ndjson fetch API transformer

ndjson.js

const parseLine = (line) => {
    try {
        return JSON.parse(line);
    } catch (e) {
    }
};

const ucasefirst = (str) => str.charAt(0).toUpperCase() + str.slice(1);

/* A simple wrapper that will turn a fetch response into a streaming emitter of JSON objects
 * Usage:
 *  fetch(URI).then(response => ndjson(response)
 *      .on('data', data => {
 *          ...
 *      })
 *      .on('error', err => {
 *          ...
 *      })
 *      .on('end', () => {
 *          ...
 *      })
 *  })
 */
const ndjson = (response) => {
    const decoder = new TextDecoder();
    const reader = response.body.getReader();
    let buffer = '';
    const streamer = reader.read().then(function process(result) {
        if (result.done) {
            if (buffer.length > 0) {
                const result = parseLine(buffer);
                streamer.onData([result]);
            }
            streamer.onEnd();
            return;
        }
        buffer += decoder.decode(result.value, {stream: true});

        const lines = buffer.split("\n");
        buffer = lines.pop();
        const results = lines.filter(line => line.trim().length > 0).map(parseLine);
        if (results.length > 0) {
            streamer.onData(results);
        }
        return reader.read().then(process);
    }).catch((e) => {
        streamer.onError(e);
        reader.cancel();
        streamer.onEnd();
    });
    streamer.onData = streamer.onError = streamer.onEnd = () => {};
    streamer.on = (event, handler) => {
        streamer['on' + ucasefirst(event)] = handler;
        return streamer;
    };
    streamer.cancel = () => {
        reader.cancel();
        streamer.onEnd();
    };
    return streamer;
};

export default ndjson;