I'm storing a reference to an image item using: const renderedImageRef = useRef(). The ref is then assigned in render() function using:
<img ref={renderedImageRef} src=... />
In another JSX item below, I try to access renderedImageRef.current.clientHeight using:
<div style={{top:`${renderedImageRef.current.clientHeight}px`}}>
Hello world
</div>
But this produces an error in the console:
Uncaught TypeError: Cannot read properties of undefined (reading 'clientHeight')
Strangely enough, if I try to access renderedImageRef.current.clientHeight from inside a useEffect hook, it displays the height correctly:
useEffect(() => {
if(renderedImageRef !== null) {
console.log(renderedImageRef)
}
}, [renderedImageRef])
Why am I getting the console error?
A possible answer is that this line:
<div style={{top:`${renderedImageRef.current.clientHeight}px`}}>Hello world</div>
is coming in your code before this one:
<img ref={renderedImageRef} src=... />
In witch case it is normal that you are getting the error. It is to know that when you call const renderedImageRef = useRef(), the value of renderedImageRef is {current:undefined}. The JSX needs to be rendered before a ref gets its value in current field.
A solution is to use a state for the top:
const [top, setTop]=useState(0)
useEffect(() => {
if(renderedImageRef.current) {
setTop(renderedImageRef.current.clientHeight);
}
}, [renderedImageRef])
<div style={{top:`${top}px`}}>Hello world</div>
If you are using Next.JS, I think you have to change the dependency to renderedImageRef.current. So something like this:
const [top, setTop]=useState(0)
useEffect(() => {
if(renderedImageRef.current) {
setTop(renderedImageRef.current.clientHeight);
}
}, [renderedImageRef.current])