Real-Time React Analog Clock

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Introduction

React can be used directly in HTML, even though JSX does not seem to be supported.

In this blog post, I would like to quickly show how to use React to request time and render time as an analog SVG figure for different time zones.

World Time

The local time, Los Angeles time, New York time, Beijing time, London time, and Tokyo time are displayed in real-time.

React-HTML Implementation

This React-HTML implementation does not use JSX, i.e., all the React components were created using React.createElement. It requests UTC time from worldtimeapi.org once every one second and falls back to local time if the request failed. The UTC time will be converted to the local time in different time zones and the local time will be rendered as a SVG figure.

react_analog_clock.html
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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Hello HTML-React Analog Clock!</title>
  </head>
  <body>
    <div id="root"></div>

    <script src="https://unpkg.com/react@18/umd/react.development.js"></script>
    <script src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>
    <script>
      // Create a React component called Clock that displays the current time in a SVG analog clock.
      // The analog clock should have three hands: hour, minute, and second.
      // The analog clock should also have 1, 2, 3, ..., 12 numbers around the clock face.
      // The analog clock should also have tick marks.
      function Clock({ time }) {
        const hour = time.getHours();
        const minute = time.getMinutes();
        const second = time.getSeconds();

        const hourAngle = (hour % 12) * 30 + minute * 0.5;
        const minuteAngle = minute * 6;
        const secondAngle = second * 6;

        const hourHand = React.createElement("line", {
          x1: "50",
          y1: "50",
          x2: "50",
          y2: "20",
          style: {
            transform: `rotate(${hourAngle}deg)`,
            transformOrigin: "center",
            stroke: "black",
            strokeWidth: "3",
          },
        });

        const minuteHand = React.createElement("line", {
          x1: "50",
          y1: "50",
          x2: "50",
          y2: "10",
          style: {
            transform: `rotate(${minuteAngle}deg)`,
            transformOrigin: "center",
            stroke: "black",
            strokeWidth: "2",
          },
        });

        const secondHand = React.createElement("line", {
          x1: "50",
          y1: "50",
          x2: "50",
          y2: "10",
          style: {
            transform: `rotate(${secondAngle}deg)`,
            transformOrigin: "center",
            stroke: "red",
            strokeWidth: "1",
          },
        });

        const clockFace = React.createElement("circle", {
          cx: "50",
          cy: "50",
          r: "40",
          style: {
            fill: "white",
            stroke: "black",
            strokeWidth: "2",
          },
        });

        const clockNumbers = [];
        for (let i = 1; i <= 12; i++) {
          const angle = i * 30;
          const x = 50 + 35 * Math.sin((angle * Math.PI) / 180);
          const y = 50 - 35 * Math.cos((angle * Math.PI) / 180);
          clockNumbers.push(
            React.createElement(
              "text",
              {
                key: `number-${i}`,
                x: x,
                y: y,
                style: {
                  textAnchor: "middle",
                  dominantBaseline: "central",
                  fontSize: "8px",
                },
              },
              `${i}`
            )
          );
        }

        const clock = React.createElement(
          "svg",
          {
            width: "250",
            height: "250",
            viewBox: "0 0 100 100",
            style: {
              // border: "1px solid black",
            },
          },
          clockFace,
          clockNumbers,
          hourHand,
          minuteHand,
          secondHand
        );

        // Wrap the clock in a div element and center it.
        return React.createElement(
          "div",
          {
            style: {
              display: "flex",
              justifyContent: "center",
              alignItems: "center",
            },
          },
          clock
        );
      }

      function App() {
        const [datetime, setDateTime] = React.useState(new Date());

        const cityTimeZones = [
          { name: "Los Angeles", timezone: "America/Los_Angeles" },
          { name: "New York", timezone: "America/New_York" },
          { name: "Beijing", timezone: "Asia/Shanghai" },
          { name: "London", timezone: "Europe/London" },
          { name: "Tokyo", timezone: "Asia/Tokyo" },
          // Add more cities and timezones as needed
        ];

        function getTime(date, timeZone) {
          const time = date.toLocaleTimeString("en-US", {
            timeZone: timeZone,
            year: "numeric",
            month: "2-digit",
            day: "2-digit",
            hour: "2-digit",
            minute: "2-digit",
            second: "2-digit",
            hour12: false,
          });
          return time;
        }

        async function fetchTime() {
          try {
            // Fetch the current time from worldtimeapi.org.
            const response = await fetch("https://worldtimeapi.org/api/ip");
            const data = await response.json();
            const utc_datetime = new Date(data.utc_datetime);
            setDateTime(utc_datetime);
          } catch (error) {
            // Get local datetime if worldtimeapi.org is down.
            setDateTime(new Date());
            console.log(error);
          }
        }

        // Asynchronously update the time roughly every 1000 ms.
        React.useEffect(function () {
          const intervalId = setInterval(function () {
            fetchTime();
          }, 1000);
          return () => clearInterval(intervalId);
        }, []);

        const timeComponents = cityTimeZones.map(
          ({ name, timezone }, index) => {
            const localTime = getTime(datetime, timezone);
            const localDateTime = new Date(localTime);
            return React.createElement(
              "div",
              { key: `zone-${index}` },
              React.createElement("h3", null, `${name}: ${localTime}`),
              React.createElement(Clock, { time: localDateTime }),
              React.createElement("p", null, "")
            );
          }
        );

        return React.createElement(
          "div",
          null,
          React.createElement(
            "h3",
            null,
            `Local: ${getTime(
              datetime,
              Intl.DateTimeFormat().resolvedOptions().timeZone
            )}`
          ),
          React.createElement(Clock, { time: datetime }),
          React.createElement("p", null, ""),
          React.createElement("div", null, timeComponents)
        );
      }
      const root = ReactDOM.createRoot(document.getElementById("root"));
      root.render(React.createElement(App));
    </script>
  </body>
</html>

Real-Time React Analog Clock

https://leimao.github.io/blog/Real-Time-React-Analog-Clock/

Author

Lei Mao

Posted on

09-11-2023

Updated on

10-09-2023

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