Thank you so much for this package - it's great!

Your changelog for 4.0.0 say "the sizes object can now be either null, or an object with numeric width and height properties (never null)", but the types defined in src/index.d.ts still declares a type where the width and height properties can be null.

I think it should be something like:

declare module 'react-resize-aware' {
    const useResizeAware: <T = {width: number; height: number}>(customReporter?: (target: HTMLIFrameElement | null) => null | T) => [JSX.Element, null | T]
    export default useResizeAware
}

(Your current definition also declares that T extends object, but I didn't keep that in my suggestion above, because by my reading, if someone defined a customReporter function that returned something not an object, e.g. just a number, the javascript hook would be fine with it.)

Also, I note that your package.json doesn't define a types field pointing at dist/index.d.ts, which means that compilers and IDEs might not pick up on your .d.ts file. It would be great if you could add that, too.

Thanks again!