Iterate over CSV file and run await for each row?

问题

I want to iterate over a CSV file in node, and for each row, call an asynchronous function and wait for it to complete.

How can I do this?

I have:

const getFile = async function(url) {
    const response = await page.goto(url, { waitUntil: 'networkidle2' });
    await page.waitFor(3000);
    const ad = await page.waitForSelector('div.chart');
    await ad.screenshot({
        path: path
    });
};

fs.createReadStream(fname)
    .pipe(csv())
    .on('data', (row) => {
        let id = row.ad_id;
        let url = 'xxxx' + id;
        await getFile(path);
    }).on('end', () => {
        console.log('CSV file successfully processed');
    });

But this gives me SyntaxError: await is only valid in async function, throwing the error on the await getFile(path); line.

回答1:

You're getting a SyntaxError because, as it says, await is only valid in an async function. You can fix this by making your callback async, but that alone won't cause the pipe to stop emitting further data events until the async function finishes. You can probably, however, do this manually like so:

const csvPipe = fs.createReadStream(fname).pipe(csv());
csvPipe.on('data', async (row) => {
        csvPipe.pause();
        let id = row.ad_id;
        let url = 'xxxx' + id;
        await getFile(path);
        csvPipe.resume();
    }).on('end', () => {
        console.log('CSV file successfully processed');
    });

回答2:

Since the getFile function is already a promise, you can pause and resume the pipe using the promise functions and without making the function async.

const csvPipe = fs.createReadStream(fname).pipe(csv());
csvPipe.on('data', (row) => {
    csvPipe.pause();
    let id = row.ad_id;
    let url = 'xxxx' + id;
    getFile(path).finally(() => csvPipe.resume());
}).on('end', () => {
    console.log('CSV file successfully processed');
});

来源：https://stackoverflow.com/questions/59976549/iterate-over-csv-file-and-run-await-for-each-row