Parse csv using "csv-parser" node JS

Question

I am using the 'csv-parser' library. Using the method below I am able to get the data stored in the birthdays array shown in the console:

    const birthdays = [];  
fs.createReadStream('./data/groupes.csv')
        .pipe(csv({}))
        .on('data', (data) => birthdays.push(data))
        .on('end', () => {
          console.log(birthdays)
      });

but when I log outside the .on('end') like below, the console shows the birthdays array as empty:

    const birthdays = [];  
fs.createReadStream('./data/groupes.csv')
        .pipe(csv({}))
        .on('data', (data) => birthdays.push(data))
        .on('end', () => {
      });
      console.log(birthdays)

Why is that? and how can I solve it? Thanks in advance.

Aneesh · Accepted Answer · 2022-05-01 21:10:41Z

2

Why is that?

It's because createReadStream is working asynchronously and when you console.log(birthdays); outside, the code execution reads the log before createReadStream has finished processing

how can I solve it?

You were correct to put it inside the .on("end")

const birthdays = [];  
fs.createReadStream('./data/groupes.csv')
    .pipe(csv({}))
    .on('data', (data) => birthdays.push(data))
    .on('end', () => {
      console.log(birthdays);
      // further processing with birthdays
  });

answered May 1, 2022 at 21:10

Aneesh

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3 Comments

Mehdi Bahlaoui Over a year ago

As a follow up question, I am trying to assign a value of a variable already declared inside the .on('end') part but it doesn't work for some reason, any idea why?

Aneesh Over a year ago

@Mehdi I would be able to help if you could share how you are declaring the variable and what exactly isn't working (eg, if there is an error)

Mehdi Bahlaoui Over a year ago

I have posted another question stackoverflow.com/questions/72099168/csv-parser-onend-nodejs Thank you.

PCDSandwichMan · Accepted Answer · 2022-05-01 21:07:49Z

0

Could you do something like this?

const csv = require("csv-parser");
const fs = require("fs");
const path = require("path");
const { promisify } = require("util");
const readFile = promisify(fs.readFile);

const birthdays = [];

const filePath = path.join(__dirname, "data", "groupes.csv");

readFile(filePath, "utf8").then((data) => {
  csv(data, {
    separator: ",",
  })
    .on("data", (row) => {
      birthdays.push(row);
    })
    .on("end", () => {
      console.log(birthdays);
    });
});

answered May 1, 2022 at 21:07

PCDSandwichMan

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