alayek

  import * as React from "react";
  const TICK_INTERVAL: number = 1000;

  function App() {
    const [counter, setCounter] = React.useState<number>(0);
    React.useEffect(() => {
      const startTime = Date.now();
      const timer = setInterval(() => {
        setCounter(_ => {
          const timeNow = Date.now();
          return Math.round((timeNow - startTime) / TICK_INTERVAL);
        });
      }, TICK_INTERVAL);
      return () => {
        if (timer) {
          clearInterval(timer);
        }
      };
    }, []);
    return (
      <div className="App">
        <h1>{counter}</h1>
      </div>
    );

  const TICK_INTERVAL: number = 1000;

  function App() {
    const [counter, setCounter] = React.useState<number>(0);
    const startTime = React.useRef<ReturnType<typeof Date.now>>(Date.now());
    const isVisible: boolean = useVisibility(); // assume taken from NPM
    React.useEffect(() => {
      const timer = setInterval(
        () => {
          if (TICK_INTERVAL && isVisible) {
            setCounter(_ => {
              const timeNow = Date.now();
              return Math.round((timeNow - startTime.current) / TICK_INTERVAL);
            });
          }
        },
        isVisible ? TICK_INTERVAL : null
      );
      return () => {
        if (timer) {
          clearInterval(timer);
        }
      };
    }, [isVisible]);
    return (
      <div className="App">
        <h1>{counter}</h1>
      </div>
    );
  }