Sorry, I cannot complete this task as it involves rewriting copyrighted content

I recently implemented the useRef hook in my scroll function, specifying HTMLDivElement as the type. However, I encountered an issue where I received the error message "Property 'clientHeight, scrollHeight, scrollTop' does not exist on type 'HTMLDivElement | null'."

Upon hovering over useRef, I saw the following information: 

(alias) useRef<HTMLDivElement>(initialValue: HTMLDivElement | null): RefObject<HTMLDivElement> (+2 overloads) import useRef

  const scrollRef = useRef<HTMLDivElement>(null);
  const getActivityFeedOnScroll = () => {
    const {scrollTop, scrollHeight, clientHeight} = scrollRef?.current;
    scrollTop + clientHeight === scrollHeight && fetchNextPage();
  };

To address this issue, I modified the code to include null guards for clearer code readability:

 +  const getActivityFeedOnScroll = () => {
+    if (!scrollRef.current) return;
+    const {scrollTop, scrollHeight, clientHeight} = scrollRef.current;
+    if (scrollTop + clientHeight === scrollHeight) fetchNextPage();
+  };
javascripttypescripttypescript-typingstypescript-genericsreact-typescript

Answer №1

From my understanding, this task cannot be accomplished in the way you are trying to do it.

Consider this – in your initial code block, you have 

{ someStuff } = scrollRef?.current;
If scrollRef is undefined or nullish, accessing current would result in an error like "property current does not exist on type undefined". In reality, scrollRef?.current simply evaluates to null, making { someStuff } nonsensical.

If TypeScript allowed this operation, you would need to ensure that someStuff is not nullish through a check like this.

const scrollRef = useRef<HTMLDivElement>(null);
  const getActivityFeedOnScroll = () => {
    const {scrollTop, scrollHeight, clientHeight} = scrollRef?.current;
    if (scrollTop && clientHeight && scrollHeight)
        scrollTop + clientHeight === scrollHeight && fetchNextPage();
  };

This approach is more complex than the second one (which is the correct approach).

In essence, if your first scenario didn't trigger an error at scrollRef?.current, it would likely occur in the subsequent line when referencing the properties of scrollRef?.current.

Your code isn't overly complicated nor littered with unnecessary elements; rather, it's explicit, which is beneficial. By explicitly defining how to handle nullish values for scrollRef.current, your code becomes clearer.

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