How to Handle CSV, Excel, and JSON Uploads in Node.js (Without Losing Your Mind)

Ever found yourself trying to build a feature for users to upload files, and suddenly you're knee-deep in weird CSV quirks, Excel formats, and complex JSON structures?
I’ve been there too. Here’s a simple guide to help you handle file uploads in Node.js without losing your mind.

Step 1: Accept File Uploads (With Multer)

First, use multer to accept file uploads in Express:

npm install multer

Basic setup:

const express = require('express');
const multer = require('multer');
const upload = multer({ dest: 'uploads/' });
const app = express();

app.post('/upload', upload.single('file'), (req, res) => {
  console.log(req.file);
  res.send('File uploaded!');
});

Step 2: Parse Different File Types

1. CSV Files

Use csv-parser:

npm install csv-parser

Code:

const fs = require('fs');
const csv = require('csv-parser');

fs.createReadStream('uploads/file.csv')
  .pipe(csv())
  .on('data', (row) => {
    console.log(row);
  });

2.Excel Files

Excel Files

npm install xlsx

Code:

const xlsx = require('xlsx');

const workbook = xlsx.readFile('uploads/file.xlsx');
const sheetName = workbook.SheetNames[0];
const data = xlsx.utils.sheet_to_json(workbook.Sheets[sheetName]);

console.log(data);

3.JSON Files

Simple:

const fs = require('fs');

const data = JSON.parse(fs.readFileSync('uploads/file.json', 'utf8'));
console.log(data);

Step 3: Handle Common Data Issues

• Normalize date formats (e.g., with dayjs)
• Remove empty rows
• Deduplicate entries
• Validate column headers

Example (normalize phone numbers):

function cleanPhoneNumber(num) {
  return num.replace(/\D/g, '');
}

Step 4: Structure Your Code

• Create a separate module for each file type
• Keep upload logic separate from parsing
• Log errors clearly

Final Thoughts

Handling messy files is something you’ll encounter while creating real-world apps. But don’t worry! With the right tools, you can easily work with CSV, Excel, and JSON files without losing your mind.

Got your own tips or tools? Drop them in the comments!