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import type {
UseResizeObserverOptions,
UseResizeObserverReturn,
ResizeEntry,
OnResizeCallback,
OnErrorCallback,
ResizeObserverBoxOptions,
} from "./types";
import {
isResizeObserverSupported,
toResizeEntry,
extractSize,
createInitialResizeEntry,
createNoopRef,
validateOptions,
hasSizeChanged,
} from "./utils";
/**
* React hook for observing element size changes using ResizeObserver API.
*
* Features:
* - Real-time element size tracking (width, height)
* - Support for border-box, content-box, device-pixel-content-box
* - Debounce/Throttle options for performance optimization
* - Custom rounding function for dimension values
* - Callback and state-based modes
* - SSR compatible with graceful degradation
* - TypeScript support with full type inference
*
* @param options - Configuration options for the observer
* @returns Object containing dimensions, ref callback, and control methods
*
* @example
* ```tsx
* // Basic usage - track element dimensions
* function Component() {
* const { ref, width, height } = useResizeObserver();
* return (
* <div ref={ref}>
* Size: {width}px x {height}px
* </div>
* );
* }
* ```
*
* @example
* ```tsx
* // With debounce for performance
* function DebouncedComponent() {
* const { ref, width, height } = useResizeObserver({
* debounce: 100,
* onResize: (entry) => console.log('Resized:', entry),
* });
* return <div ref={ref}>{width} x {height}</div>;
* }
* ```
*
* @example
* ```tsx
* // Border-box sizing
* function BorderBoxComponent() {
* const { ref, borderBoxSize } = useResizeObserver({
* box: 'border-box',
* });
* return (
* <div ref={ref} style={{ padding: 20 }}>
* Border: {borderBoxSize?.inlineSize} x {borderBoxSize?.blockSize}
* </div>
* );
* }
* ```
*
* @example
* ```tsx
* // Callback-only mode (no state updates)
* function CallbackOnlyComponent() {
* const { ref } = useResizeObserver({
* updateState: false,
* onResize: (entry) => {
* // Direct DOM manipulation for animations
* entry.target.style.setProperty('--width', `${entry.contentRect.width}px`);
* },
* });
* return <div ref={ref}>Animation container</div>;
* }
* ```
*/
export function useResizeObserver<T extends Element = Element>(
options: UseResizeObserverOptions<T> = {}
): UseResizeObserverReturn<T> {
const {
box = "content-box",
debounce,
throttle,
round = Math.round,
onResize,
onError,
updateState = true,
enabled = true,
initialWidth,
initialHeight,
} = options;
// ============ Validation ============
validateOptions(debounce, throttle);
// ============ SSR Check ============
const isSupported = isResizeObserverSupported();
// ============ Refs ============
const observerRef = useRef<ResizeObserver | null>(null);
const targetRef = useRef<T | null>(null);
const onResizeRef = useRef<OnResizeCallback | undefined>(onResize);
const onErrorRef = useRef<OnErrorCallback | undefined>(onError);
const debounceRef = useRef<number | undefined>(debounce);
const throttleRef = useRef<number | undefined>(throttle);
const debounceTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
const throttleTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
const lastThrottleTimeRef = useRef<number>(0);
const isObservingRef = useRef<boolean>(false);
const prevSizeRef = useRef<{ width: number; height: number } | null>(null);
// Update refs on each render to get latest values
onResizeRef.current = onResize;
onErrorRef.current = onError;
debounceRef.current = debounce;
throttleRef.current = throttle;
// ============ State ============
const [state, setState] = useState<{
width: number | undefined;
height: number | undefined;
entry: ResizeEntry | undefined;
}>(() => ({
width: initialWidth,
height: initialHeight,
entry: createInitialResizeEntry(initialWidth, initialHeight),
}));
const [isObserving, setIsObserving] = useState<boolean>(false);
// ============ Handle Resize (Core Logic) ============
const handleResize = useCallback(
(entries: ResizeObserverEntry[]) => {
// Process all entries (for multiple element observation)
for (const entry of entries) {
try {
const resizeEntry = toResizeEntry(entry);
// Call onResize callback for each entry
if (onResizeRef.current) {
onResizeRef.current(resizeEntry);
}
} catch (error) {
Eif (onErrorRef.current) {
onErrorRef.current(error as Error);
}
}
}
// Update state with the last entry (for single element mode via ref)
const lastEntry = entries[entries.length - 1];
Iif (!lastEntry) return;
try {
const resizeEntry = toResizeEntry(lastEntry);
const { width, height } = extractSize(lastEntry, box, round);
// Update state if enabled and size changed
if (updateState) {
const prevSize = prevSizeRef.current;
if (
!prevSize ||
hasSizeChanged(prevSize.width, prevSize.height, width, height)
) {
prevSizeRef.current = { width, height };
setState({ width, height, entry: resizeEntry });
}
}
} catch (error) {
if (onErrorRef.current) {
onErrorRef.current(error as Error);
}
}
},
[box, round, updateState]
);
// ============ Process Resize (with Debounce/Throttle) ============
const processResize = useCallback(
(entries: ResizeObserverEntry[]) => {
// Clear existing debounce timeout
if (debounceTimeoutRef.current) {
clearTimeout(debounceTimeoutRef.current);
debounceTimeoutRef.current = null;
}
// Use refs to get latest debounce/throttle values
const debounceDelay = debounceRef.current ?? 0;
const throttleInterval = throttleRef.current ?? 0;
if (debounceDelay > 0) {
// Debounce mode
debounceTimeoutRef.current = setTimeout(() => {
handleResize(entries);
debounceTimeoutRef.current = null;
}, debounceDelay);
} else if (throttleInterval > 0) {
// Throttle mode
const now = Date.now();
const timeSinceLastCall = now - lastThrottleTimeRef.current;
if (timeSinceLastCall >= throttleInterval) {
lastThrottleTimeRef.current = now;
handleResize(entries);
} else if (!throttleTimeoutRef.current) {
// Schedule trailing call
throttleTimeoutRef.current = setTimeout(() => {
lastThrottleTimeRef.current = Date.now();
handleResize(entries);
throttleTimeoutRef.current = null;
}, throttleInterval - timeSinceLastCall);
}
} else {
// No debounce/throttle - immediate execution
handleResize(entries);
}
},
[handleResize] // Remove debounce/throttle from deps - use refs instead
);
// ============ Observer Callback ============
const observerCallbackRef = useRef<(entries: ResizeObserverEntry[]) => void>(
(entries) => processResize(entries)
);
observerCallbackRef.current = (entries) => processResize(entries);
// ============ Create Observer ============
const createObserver = useCallback(() => {
if (!isSupported) return;
// Disconnect existing observer
if (observerRef.current) {
observerRef.current.disconnect();
observerRef.current = null;
}
// Create new observer with ref-based callback for stability
observerRef.current = new ResizeObserver((entries) => {
observerCallbackRef.current(entries);
});
// Observe current target if exists and enabled
if (targetRef.current && enabled) {
observerRef.current.observe(targetRef.current, { box });
isObservingRef.current = true;
setIsObserving(true);
}
}, [isSupported, enabled, box]);
// ============ Ref Callback ============
const setRef = useCallback(
(node: T | null) => {
const prevTarget = targetRef.current;
// Skip if same element (prevent redundant observe calls)
if (node === prevTarget) {
return;
}
// Unobserve previous target
if (prevTarget && observerRef.current) {
observerRef.current.unobserve(prevTarget);
}
targetRef.current = node;
// Observe new target
if (node && observerRef.current && enabled) {
observerRef.current.observe(node, { box });
isObservingRef.current = true;
setIsObserving(true);
} else {
isObservingRef.current = false;
setIsObserving(false);
}
},
[box, enabled]
);
// ============ Manual Control Methods ============
const observe = useCallback(
(element: T) => {
Iif (!isSupported) return;
// Create observer if it doesn't exist yet
Iif (!observerRef.current) {
observerRef.current = new ResizeObserver((entries) => {
observerCallbackRef.current(entries);
});
}
observerRef.current.observe(element, { box });
isObservingRef.current = true;
setIsObserving(true);
},
[isSupported, box]
);
const unobserve = useCallback((element: T) => {
Iif (!observerRef.current) return;
observerRef.current.unobserve(element);
// Check if still observing other elements
// For simplicity, we set to false (single element mode)
isObservingRef.current = false;
setIsObserving(false);
}, []);
const disconnect = useCallback(() => {
Iif (!observerRef.current) return;
observerRef.current.disconnect();
observerRef.current = null;
isObservingRef.current = false;
setIsObserving(false);
}, []);
// ============ Effect: Create Observer on Mount ============
useEffect(() => {
Iif (!isSupported) return;
// Create observer with ref-based callback (only once on mount)
observerRef.current = new ResizeObserver((entries) => {
observerCallbackRef.current(entries);
});
// Observe current target if exists and enabled
Iif (targetRef.current && enabled) {
observerRef.current.observe(targetRef.current, { box });
isObservingRef.current = true;
setIsObserving(true);
}
return () => {
// Cleanup timeouts
if (debounceTimeoutRef.current) {
clearTimeout(debounceTimeoutRef.current);
debounceTimeoutRef.current = null;
}
if (throttleTimeoutRef.current) {
clearTimeout(throttleTimeoutRef.current);
throttleTimeoutRef.current = null;
}
// Disconnect observer
if (observerRef.current) {
observerRef.current.disconnect();
observerRef.current = null;
}
isObservingRef.current = false;
};
// Note: Only depend on isSupported to create observer once on mount
// enabled and box changes are handled separately to avoid re-creating observer
// eslint-disable-next-line react-hooks/exhaustive-deps
}, [isSupported]);
// ============ Effect: Handle enabled toggle ============
useEffect(() => {
if (!isSupported || !observerRef.current || !targetRef.current) return;
if (enabled && !isObservingRef.current) {
// Only observe if not already observing
observerRef.current.observe(targetRef.current, { box });
isObservingRef.current = true;
setIsObserving(true);
E} else if (!enabled && isObservingRef.current) {
// Only unobserve if currently observing
observerRef.current.unobserve(targetRef.current);
isObservingRef.current = false;
setIsObserving(false);
}
}, [enabled, isSupported, box]);
// ============ Computed Values ============
const computedValues = useMemo(
() => ({
contentRect: state.entry?.contentRect,
borderBoxSize: state.entry?.borderBoxSize?.[0],
contentBoxSize: state.entry?.contentBoxSize?.[0],
devicePixelContentBoxSize: state.entry?.devicePixelContentBoxSize?.[0],
}),
[state.entry]
);
// ============ SSR Return ============
Iif (!isSupported) {
return {
ref: createNoopRef<T>(),
width: initialWidth,
height: initialHeight,
entry: createInitialResizeEntry(initialWidth, initialHeight),
contentRect: undefined,
borderBoxSize: undefined,
contentBoxSize: undefined,
devicePixelContentBoxSize: undefined,
isSupported: false,
isObserving: false,
observe: () => {},
unobserve: () => {},
disconnect: () => {},
};
}
// ============ Client Return ============
return {
ref: setRef,
width: state.width,
height: state.height,
entry: state.entry,
...computedValues,
isSupported,
isObserving,
observe,
unobserve,
disconnect,
};
}
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