# All files / src useResizeObserver.ts

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100% Branches 29/29
100% Functions 6/6
100% Lines 235/235

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     "use client";
    import { useEffect, type Ref, type RefCallback } from "react";
    import { useEnsuredRef } from "./useEnsuredRef.js";

    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    import { type useElementSize } from "./useElementSize.js";

    /**
     * @remarks \@since 6.0.0
     */
    export type ResizeObserverEntryCallback = (entry: ResizeObserverEntry) => void;

    /** @internal */
    type Unsubscribe = () => void;

    /** @internal */
    interface TargetSize {
      height: number;
      width: number;
      scrollHeight: number;
      scrollWidth: number;
    }

    /** @internal */
    interface TargetSubscription {
      readonly onUpdate: ResizeObserverEntryCallback;
      readonly disableHeight: boolean;
      readonly disableWidth: boolean;

      size?: TargetSize;
    }

    /** @internal */
    interface SubscribeOptions {
      element: Element;
      onUpdate: ResizeObserverEntryCallback;
      disableHeight: boolean;
      disableWidth: boolean;
    }

    /**
     * @internal
     * @remarks \@since 6.0.0 This was added to help with testing. The
     * `subscriptions` and `sharedObserver` used to be module-level variables but
     * moving to a class makes it easier to mock. Checkout the
     * `src/tests-utils/ResizeObserver.ts`
     */
    export class ResizeObserverManager {
      frame: number;
      subscriptions: Map<Element, Set<TargetSubscription>>;

      /**
       * Why is there a single shared observer instead of multiple and a
       * "subscription" model?
       *
       * Note: Probably a bit of a premature optimization right now...
       *
       * @see https://github.com/WICG/resize-observer/issues/59
       * @internal
       */
      sharedObserver: ResizeObserver | undefined;

      constructor() {
        this.frame = 0;
        this.subscriptions = new Map();
      }

      subscribe = (options: SubscribeOptions): Unsubscribe => {
        const { element, onUpdate, disableHeight, disableWidth } = options;

        // lazy initialize the observer
        const observer =
          this.sharedObserver ||
          new ResizeObserver((entries) => {
            // this prevents the `ResizeObserver loop limit exceeded`
            window.cancelAnimationFrame(this.frame);
            this.frame = window.requestAnimationFrame(() => {
              this.handleResizeEntries(entries);
            });
          });
        this.sharedObserver = observer;

        const updates = this.subscriptions.get(element) || new Set();
        const subscription: TargetSubscription = {
          onUpdate,
          disableHeight,
          disableWidth,
        };
        updates.add(subscription);
        if (!this.subscriptions.has(element)) {
          this.subscriptions.set(element, updates);
        }

        observer.observe(element);

        return () => {
          observer.unobserve(element);
          updates.delete(subscription);
        };
      };

      handleResizeEntries = (entries: ResizeObserverEntry[]): void => {
        for (const entry of entries) {
          const targetSubscriptions = this.subscriptions.get(entry.target);
          // shouldn't really happen
          /* c8 ignore start */
          if (!targetSubscriptions) {
            continue;
          }
          /* c8 ignore end */

          const entries = targetSubscriptions.values();
          for (const subscription of entries) {
            const { height, width } = entry.contentRect;
            const { scrollHeight, scrollWidth } = entry.target;
            const { onUpdate, size, disableHeight, disableWidth } = subscription;
            const isHeightChange =
              !disableHeight &&
              (!size ||
                size.height !== height ||
                size.scrollHeight !== scrollHeight);
            const isWidthChange =
              !disableWidth &&
              (!size || size.width !== width || size.scrollWidth !== scrollWidth);

            subscription.size = {
              height,
              width,
              scrollHeight,
              scrollWidth,
            };
            if (isHeightChange || isWidthChange) {
              onUpdate(entry);
            }
          }
        }
      };
    }

    /**
     * @internal
     * @remarks \@since 6.0.0
     */
    export const resizeObserverManager = new ResizeObserverManager();

    /**
     * @remarks
     * \@since 2.3.0
     * \@since 6.0.0 Renamed from `UseResizeObserverOptions` and added
     * `onUpdate`/`disabled` options.
     */
    export interface ResizeObserverHookOptions<E extends HTMLElement> {
      /**
       * An optional ref to merge with the ref returned by this hook.
       */
      ref?: Ref<E>;

      /**
       * **Must be wrapped in `useCallback` to prevent re-creating the
       * ResizeObserver each render.**
       *
       * This function will be called whenever the target element resizes.
       *
       * @see {@link useResizeObserver} for an example.
       */
      onUpdate: ResizeObserverEntryCallback;

      /**
       * Set this to `true` to prevent observing the element's size changes. THis is
       * equivalent to not attaching the returned ref to any element.
       *
       * @defaultValue `false`
       */
      disabled?: boolean;

      /**
       * Set this to `true` if the {@link onUpdate} should not be fired for height
       * changes.
       *
       * @defaultValue `false`
       */
      disableHeight?: boolean;

      /**
       * Set this to `true` if the {@link onUpdate} should not be fired for width
       * changes.
       *
       * @defaultValue `false`
       */
      disableWidth?: boolean;
    }

    /**
     * The resize observer is used to track the size changes of a specific element.
     * For most cases you can use the {@link useElementSize} instead, but this hook
     * can be used for more complex behavior with the {@link ResizeObserverEntry}.
     *
     * @remarks
     * \@since 2.3.0
     * \@since 6.0.0 The API was updated to match the `useIntersectionObserver`
     * implementation -- accepts only a single object parameter and returns a
     * {@link RefCallback} instead of `[nodeRef, refCallback]`
     */
    export function useResizeObserver<E extends HTMLElement>(
      options: ResizeObserverHookOptions<E>
    ): RefCallback<E> {
      const {
        ref,
        onUpdate,
        disabled,
        disableHeight = false,
        disableWidth = false,
      } = options;

      const [targetNodeRef, refCallback] = useEnsuredRef(ref);
      useEffect(() => {
        const element = targetNodeRef.current;
        if (disabled || (disableHeight && disableWidth) || !element) {
          return;
        }

        const unsubscribe = resizeObserverManager.subscribe({
          element,
          onUpdate,
          disableHeight,
          disableWidth,
        });

        return () => {
          unsubscribe();
        };
      }, [disableHeight, disableWidth, disabled, onUpdate, targetNodeRef]);

      return refCallback;
    }