'white' : 'palevioletred',
        width: '100%',
        minHeight: '200px'
        }}
    >
        {'The theme here is ' + theme}
    </div>
}

function App() {
  const [player, setPlayer] = React.useState("");
  const [players, setPlayers] = React.useState(["Messi", "Ronaldo", "Laspada"]);

  function handleChangeInput(event) {
    setPlayer(event.target.value);
  }
  function handleAddPlayer() {
    setPlayers(players.concat(player));
  }
  const handleRemovePlayer = useCallback(player => {
    setPlayers(players.filter((p) => p !== player));
  }, [players])

  return (
    <>
      <input onChange={handleChangeInput} />
      <button onClick={handleAddPlayer}>Add Player</button>
      <PlayerList players={players} handleRemovePlayer={handleRemovePlayer} />
    </>
  );
}

function PlayerList({ players, handleRemovePlayer }) {
  return (
    <ul>
      {players.map((player) => (
        <li key={player} onClick={() => handleRemovePlayer(player)}>
          {player}
        </li>
      ))}
    </ul>
  );
}

function App() {
    const [count, setCount] = useState(10)

    const expensiveComputation = useMemo(() => {
        return count * 2
    }, [count])

    return (
        <>
            <p>Count: {count}</p>
            <p>Expensive count: {expensiveComputation}</p>
            <button onClick={() => setCount(count + 1)}>Increment count</button>
        </>
    )
}

import * as React from 'react'
import {getMDXComponent} from 'mdx-bundler/client'

function Post({code, frontmatter}) {
  const Component = React.useMemo(() => getMDXComponent(code), [code]);

  return (
    <>
      <header>
        <h1>{frontmatter.title}</h1>
        <p>{frontmatter.description}</p>
      </header>
      <main>
        <Component />
      </main>
    </>
  )
}

const App = () => {
    const [age, setAge] = useState(99)
    const handleClick = () => setAge(age + 1)
    const someValue = useMemo(() => ({ value: "someValue" }))
    const doSomething = () => {
      return someValue
    }

    return (
      <div>
        <Age age={age} handleClick={handleClick}/>
        <Instructions doSomething={doSomething} />
      </div>
    )
}

const Age = ({ age, handleClick }) => {
  return (
    <div>
      <div style={{ border: '2px', background: "papayawhip", padding: "1rem" }}>
        Today I am {age} Years of Age
      </div>
      <pre> - click the button below 👇 </pre>
      <button onClick={handleClick}>Get older! </button>
    </div>
  )
}

const Instructions = React.memo((props) => {
  return (
    <div style={{ background: 'black', color: 'yellow', padding: "1rem" }}>
      <p>Follow the instructions above as closely as possible</p>
    </div>
  )
})

ReactDOM.render (<App />)

function App() {

    function reducer(state, action) {
        switch (action.type) {
            case 'plus':
                return state + 1
            case 'minus':
                return state - 1
        }
    }

    const [count, dispatch] = useReducer(reducer, 0)

    return (
        <>
            Count: {count}
            <button onClick={() => dispatch({ type: 'plus' })}>Plus 1</button>
            <button onClick={() => dispatch({ type: 'minus' })}>Minus 1</button>
        </>
    )
}

const ArrayDep = () => {
    const [randomNumber, setRandomNumber] = useState(0)
    const [effectLogs, setEffectLogs] = useState([])

    useLayoutEffect(
      () => {
        setEffectLogs(prevEffectLogs => [...prevEffectLogs, 'effect fn has been invoked'])
      },
      [randomNumber]
    )

    return (
      <div>
        <h1>{randomNumber}</h1>
        <button
          onClick={() => {
            setRandomNumber(Math.random())
          }}
        >
          Generate random number!
        </button>
        <div>
          {effectLogs.map((effect, index) => (
            <div key={index}>{'🍔'.repeat(index) + effect}</div>
          ))}
        </div>
      </div>
    )
  }

const initialState = { width: 15 };

const reducer = (state, action) => {
  switch (action) {
    case 'plus':
      return { width: state.width + 15 }
    case 'minus':
      return { width: Math.max(state.width - 15, 2) }
    default:
      throw new Error("what's going on?" )
  }
}

const Bar = () => {
  const [state, dispatch] = useReducer(reducer, initialState)
  return <>
    <div style={{ background: 'teal', height: '30px', width: state.width }}></div>
    <div style={{marginTop: '3rem'}}>
        <button onClick={() => dispatch('plus')}>Increase bar size</button>
        <button onClick={() => dispatch('minus')}>Decrease bar size</button>
    </div>
    </>
}

ReactDOM.render(<Bar />)

const initializeState = () => ({
  width: 100
})


const initialState = { width: 15 }
const reducer = (state, action) => {
  switch (action) {
    case 'plus':
      return { width: state.width + 15 }
    case 'minus':
      return { width: Math.max(state.width - 15, 2) }
    default:
      throw new Error("what's going on?" )
  }
}

const Bar = () => {
  const [state, dispatch] = useReducer(reducer, initialState, initializeState)
  return <>
    <div style={{ background: 'teal', height: '30px', width: state.width }}></div>
    <div style={{marginTop: '3rem'}}>
        <button onClick={() => dispatch('plus')}>Increase bar size</button>
        <button onClick={() => dispatch('minus')}>Decrease bar size</button>
    </div>
    </>
}

ReactDOM.render(Bar)

function Form() {
  function handleSubmit(e) {
    e.preventDefault();
    console.log('You clicked submit.');
  }

  return (
    <form onSubmit={handleSubmit}>
      <button type="submit">Submit</button>
    </form>
  );
}

import React, { Suspense } from 'react';

const OtherComponent = React.lazy(() => import('./OtherComponent'));

function MyComponent() {
  return (
    <div>
       //fallback prop’u, bileşenin 
       yüklenmesini beklerken göstermek 
       istediğiniz herhangi bir React elemanını 
       kabul eder. 
      <Suspense fallback={<div>Yükleniyor...</div>}>
        <OtherComponent />
      </Suspense>
    </div>
  );
}

const [isPending, startTransition] = useTransition();

startTransition(() => {
  setCount(count + 1);
})

function App() {
  const [isPending, startTransition] = useTransition();
  const [count, setCount] = useState(0);

  function handleClick() {
    startTransition(() => {
      setCount(c => c + 1);
    })
  }

  return (
    <div>
      {isPending && <Spinner />}
      <button onClick={handleClick}>{count}</button>
    </div>
  );
}

const Person = ({name, age, children}) => {
    return (
        <h1>Name: {name} Age: {age}</h1>
        <p>{children}</p>
    )
}

Person.defaultProps = {
    name: 'No name',
    age: 0,
}

function App(){
  return people.map(person => <Person key={person.id} {...person} />)
}

const Person = ({name, age}) => {
  return (
      <h1>Name: {name}, Age: {age}</h1>
  )
}