@pdftron/webviewer-react-toolkit/lib/hooks/useFileSubscribe.js

A React component library for integrating with PDFTron WebViewer API.

import { useEffect, useMemo, useRef, useState } from 'react';
import { MemoizedPromise } from '../data';
import GlobalQueue from '../work/GlobalQueue';
/**
 * Will subscribe to a value from a file and return the value, as well as any
 * async errors.
 * @param file The file to subscribe to.
 * @param getCurrentValue Function to extract the current value from the file.
 * @param eventType The event type to subscribe. Won't subscribe if not given.
 * @param throttle The timeout to throttle initial fetch of value. Default: 500ms.
 */
export function useFileSubscribe(file, getCurrentValue, eventType) {
    const getValue = useRef(getCurrentValue);
    const [error, setError] = useState();
    const [value, setValue] = useState(() => {
        const currentValue = getValue.current(file);
        if (currentValue instanceof MemoizedPromise)
            return undefined;
        return currentValue;
    });
    useEffect(() => {
        let cancelled = false;
        let cancel;
        const setMemoValue = (val) => {
            try {
                if (!cancelled)
                    setValue(val);
            }
            catch (error) {
                if (!cancelled)
                    setError(error);
            }
        };
        const subscribe = () => {
            setError(undefined);
            const val = getValue.current(file);
            if (!(val instanceof MemoizedPromise)) {
                // Non-memoized-promise, can set directly.
                setValue(val);
                return;
            }
            setValue(undefined);
            if (val.done) {
                val.get().then(setMemoValue);
            }
            else {
                const r = GlobalQueue.process(() => val.get());
                cancel = r[1];
                r[0]
                    .then((result) => {
                    setMemoValue(result);
                })
                    .catch((e) => {
                    setError(e);
                });
            }
        };
        subscribe();
        let unsubscribe;
        if (eventType)
            unsubscribe = file.subscribe(eventType, subscribe);
        return () => {
            cancel?.();
            unsubscribe?.();
            cancelled = true;
        };
    }, [eventType, file]);
    return useMemo(() => [value, error, setValue], [error, value]);
}