I'm trying to make a simple setInterval function for a typing game but it keeps glitching out depending on my syntax or not updating at all as it is now.

How do I get this to update every second and call the functions in the if statement?

const [counter, setCounter] = useState(10);

useEffect(() => {
  let timer = setInterval(() => {
    setCounter(counter - 1);

    if (counter === 0) {
      setWordIndex(wordIndex + 1);
      setLives(lives - 1);
      life.play();
      setCounter(10);
    }
  }, 1000);
}, []);

*********Edit***************

This is what I have now that is working. The first answer fixed the async issue of the counter not decrementing but I had to move the if statement outside of the useEffect to correct what I believe was caused by this same problem.

 useEffect(() => {
    let timer = setInterval(() => {
      setCounter( counter => counter - 1);
    }, 1000);
  }, []);
  if (counter == 0) {
    setWordIndex(wordIndex + 1);
    setLives(lives - 1);
    life.play();
    setCounter(10);
  }

I'm trying to make a simple setInterval function for a typing game but it keeps glitching out depending on my syntax or not updating at all as it is now.

How do I get this to update every second and call the functions in the if statement?

const [counter, setCounter] = useState(10);

useEffect(() => {
  let timer = setInterval(() => {
    setCounter(counter - 1);

    if (counter === 0) {
      setWordIndex(wordIndex + 1);
      setLives(lives - 1);
      life.play();
      setCounter(10);
    }
  }, 1000);
}, []);

*********Edit***************

This is what I have now that is working. The first answer fixed the async issue of the counter not decrementing but I had to move the if statement outside of the useEffect to correct what I believe was caused by this same problem.

 useEffect(() => {
    let timer = setInterval(() => {
      setCounter( counter => counter - 1);
    }, 1000);
  }, []);
  if (counter == 0) {
    setWordIndex(wordIndex + 1);
    setLives(lives - 1);
    life.play();
    setCounter(10);
  }

• javascript
• reactjs
• settimeout
• setinterval
• use-effect

• Remember to reconsult the useState docs every now and then. – Mike 'Pomax' Kamermans Commented Jan 7, 2020 at 3:24
• Does this answer your question? setInterval in a React app – Emile Bergeron Commented Jan 7, 2020 at 3:28

3 Answers 3

Use callback function in setCounter function. As you are calling the state update in an async function. it's good practice to update the state based on the previous state.

const [counter, setCounter] = useState(10);
useEffect(() => {
    let timer = setInterval(() => {
        setCounter(counter => {
            const updatedCounter = counter - 1;
            if (updatedCounter === 0) {
                setWordIndex(wordIndex + 1);
                setLives(lives - 1);
                life.play();
                return 10;
            }
            return updatedCounter;
        }); // use callback function to set the state

    }, 1000);
    return () => clearInterval(timer); // cleanup the timer
}, []);

The previous answers aren't considering the counter values aren't immediately updating. They are also prone memory leaks since setInterval isn't cleared.

const [counter, setCounter] = useState(10);
useEffect(() => {
  let timer = setInterval(() => {
    setCounter( counter => {
        const nC = counter - 1;
        if (nC === 0) {
           setWordIndex(wordIndex + 1);
           setLives(lives - 1);
           life.play();
           return 10;
        }
        return nC;
     });
  }, 1000);
  return () => clearInterval(timer);
}, []);

The previous answers weren't considering other states - wordIndex and lives and didn't include clear Intervals

It's advisable to use callback setState inside setIntervals and clear the interval on next useEffect call

  const [counter, setCounter] = React.useState(10);
  React.useEffect(() => {
    let timer = setInterval(() => {
      // It's advisable to use callback setState inside setIntervals
      setCounter(prev => {
        if (prev !== 0) return prev - 1;

        setWordIndex(wordIndex + 1);
        setLives(lives - 1);
        life.play();    
        return 10;
      });
    }, 1000);

    // And clear the interval next useEffect call
    return () => clearInterval(timer);
  }, [wordIndex, lives]);