packages/chunked-file-reader/lib/formatters.js
function _toRecords(rawData, delimiter, slice) {
    // Since slices with a non-zero chunk offset grab the character
    // immediately preceding the main chunk, if one of those chunks has a
    // delimiter as the first or second character, it means the chunk starts
    // with a complete record. In this case as well as when the chunk begins
    // with a partial record, splitting the chunk into an array by its
    // delimiter will result in a single garbage record at the beginning of
    // the array. If the offset is 0, the array will never start with a
    // garbage record

    let outputData = rawData;
    if (rawData.endsWith(delimiter)) {
        // Get rid of last character if it is the delimiter since that will
        // just result in an empty record.
        outputData = rawData.slice(0, -delimiter.length);
    }

    if (slice.offset === 0) {
        return outputData.split(delimiter);
    }
    return outputData.split(delimiter).splice(1);
}
function _toRecords(rawData, delimiter, slice) {
    // Since slices with a non-zero chunk offset grab the character
    // immediately preceding the main chunk, if one of those chunks has a
    // delimiter as the first or second character, it means the chunk starts
    // with a complete record. In this case as well as when the chunk begins
    // with a partial record, splitting the chunk into an array by its
    // delimiter will result in a single garbage record at the beginning of
    // the array. If the offset is 0, the array will never start with a
    // garbage record

    let outputData = rawData;
    if (rawData.endsWith(delimiter)) {
        // Get rid of last character if it is the delimiter since that will
        // just result in an empty record.
        outputData = rawData.slice(0, -delimiter.length);
    }

    if (slice.offset === 0) {
        return outputData.split(delimiter);
    }
    return outputData.split(delimiter).splice(1);
}
This function takes the raw data and breaks it into records, getting rid of anything preceding the first complete record if the data does not start with a complete record.