@wordpress/compose/build-module/hooks/use-resize-observer/use-resize-observer.js

WordPress higher-order components (HOCs).

/**
 * WordPress dependencies
 */
import { useRef } from '@wordpress/element';
/**
 * Internal dependencies
 */
import useEvent from '../use-event';

// This is the current implementation of `useResizeObserver`.
//
// The legacy implementation is still supported for backwards compatibility.
// This is achieved by overloading the exported function with both signatures,
// and detecting which API is being used at runtime.
export function useResizeObserver(callback, resizeObserverOptions = {}) {
  const callbackEvent = useEvent(callback);
  const observedElementRef = useRef();
  const resizeObserverRef = useRef();
  return useEvent(element => {
    var _resizeObserverRef$cu;
    if (element === observedElementRef.current) {
      return;
    }

    // Set up `ResizeObserver`.
    (_resizeObserverRef$cu = resizeObserverRef.current) !== null && _resizeObserverRef$cu !== void 0 ? _resizeObserverRef$cu : resizeObserverRef.current = new ResizeObserver(callbackEvent);
    const {
      current: resizeObserver
    } = resizeObserverRef;

    // Unobserve previous element.
    if (observedElementRef.current) {
      resizeObserver.unobserve(observedElementRef.current);
    }

    // Observe new element.
    observedElementRef.current = element;
    if (element) {
      resizeObserver.observe(element, resizeObserverOptions);
    }
  });
}
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