useEffect 不会 go 到 if 语句

Question

Do not actually understand why this code part not working as it should. This useEffect block re-renders on every scrollY position. Also, I see that this code part: console.log(wrapperRef.current.style.opacity); should call if and else if statements, but it does not.

Here is the code:

 useEffect(() => { console.log(wrapperRef.current.style.opacity); if (wrapperRef.current.style.opacity === 0) { setIsHidden(true); console.log("true"); } else if (wrapperRef.current.style.opacity === 1) { setIsHidden(false); console.log("false"); } }, [position]);

Answer 1

As you can see here, style values are strings, but with the === operator you also check for type equality.

This means you check that '0' === 0 which are not the same types and also why your check never enters the if body.

Either check for '0' or use the == operator which does ignore types.