How to clear a previous interval with React-CodePudding

I'm working on a simple game using React and came across a problem. So whenever you press W A S or D, an interval starts. What I want is whenever the user presses a key, the previous interval is cleared before starting the next one so that only one interval is executing at a time.

import { useState } from "react"

export default function useGame() {
  const [xpos, setXpos] = useState(250)
  const [ypos, setYpos] = useState(250)

  const handleKeypress = (e) => {
    if (e.key === "w") {
      setInterval(() => {
        setYpos((prev) => {
          return (prev -= 5)
        })
      }, 100)
    }
    if (e.key === "s") {
      setInterval(() => {
        setYpos((prev) => {
          return (prev  = 5)
        })
      }, 100)
    }
    if (e.key === "a") {
      setInterval(() => {
        setXpos((prev) => {
          return (prev -= 5)
        })
      }, 100)
    }
    if (e.key === "d") {
      setInterval(() => {
        setXpos((prev) => {
          return (prev  = 5)
        })
      }, 100)
    }
  }

  return { handleKeypress, xpos, ypos }
}

I've tried storing the interval ID in state but its always undefined in other functions or other parts of the code. How would you guys go about solving this?

CodePudding user response：

You need to store interval id returned by setInterval and pass it to clearInterval whenever you want to clear that interval.

function App() {

        const [count, setCount] = useState(0);
        const [intervalId, setIntervalId] = useState(null);

        const startCounting = () => {
            const id = setInterval(()=>{
                setCount(prevCount => prevCount   1);
            }, 1000);
            setIntervalId(id);
        }

        return (<div>
            <div>{count}</div>
            <button onClick={startCounting}>Start Interval</button>
            <button onClick={()=>clearInterval(intervalId)}>Stop Interval</button>
        </div>);

}

In you question you have created separate interval depending on each condition, and every interval will have different interval id. so better put all condition into single setInterval and return its interval id.

import { useState } from "react"

export default function useGame() {
    const [xpos, setXpos] = useState(250)
    const [ypos, setYpos] = useState(250)
    const [intervalId, setIntervalId] = useState(null);

    const handleKeypress = (e) => {
        const id = setInterval(() => {
            if (e.key === "w") {
                setYpos((prev) => {
                    return (prev -= 5)
                })
            }
            if (e.key === "s") {
                setYpos((prev) => {
                    return (prev  = 5)
                })
            }
            if (e.key === "a") {
                setXpos((prev) => {
                    return (prev -= 5)
                })
            }
            if (e.key === "d") {
                setXpos((prev) => {
                    return (prev  = 5)
                })
            }
        }, 100);
        setIntervalId(id);
    }

    return { handleKeypress, xpos, ypos, intervalId }
}

CodePudding user response：

import { useState } from "react"

export default function useGame() {
  const [intervalId, setIntervalId] = useState(Number(0));
  const [xpos, setXpos] = useState(250)
  const [ypos, setYpos] = useState(250)

  const handleKeypress = (e) => {
    if (e.key === "w") {
      if(intervalId > 0) {
        clearInterval(intervalId);
      }
      let id = setInterval(() => {
        setYpos((prev) => {
          return (prev -= 5)
        })
      }, 100)
      setIntervalId(Number(id));
    }
    if (e.key === "s") {
      if(intervalId > 0) {
        clearInterval(intervalId);
      }
      let id = setInterval(() => {
        setYpos((prev) => {
          return (prev  = 5)
        })
      }, 100)
      setIntervalId(Number(id))
    }
    if (e.key === "a") {
      if(intervalId > 0) {
        clearInterval(intervalId);
      }
      let id = setInterval(() => {
        setXpos((prev) => {
          return (prev -= 5)
        })
      }, 100)
      setIntervalId(Number(id))
    }
    if (e.key === "d") {
      if(intervalId > 0) {
        clearInterval(intervalId);
      }
      let id =setInterval(() => {
        setXpos((prev) => {
          return (prev  = 5)
        })
      }, 100)
      setIntervalId(Number(id))
    }
  }

  return { handleKeypress, xpos, ypos }
}

clearInterval