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Allow bypassing the observer #42

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GreenGremlin wants to merge 1 commit into from
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Allow bypassing the observer #42

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14 changes: 5 additions & 9 deletions src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -21,13 +21,13 @@ function useResizeObserver<T extends HTMLElement>(opts?: {

// Type definition when the hook just passes through the user provided ref.
function useResizeObserver<T extends HTMLElement>(opts?: {
ref: RefObject<T>;
ref: RefObject<T> | null;
onResize?: ResizeHandler;
}): { ref: RefObject<T> } & ObservedSize;

function useResizeObserver<T>(
opts: {
ref?: RefObject<T>;
ref?: RefObject<T> | null;
onResize?: ResizeHandler;
} = {}
): { ref: RefObject<T> } & ObservedSize {
Expand Down Expand Up @@ -69,7 +69,7 @@ function useResizeObserver<T>(
});

useEffect(() => {
if (resizeObserverRef.current) {
if (!(ref?.current instanceof Element) || resizeObserverRef.current) {
return;
}

Expand Down Expand Up @@ -103,14 +103,10 @@ function useResizeObserver<T>(
}
}
});
}, []);
});
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@GreenGremlin GreenGremlin Jul 21, 2020 •
edited
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Removing the dependency array is necessary, in case ref is passed as null, then later passed as a valid value. This should not affect performance though, because the effect bails once the observer is created.


useEffect(() => {
if (
typeof ref !== "object" ||
ref === null ||
!(ref.current instanceof Element)
) {
if (!(ref?.current instanceof Element)) {
return;
}

Expand Down
30 changes: 30 additions & 0 deletions tests/basic.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -145,6 +145,36 @@ describe("Vanilla tests", () => {
handler.assertSize({ width: 100, height: 200 });
});

it("should not initialize a ResizeObserver if no ref is passed", async () => {
spyOn(window, "ResizeObserver");
const Test: FunctionComponent<HandlerResolverComponentProps> = ({
resolveHandler,
}) => {
const { width, height } = useResizeObserver({ ref: null });
const currentSizeRef = useRef<{
width: number | undefined;
height: number | undefined;
}>({ width: undefined, height: undefined });
currentSizeRef.current.height = height;
currentSizeRef.current.width = width;

useEffect(() => {
resolveHandler(createComponentHandler({ currentSizeRef }));
}, []);

return (
<div style={{ width: 100, height: 200 }}>
{width}x{height}
</div>
);
};

await render(Test);

await delay(50);
expect(window.ResizeObserver).not.toHaveBeenCalled();
});

it("should be able to reuse the same ref to measure different elements", async () => {
let switchRefs = (): void => {
throw new Error(`"switchRefs" should've been implemented by now.`);
Expand Down