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Node.js CSV Reading and Writing (with node-csv)

What Will You Learn in This Guide?​

This guide explains how to process CSV files efficiently with Node.js.
You learn stream-based reading and writing methods for large files.

Technical Summary​

  • Subject: Node.js CSV operations
  • Problem: Memory overflow with large CSV files
  • Solution: use node-csv + stream
  • Goal: Scalable data processing

How to Use CSV Files in Node.js?​

CSV files are plain text files that store tabular data.
Fields are usually separated by commas.

There are many CSV libraries for Node.js.
node-csv is suitable for large files with its stream-based structure.

Preparing the Project Environment​

mkdir csv_demo
cd csv_demo
npm init -y
npm install csv sqlite3
  • These commands install the project folder and necessary packages.

Using CSV Modules​


const { parse } = require("csv-parse");
const { stringify } = require("csv-stringify");
  • These modules are for CSV reading and writing operations.

Reading CSV File (via Stream)​


const fs = require("fs");
const { parse } = require("csv-parse");

fs.createReadStream("data.csv")
  .pipe(parse({ delimiter: ",", from_line: 2 }))
  .on("data", (row) => {
    console.log(row);
  });
  • This code reads the CSV file line by line.

Reading CSV as Object​


fs.createReadStream("data.csv")
  .pipe(parse({ columns: true, trim: true }))
  .on("data", (row) => {
    console.log(row.year_month);
  });
  • This setting uses the first line as the title.

Secure Reading with async/await


async function oku() {
  const parser = fs
    .createReadStream("data.csv")
    .pipe(parse({ columns: true }));

  for await (const row of parser) {
    console.log(row);
  }
}
  • This method prevents backpressure problems.

Writing to CSV File​


const { stringify } = require("csv-stringify");
const fs = require("fs");

const stringifier = stringify({ header: true });
stringifier.pipe(fs.createWriteStream("output.csv"));

stringifier.write({ name: "Ali", age: 30 });
stringifier.end();
  • This code writes JSON data to CSV.

Generating CSV from Database​


db.each("SELECT * FROM users", (err, row) => {
  stringifier.write(row);
});
  • This method exports data without storing it in memory.

stream.pipeline For Large Files


const { pipeline } = require("stream/promises");

await pipeline(
  fs.createReadStream("input.csv"),
  parse({ columns: true }),
  stringify({ header: true }),
  fs.createWriteStream("output.csv")
);
  • This structure makes error management automatic.

CSV → JSON Conversion


fs.createReadStream("data.csv")
  .pipe(parse({ columns: true }))
  .pipe(JSONStream.stringify())
  .pipe(fs.createWriteStream("data.json"));
  • This method is suitable for large files.

JSON → CSV Conversion


Readable.from(jsonArray)
  .pipe(stringify({ header: true }))
  .pipe(fs.createWriteStream("out.csv"));
  • This code converts JSON string to CSV.
  1. Managing Inaccurate Data

  • Keep log with line number

  • Write the incorrect lines to a separate file

  • Do not stop the application

Frequently Asked Questions​

1. node-csv or fast-csv? node-csv offers a more flexible structure.

2. Does it block large files? No, it does not block if stream is used.

3. What should I do if the delimiter is different? delimiter: ";" Set like .

4. Can I read CSV without a library? Not recommended, edge-cases cause problems.

Result​

With node-csv, CSV files are processed securely and scalably. The Stream approach keeps memory usage to a minimum.

You can easily use this structure when processing high volumes of data on GenixNode.