[category- help] .on('end', ...) not waiting till process inside .on('data', ...) is completed.

[suraj-ingle]

here is the flow of code for what i am doing

const results = [];
fs.createReadStream('MainVerbs.csv')
    .pipe(csv())
    .on('data', async function (row) {
        await promiseReturningFunction(row['v1'])
    .on('end', () => {
        console.log('done'); 
    })

Problem is that, .on('end', ...) end is being fired before the time consuming processing on all rows is done.
I tried using async await in the .on('data', ...) section but it didn't make any difference

how do i work with this?

[jonah97]

I have kind of the same problem:

const results = []

fs.createReadStream('data.csv', 'binary')
    .pipe(csv({ separator: ';' }))
    .on('data', data => results.push(data))
    .on('end', () => {
        console.log(results.length)
    })

It reads the first 26442 rows and throws the 'end' event then. My file has 36000 rows. Don't know how to fix that...

[sumanth-mandalapu]

Is the result returned from the promise function used inside the on('data') function?

[m4rkus]

Have the same problem as the OP, seems that .on('end) is called before .on('data') has finished executing

[gdethier]

Using the close event instead of end solved the problem for me. Note that when using an async function for data processing, the stream has to be explicitly paused and resumed. Here is an example (in TypeScript, which is not far from JS anyway):

return new Promise<void>((resolve, reject) => {
    const stream = fs.createReadStream(path)
        .pipe(csv())
        .on("data", async data => {
            stream.pause();
            try {
                await processData(data);
            } finally {
                stream.resume();
            }
        })
        .on("error", error => reject(error))
        .on("close", () => resolve());
});

NB: More advanced error handling is probably needed around processData.