Node CSV pull parser - node.js

Question

I need to parse a CSV document from Node.JS, performing database operations for each record (= each line). However, I'm having trouble finding a suitable CSV parser using a pull approach, or at least a push approach that waits for my record operations before parsing the next row.
I've looked at csv-parse, csvtojson, csv-streamify, but they all seem to push events in a continuous stream without any flow control. If parsing a 1000 line CSV document, I basically get all 1000 callbacks in quick sequence. For each record, I perform an operation returning a promise. Currently I've had to resort to pushing all my promises into an array and after getting the done/end event I also wait for Promise.all(myOperations) to know when the document has been fully processed. But this is not very nice, and also, I'd prefer parsing one line at a time and fully processing it, before getting the next record, instead of concurrently processing all records - it's hard to debug and uses a lot of memory as opposed to simply dealing with each record sequentially.
So, is there a CSV parser that supports pull mode, or a way to get any stream-based CSV parser (preferably csvtojson as that's the one I'm using at the moment) to only produce events for new records when my handler for the previous record is finished (using promises)?

Answer 1

I solved this myself by creating my own Writable and piping the CSV parser to it. My write method does its stuff and wraps a promise to the node callback passed to _write() (here implemented using Q.nodeify):
class CsvConsumer extends stream.Writable {
_write(data, encoding, cb) {
console.log('Got data: ', data);
Q.delay(1000).then(() => {
console.log('Waited 1 s');
}).nodeify(cb);
}
}
csvtojson()
.fromStream(is)
.pipe(new CsvConsumer())
.on('finish', err => {
if (err) {
console.log('Error!');
} else {
console.log('Done!');
}
});
This will process lines one by one:
Got data: {"a": "1"}
Waited 1 s
Got data: {"a": "2"}
Waited 1 s
Got data: {"a": "3"}
Waited 1 s
Done!

Answer 2

If you want to process each line asynchronously you can do that with node's native LineReader.
const lineStream = readline.createInterface({
input: fs.createReadStream('data/test.csv'),
});
lineStream.on('line', (eachLine) =>{
//process each line
});
If you want to do the same in synchronous fashion you can use line-by-line. It doesn't buffer the entire file into memory. It provides event handlers to pause and resume the 'line' emit event.
lr.on('line', function (line) {
// pause emitting of lines...
lr.pause();
// ...do your asynchronous line processing..
setTimeout(function () {
// ...and continue emitting lines. (1 sec delay)
lr.resume();
}, 1000);
});