React Hook

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

function Example() {
    const [count, setCount] = useState(0);
    useEffect(() => {
        document.title = `You clicked ${count} times`;
    });

    return (
        <div>
            <p>You clicked {count} times</p>
            <button onClick={() => setCount(count + 1)}>
                Clickkk
            </button>
        </div>
    );
}

export default Example

　　

import React, { useState } from 'react'

const LoginControl = (props) => {
    const [flag, setFlag] = useState(false)
    const [cnt, setCnt] = useState(0)
    const changeState = () => {
        setFlag(state => {
            return !state
        })
        setCnt(state => {
            let newCnt = state
            newCnt ++
            return newCnt
        })
    }

    let show = <h1 style={{ color: flag ? "red" : "yellow" }}>i see u</h1>
    let button = <button onClick={changeState}>clickkkk</button>

    return (
        <>
            {show}
            {button}
            <div>
                <button onClick={() => setCnt(cnt + 1)}>numberrr</button>
                <p>{cnt}</p>
            </div>
        </>
    )
}

export default LoginControl

　　

import React, {useState} from 'react';

const SelectVal = (props) => {
    const [val, setVal] = useState("请选择");
    const changeState = (event) => {
        setVal(event.target.value)
    }

    const showVal = (props) => {
        alert(val);
    }
    
    return (
        <>
            <select value={val} onChange={changeState}>
                <option value="请选择">请选择</option>
                <option value="grapefruit">grapfruit</option>
                <option value="lime">lime</option>
                <option value="mango">mango</option>
            </select>
            <button onClick={showVal}>clickkk</button>
        </>
    )
}

export default SelectVal

import React, {useState} from 'react';

const SubmitName = (props) => {
    const[name, setName] = useState("");
    const save = (event) => {
        setName(event.target.value)
    }

    const submittt = (props) => {
        if(!name) alert("请输入姓名");
        else alert(name);
    }

    return (
        <form onSubmit = {submittt}>
        <label>
            输入：
            <input type="text" value={name} onChange={save} />
        </label>
        <input type = "submit" value="提交" />
        </form>
    )

}

export default SubmitName

import React, {useState} from 'react';

const Checkkk = (props) => {
    const [checkk, setCheckk] = useState(false)
    const [cnt, setCnt] = useState(0);

    const sum = () => {
        let count = cnt;
        count ++;
        setCnt(count);
        realy(count);
    }

    const mul = () => {
        let count = cnt;
        count --;
        setCnt(count);
        realy(count);
    }

    const realy = (curCnt) => {
        if(curCnt >= 9) {
            setCheckk(true);
        } else {
            setCheckk(false);
        }
    }

    return (
        <>
        <label style={{color : checkk ? "red" : "yellow"}}>
            ???
            <input type="checkbox" checked={checkk} ></input>
        </label>
        
        <br />
        <input type = "text" value={cnt}/>
        <div>
            <button onClick={sum}>+</button>
            <button onClick={mul}>-</button>
        </div>
        </>
    )

}

export default Checkkk

import React, {useState} from 'react';

const Boil = (props) => {
    const[temp, setTemp] = useState(0);

    const Boiling = (event) => {
        setTemp(event.target.value);
    }

    return (
        <fieldset>
            <legend>Enter</legend>
            <input value={temp} onChange = {Boiling}/>
            <legend>{temp > 100 ? "gulugulu" : "nonono"}</legend>
        </fieldset>
    )
}

export default Boil

import React, {useContext, useReducer} from 'react'

const intial = {
    hello: 'hellooo',
    welcome: 'Zlrrr',
    sel: 'yellow'
}

const Context = React.createContext()

const helloReducer = (state, action) => {
    switch(action.type) {
        case 'translateHello': {
            if(state === 'hellooo') {
                return 'hihihi'
            } else {
                return 'hellooo'
            }
        }
        case 'setHello': {
            return action.value
        }
        default: return state
    }
}

const welcomeReducer = (state, action) => {
    return state
}

const selectReducer = (state, action) => {
    switch(action.type) {
        case 'setSel' : {
            return action.value
        }
        default: return state
    }
}

const reducer = (state ,action) => {
    return {
        hello: helloReducer(state.hello, action),
        welcome: welcomeReducer(state.welcome, action),
        sel: selectReducer(state.sel, action)
    }
}

const HelloInput = (props) => {
    const {reducer} = useContext(Context)
    const dispatch = reducer[1]
    const onChange = (event) => {
        dispatch({
            type: 'setHello',
            value: event.target.value
        })
    }
    return (
        <input onChange={onChange}></input>
    )
}

const HelloText = (props) => {
    const {reducer} = useContext(Context)
    const state = reducer[0]
    return  (
        <>
        <h1>{state.hello + ' ' + state.welcome}</h1>
        </>
    )
}

const HelloButton = (props) => {
    const {reducer} = useContext(Context)
    const dispatch = reducer[1]
    const click = () => {
        dispatch({
            type: 'translateHello'
        })
    }
    return (
        <button onClick = {click}>
            changee
        </button>
    )
}

const HelloSelect = (props) => {
    const {reducer} = useContext(Context)
    const state = reducer[0]
    const dispatch = reducer[1]
    const change = (event) => {
        dispatch({
            type: 'setSel',
            value: event.target.value
        })
    }
    return (
        <select value={state.sel} onChange={change}>
            <option value="red">red</option>
            <option value="orange">orange</option>
            <option value="green">green</option>
            <option value="yellow">yellow</option>
        </select>
    )
}

const App3 = () => {
    const contextValue = {
        reducer: useReducer(reducer, intial)
    }
    return (
        <Context.Provider value={contextValue}>
            <HelloText />
            <HelloInput />
            <HelloButton />
            <br />
            <HelloSelect />
        </Context.Provider>
    )
}

export default App3 

import React, {useContext, useReducer} from 'react'

const intial = {
    hello: 'hellooo',
    welcome: 'Zlrrr',
    sel: 'purple'
}

const Context = React.createContext()

const helloReducer = (state, action) => {
    switch(action.type) {
        case 'translateHello': {
            if(state === 'hellooo') {
                return 'hihihi'
            } else {
                return 'hellooo'
            }
        }
        case 'setHello': {
            return action.value
        }
        default: return state
    }
}

const welcomeReducer = (state, action) => {
    return state
}

const selectReducer = (state, action) => {
    switch(action.type) {
        case 'setSel' : {
            return action.value
        }
        default: return state
    }
}

const reducer = (state ,action) => {
    return {
        hello: helloReducer(state.hello, action),
        welcome: welcomeReducer(state.welcome, action),
        sel: selectReducer(state.sel, action)
    }
}

const HelloInput = (props) => {
    const {reducer} = useContext(Context)
    const dispatch = reducer[1]
    const onChange = (event) => {
        dispatch({
            type: 'setHello',
            value: event.target.value
        })
    }
    return (
        <input onChange={onChange}></input>
    )
}

const HelloText = (props) => {
    const {reducer} = useContext(Context)
    const state = reducer[0]
    return  (
        <>
        <h1 style={{color: state.sel}}>{state.hello + ' ' + state.welcome}</h1>
        </>
    )
}

const HelloButton = (props) => {
    const {reducer} = useContext(Context)
    const dispatch = reducer[1]
    const click = () => {
        dispatch({
            type: 'translateHello'
        })
    }
    return (
        <button onClick = {click} style={{marginLeft: "10px"}}>
            changee
        </button>
    )
}

const HelloSelect = (props) => {
    const {reducer} = useContext(Context)
    const state = reducer[0]
    const dispatch = reducer[1]
    const change = (event) => {
        dispatch({
            type: 'setSel',
            value: event.target.value
        })
    }
    return (
        <div style={{marginTop: "5px"}} >
            <label>
            colorrr
                <select value={state.sel} onChange={change} style = {{marginLeft: "10px"}} >
                    <option value="red">red</option>
                    <option value="orange">orange</option>
                    <option value="yellow">yellow</option>
                    <option value="green">green</option>
                    <option value="blue">blue</option>
                    <option value="purple">purple</option>
                </select>
            </label>
        </div>
    )
}

const App3 = () => {
    const contextValue = {
        reducer: useReducer(reducer, intial)
    }
    return (
        <Context.Provider value={contextValue}>
            <HelloText />
            <HelloInput />
            <HelloButton />
            <br />
            <HelloSelect />
        </Context.Provider>
    )
}

export default App3