Ytukyg

Calling the readCSV from index.js

const productIds = await readCSV();

in another file:

async function readCSV() {

        const filepath = path.resolve('src/input_csv.csv');

        const readstream = await fs.createReadStream(filepath);

        const stream = await readstream.pipe(parser());

        let productIds = ;

        await stream.on('data', data => {

            productIds.push(data.SourceProductId);

            console.log('SourceProductId', data.SourceProductId);

        });

        await stream.on('end', () => {

            console.log(productIds);

        });

        if (productIds.length > 0) return productIds;

        else return 'no products found';

    });

}

it is giving the output:

in main: 

SourceProductId 1000050429

SourceProductId 1132353

SourceProductId 999915195

SourceProductId 50162873

SourceProductId 1000661087

[ '1000050429', '1132353', '999915195', '50162873', '1000661087' ]

I'm expecting the function to return an array of all values read from CSV. but the seems like it is returning before executing the stream.on statement. How to make sure all lines are executed before returning. I placed await before every statement but no luck

stream.on doesn't return a promise, so you cannot await it.

You can work around this by returning a promise from your readCSV function:

function readCSV() {

    return new Promise(resolve => {

        const filepath = path.resolve('src/input_csv.csv');

        const readstream = fs.createReadStream(filepath);

        const stream = readstream.pipe(parser());

        let productIds = ;

        stream.on('data', data => {

            productIds.push(data.SourceProductId);

            console.log('SourceProductId', data.SourceProductId);

        });

        stream.on('end', () => {

            console.log(productIds);

            if (productIds.length > 0) resolve(productIds);

            else resolve('no products found');

        });



    });

}

You create a promise by passing a callback function as argument. That callback function gets an argument resolve, which is a another callback function that you call when your asynchronous operation is done, passing the result.

In the example above, we call this resolve callback with the product IDs after the file read stream has finished.

Since readCSV now returns a promise, you can await it like you did in your code example:

const productIds = await readCSV();