Created
December 3, 2021 18:25
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React demo
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import React, { useState, useEffect, useReducer, useMemo } from 'react' | |
import ReactDOM from 'react-dom' | |
// let text = 'hellllooooo' | |
// I AM REACT | |
// let domTable = {} | |
// let element = Counter // state = 0 | |
// commit(element, domTable) | |
// let oldElement = element | |
// element = Counter // state = 1 | |
// diff(element, oldElement) | |
// commit(diff) | |
function useDocumentTitle(message) { | |
useEffect(() => { | |
document.title = message | |
}, [message]) | |
} | |
let array = [1, 2, 3, 4, 5] | |
let add = (x, y) => { | |
return x + y | |
} | |
let sum = array.reduce(add, 0) | |
console.log(sum) | |
// 0 + 1 | |
// 1 + 2 | |
// 3 + 3 | |
// 6 + 4 | |
// 10 + 5 | |
// 15 | |
const initialState = { count: 0, cake: true, user: {} } | |
const actions = [ | |
{ type: 'ADD', by: 2 }, | |
{ type: 'MINUS', by: 4 }, | |
{ type: 'EAT_CAKE' }, | |
] | |
function reducer(state, action) { | |
if (action.type === 'ADD') { | |
return { ...state, count: state.count + action.by } | |
} else if (action.type === 'MINUS') { | |
return { ...state, count: state.count - action.by } | |
} else { | |
return { ...state, cake: false } | |
} | |
} | |
console.log(actions.reduce(reducer, initialState)) | |
const Pokemon = () => { | |
// const [pokemon, setPokemon] = useState('pikachu') | |
// const [img, setImg] = useState(null) | |
// const [error, setError] = useState(null) | |
const [state, dispatch] = useReducer( | |
(state, action) => { | |
switch (action.type) { | |
case 'LOAD_POKEMON': { | |
return { ...state, pokemon: action.name, img: action.img } | |
} | |
case 'ERROR': { | |
return { ...state, error: action.error } | |
} | |
case 'USER_INPUT': { | |
return { ...state, pokemon: action.pokemon } | |
} | |
default: { | |
return state | |
} | |
} | |
}, | |
{ | |
pokemon: 'pikachu', | |
img: null, | |
error: null, | |
} | |
) | |
let { pokemon, img, error } = state | |
let someValue = useMemo(() => { | |
// expensive | |
return 'cake' + pokemon | |
}, [pokemon]) | |
let message = 'Go ' + pokemon + '!' | |
useDocumentTitle(message) | |
// [var] // Effect is run on initial render, and when var changes | |
// [] // Effect is run on initial render only | |
// nothing // Run on initial render, AND every state change | |
useEffect(() => { | |
let isCurrent = true | |
fetch(`https://pokeapi.co/api/v2/pokemon/${pokemon}/`) | |
.then((res) => res.json()) | |
.then((res) => { | |
if (isCurrent) { | |
dispatch({ | |
type: 'LOAD_POKEMON', | |
name: res.name, | |
img: res.sprites.front_default, | |
}) | |
// setPokemon(res.name) | |
// setImg(res.sprites.front_default) | |
} | |
}) | |
.catch((emAll) => { | |
// setError(emAll) | |
dispatch({ type: 'ERROR', emAll }) | |
}) | |
return () => { | |
isCurrent = false | |
} | |
}, [pokemon, img, error]) | |
return ( | |
<div> | |
<input | |
onChange={(event) => { | |
// setPokemon(event.target.value) | |
dispatch({ type: 'USER_INPUT', pokemon: event.target.value }) | |
}} | |
value={pokemon} | |
type="text" | |
/> | |
<br /> | |
Hello {pokemon}! | |
<br /> | |
{img && <img src={img} alt={pokemon} />} | |
</div> | |
) | |
} | |
function Counter() { | |
let [count, setCount] = useState(0) | |
let [error, setError] = useState(false) | |
const add = () => { | |
setCount(count + 1) | |
} | |
const subtract = () => { | |
setCount(count - 1) | |
} | |
return ( | |
<div> | |
<div>Current count: {count}</div> | |
<Button fish={add}>Add</Button> | |
<Button fish={subtract}>Subtract</Button> | |
</div> | |
) | |
} | |
const Button = ({ children, fish }) => { | |
return <button onClick={fish}>{children}</button> | |
} | |
const domElement = document.getElementById('root') | |
ReactDOM.render( | |
<div> | |
<Pokemon /> | |
<Counter /> | |
</div>, | |
domElement | |
) |
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