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.

Answer 1

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
 });

• Mehdi Bahlaoui: 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: @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: I have posted another question stackoverflow.com/questions/72099168/csv-parser-onend-nodejs Thank you.

Answer 2

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);
 });
});