Tips on preventing Typescript error TS2531 related to potentially null objects

Question

Tips on preventing Typescript error TS2531 related to potentially null objects

I'm working on retrieving the scroll position using the code snippet below:

    useEffect (()=>{
    document.addEventListener("scroll", e => {
        let scrolled = document.scrollingElement.scrollTop;
        if (scrolled >= 5){
           setPos("moved")
        } else {
           setPos("top")
        }
    })
  },[])

However, Typescript is flagging an issue with the document.scrollingElement.scrollTop property, suggesting that it could possibly be null. How can I address this error and ensure Typescript remains satisfied?

typescript react-native

Answer 1

Answer №1

There are a couple of ways to approach this situation.

Stop the function if the element doesn't exist.

document.addEventListener("scroll", e => {
  if (!document.scrollingElement) {
    return;
  }

  let scrolled = document.scrollingElement.scrollTop;
  ...
});

Utilize the exclamation mark operation for checking:

document.addEventListener("scroll", e => {
  let scrolled = document.scrollingElement!.scrollTop;
  ...
});

Answer 2

There are a couple of ways to approach this situation.

Stop the function if the element doesn't exist.

document.addEventListener("scroll", e => {
  if (!document.scrollingElement) {
    return;
  }

  let scrolled = document.scrollingElement.scrollTop;
  ...
});

Utilize the exclamation mark operation for checking:

document.addEventListener("scroll", e => {
  let scrolled = document.scrollingElement!.scrollTop;
  ...
});

Answer 3

Answer №2

In my opinion, using a null check guard clause is the most effective approach.

useEffect (()=>{
   document.addEventListener("scroll", e => {
   let scrolled = document.scrollingElement.scrollTop;
   if (scrolled === null) {
      return;
   }
   if (scrolled >= 5){
      setPos("moved")
   } else {
      setPos("top")
    }
 })
},[])

Answer 4

In my opinion, using a null check guard clause is the most effective approach.

useEffect (()=>{
   document.addEventListener("scroll", e => {
   let scrolled = document.scrollingElement.scrollTop;
   if (scrolled === null) {
      return;
   }
   if (scrolled >= 5){
      setPos("moved")
   } else {
      setPos("top")
    }
 })
},[])

Answer 5

Answer №3

Simply ensure to handle the null scenario

useEffect(() => {
  document.addEventListener("scroll", e => {
    if (document.scrollingElement !== null) {
      const scrolled = document.scrollingElement.scrollTop;
      if (scrolled >= 5) {
        setPos("moved")
      } else {
        setPos("top")
      }
    }
  })
}, [])

Answer 6

Simply ensure to handle the null scenario

useEffect(() => {
  document.addEventListener("scroll", e => {
    if (document.scrollingElement !== null) {
      const scrolled = document.scrollingElement.scrollTop;
      if (scrolled >= 5) {
        setPos("moved")
      } else {
        setPos("top")
      }
    }
  })
}, [])

Tips on preventing Typescript error TS2531 related to potentially null objects

Answer №1

Answer №2

Answer №3

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