I looked through a lot of resources for building a clock using React Hooks but all I found was the one using React class components, so here's one using React Hooks!

P.S. you can go to the bottom of the blog for live codepen embed where you can play around with the code!

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Step 1: Create a functional component 'Clock'.

const Clock = () => {
    //empty for now
}

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Step 2: use "new Date()" to get the current time.

const Clock = () => {
    return (
        <div className="container">
            <h1>
                {new Date().toLocaleTimeString()} (IST)
            </h1>    
        </div>
    )
}

Here the "new Date().toLocaleTimeString()" returns the current time in format "hh-mm-ss" but notice that it doesn't re-render, and we'll do that using useState and useEffect methods!

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Step 3: Store the current time in useState.

const Clock = () => {

    const [timer, setTimer] = useState(new Date())

    return (
        <div className="container">
            <h1>
                {new Date().toLocaleTimeString()} (IST)
            </h1>    
        </div>
    )
}

we will initialize the state with "new Date()" and update it in the next step.

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Step 4: Create a function tick and call it every second using useEffect!

Create a tick function that set's the timer to new Date whenever it is called, so the useEffect makes use of setInterval to render it every 1000ms or 1s. Atlast make sure you change the "new Date()" to "timer" of the state.

const Clock = () => {

    const [timer, setTimer] = useState(new Date())

    function tick() {
        setTimer(new Date)
    }

    React.useEffect(() => {
        let timerID = setInterval(() => {
            tick()
        }, 1000)

        return () => {
            clearInterval(timerID)
        }
    })

    return (
        <div className="container">
            <h1>
                {timer.toLocaleTimeString()} (IST)
            </h1>    
        </div>
    )
}

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Live playground for you to play with the code👇

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