quadstore/dist/utils/consumeonebyone.js

Quadstore is a LevelDB-backed RDF graph database / triplestore for JavaScript runtimes (browsers, Node.js, Deno, Bun, ...) that implements the RDF/JS interfaces and supports SPARQL queries and querying across named graphs.

export const consumeOneByOne = async (source, onEachItem) => {
    return new Promise((resolve, reject) => {
        let item;
        let ended = false;
        let looping = false;
        const loop = () => {
            looping = true;
            if ((item = source.read()) !== null) {
                Promise.resolve(onEachItem(item))
                    .then(loop)
                    .catch(onError);
                return;
            }
            looping = false;
            if (ended) {
                resolve();
            }
        };
        const onError = (err) => {
            reject(err);
            cleanup();
        };
        const onEnd = () => {
            ended = true;
            if (!looping) {
                resolve();
            }
            cleanup();
        };
        const onReadable = () => {
            if (!looping) {
                loop();
            }
        };
        const cleanup = () => {
            source.removeListener('end', onEnd);
            source.removeListener('error', onError);
            source.removeListener('readable', onReadable);
            source.destroy?.();
        };
        source.on('end', onEnd);
        source.on('error', onError);
        source.on('readable', onReadable);
        if ('readable' in source && source.readable) {
            loop();
        }
    });
};
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