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August 17, 2020 19:19
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Counters example using reducer
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="UTF-8" /> | |
| <title>Clock</title> | |
| <!-- don't use this in production: --> | |
| <script src="https://unpkg.com/@babel/standalone/babel.min.js"></script> | |
| </head> | |
| <body> | |
| <h1 style="font-family: Arial;">counters</h1> | |
| <!-- target div --> | |
| <div id="root"></div> | |
| <!-- load react --> | |
| <script | |
| src="https://unpkg.com/react/umd/react.development.js" | |
| crossorigin | |
| ></script> | |
| <script | |
| src="https://unpkg.com/react-dom/umd/react-dom.development.js" | |
| crossorigin | |
| ></script> | |
| <!-- react component. --> | |
| <script src="reducer.js" defer type="text/babel"></script> | |
| </body> | |
| </html> |
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| const Counter = (props) => { | |
| const [counter, setCounter] = React.useState(Number(props.start)); | |
| // useRef to avoid the closure in the timer | |
| const countRef = React.useRef(counter); | |
| countRef.current = counter; | |
| // timer | |
| React.useEffect(() => { | |
| const timeout = setTimeout(() => { | |
| setCounter(counter + Number(props.increment)); | |
| props.parent({label: props.label, value: countRef.current}); | |
| }, props.interval); | |
| // cleanup | |
| return () => { | |
| clearTimeout(timeout); | |
| } | |
| }, [counter]); | |
| return ( | |
| <> | |
| Child-{props.label}: {counter} | |
| </> | |
| ); | |
| } | |
| function reducer(state, action) { | |
| switch (action.type) { | |
| case '01': | |
| return {...state, counter01: action.value}; | |
| case '02': | |
| return {...state, counter02: action.value}; | |
| case '03': | |
| return {...state, counter03: action.value}; | |
| default: | |
| throw new Error(); | |
| } | |
| } | |
| let initialState = {counter01: 0, counter02: 0, counter03: 0}; | |
| const Stats = () =>{ | |
| const [state, dispatch] = React.useReducer(reducer, initialState); | |
| function parent(counter){ | |
| dispatch({type:counter.label, value: counter.value}) | |
| } | |
| return ( | |
| <div> | |
| <Counter | |
| style={{padding:'25px 50px 75px 100px;'}} | |
| label="01" | |
| start="0" | |
| increment="2" | |
| interval="1000" | |
| parent={parent} />,<br/> | |
| Parent01: {state.counter01} <br/> | |
| <Counter | |
| label="02" | |
| start="0" | |
| increment="10" | |
| interval="2000" | |
| parent={parent} />,<br/> | |
| Parent02: {state.counter02} <br/> | |
| <Counter | |
| label="03" | |
| start="0" | |
| increment="5" | |
| interval="3000" | |
| parent={parent} /><br/> | |
| Parent03: {state.counter03} <br/> | |
| </div> | |
| ) | |
| } | |
| ReactDOM.render( | |
| <Stats />, | |
| document.getElementById('root') | |
| ); |
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