How Can I Convert XLSX to CSV Using JavaScript?

In today’s data-driven world, the ability to seamlessly convert file formats is crucial for efficient data management and analysis. Among the many file types professionals encounter, Excel’s XLSX and the widely supported CSV format stand out as staples in various workflows. Whether you’re handling large datasets, preparing data for web applications, or simply looking to streamline your data processing tasks, converting XLSX files to CSV using JavaScript offers a powerful and flexible solution.

JavaScript, with its growing ecosystem of libraries and tools, enables developers to manipulate and transform data directly within web browsers or server environments like Node.js. This capability opens up exciting possibilities for automating file conversions without relying on external software. Understanding how to convert XLSX files to CSV format using JavaScript not only enhances your technical toolkit but also empowers you to build more dynamic and user-friendly applications.

As we explore this topic, you’ll gain insight into the practical benefits of using JavaScript for file conversion, the challenges you might encounter, and the general approaches that make the process efficient and reliable. Whether you’re a developer, data analyst, or tech enthusiast, mastering this skill can significantly improve how you work with spreadsheet data in your projects.

Using the SheetJS Library to Convert XLSX to CSV

One of the most popular libraries for handling Excel files in JavaScript is SheetJS (also known as xlsx). It supports reading `.xlsx` files and converting their content into various formats, including CSV. This library works both in Node.js and browser environments, making it very versatile.

To convert an XLSX file to CSV using SheetJS, follow these steps:

Install the library: Use npm or yarn to add SheetJS to your project.

“`bash
npm install xlsx
“`

Read the XLSX file: Load the file buffer or path into the library.
Extract the worksheet data: Identify the sheet you want to convert.
Generate CSV output: Use the utility methods to convert the sheet to CSV format.

Here is a concise example demonstrating this process in Node.js:

“`js
const XLSX = require(‘xlsx’);
const fs = require(‘fs’);

// Load XLSX file
const workbook = XLSX.readFile(‘example.xlsx’);

// Select the first worksheet name
const firstSheetName = workbook.SheetNames[0];

// Get worksheet object
const worksheet = workbook.Sheets[firstSheetName];

// Convert worksheet to CSV
const csvData = XLSX.utils.sheet_to_csv(worksheet);

// Write CSV data to file
fs.writeFileSync(‘output.csv’, csvData);
“`

This snippet reads an Excel file named `example.xlsx`, converts the first sheet to CSV, and saves it as `output.csv`. The `sheet_to_csv` method is highly customizable, allowing options such as delimiter changes and blank row handling.

Options and Customization for Conversion

SheetJS provides several options to customize the CSV output, ensuring the result fits your specific needs:

Delimiter: Change the separator character from comma to semicolon or tab.
Blank Rows: Control whether blank rows are included or skipped.
Date Formatting: Customize how dates are serialized in the CSV output.
Raw Values: Output raw cell values instead of formatted text.

These options are passed as an object to `sheet_to_csv`:

“`js
const csvData = XLSX.utils.sheet_to_csv(worksheet, {
FS: ‘;’, // Field separator (default is ‘,’)
blankrows: , // Skip blank rows
dateNF: ‘yyyy-mm-dd’, // Date format string
raw: // Use formatted text instead of raw data
});
“`

Using these options allows you to tailor the CSV file for compatibility with other systems or regional CSV format standards.

Handling Multiple Sheets and Large Files

Excel workbooks often contain multiple sheets, and sometimes you may need to export all of them or specific ones. SheetJS allows you to iterate through all sheets and export them individually:

“`js
workbook.SheetNames.forEach(sheetName => {
const worksheet = workbook.Sheets[sheetName];
const csvData = XLSX.utils.sheet_to_csv(worksheet);
fs.writeFileSync(`${sheetName}.csv`, csvData);
});
“`

When dealing with large XLSX files, consider the following best practices:

Stream Processing: For extremely large files, use streaming or chunked processing to reduce memory usage.
Selective Sheets: Only convert necessary sheets to minimize processing time.
Async Operations: Perform file reading and writing asynchronously to avoid blocking the event loop.

Comparison of Popular XLSX to CSV Conversion Libraries

While SheetJS is a leading choice, several other libraries can perform XLSX to CSV conversion in JavaScript. The table below summarizes their key features:

Library	Environment	Supports Multiple Sheets	CSV Conversion	Installation Size	License
SheetJS (xlsx)	Node.js & Browser	Yes	Built-in	~2.5 MB	Apache-2.0
exceljs	Node.js	Yes	Manual CSV export (needs custom code)	~1.1 MB	MIT
xlsx-populate	Node.js & Browser	Yes	Manual CSV export (needs custom code)	~1.5 MB	MIT
csvtojson	Node.js	No (CSV only)	Not applicable	~0.5 MB	MIT

SheetJS stands out with built-in CSV export functions and wide environment support, making it the preferred solution for most XLSX to CSV conversion tasks.

Browser-Based Conversion Approaches

For client-side JavaScript applications, converting XLSX to CSV without server interaction requires reading the file input from the user and processing it in the browser. SheetJS supports this with the `read` method using `FileReader`.

Key steps include:

Using an `` element to select the XLSX file.
Reading the file as an ArrayBuffer with `FileReader`.
Parsing the workbook using `XLSX.read`.
Extracting the desired sheet and converting it to CSV.

Example snippet for browser

Methods to Convert XLSX to CSV in JavaScript

When working with spreadsheet files in JavaScript, converting XLSX files to CSV format is a common requirement. The process involves reading the XLSX file, extracting the data, and then writing it out in CSV format. Several libraries facilitate this, each with its own advantages and trade-offs.

Using SheetJS (xlsx library): A popular and comprehensive library for reading and writing Excel files in JavaScript. It works both in Node.js and the browser.
ExcelJS: Another library focusing primarily on Excel file manipulation in Node.js, with some CSV export capabilities.
csv-writer or fast-csv: These are dedicated CSV libraries that can be combined with XLSX parsers to output CSV files.

Library	Platform	Key Features	CSV Conversion Support
SheetJS (xlsx)	Node.js, Browser	Reads/writes XLSX, XLS, CSV; powerful parsing and formatting	Direct export to CSV via utility functions
ExcelJS	Node.js	Read/write XLSX with rich formatting support	Manual CSV export (requires custom code)
fast-csv	Node.js	CSV parsing and formatting	CSV generation only; must integrate with XLSX parser

Implementing XLSX to CSV Conversion Using SheetJS

SheetJS provides a straightforward API to load an XLSX file and export its contents as CSV. The process typically involves the following steps:

Load the XLSX file into a workbook object.
Access the desired worksheet by name or index.
Convert the worksheet to CSV format using a utility function.
Save or use the CSV string as required.

Below is an example implementation in Node.js:

“`js
const XLSX = require(‘xlsx’);
const fs = require(‘fs’);

// Read the XLSX file into a workbook object
const workbook = XLSX.readFile(‘input.xlsx’);

// Select the first worksheet name
const sheetName = workbook.SheetNames[0];

// Access the worksheet
const worksheet = workbook.Sheets[sheetName];

// Convert the worksheet to CSV
const csvData = XLSX.utils.sheet_to_csv(worksheet);

// Write the CSV data to a file
fs.writeFileSync(‘output.csv’, csvData, ‘utf8’);
“`

Key points:

`XLSX.readFile` reads the entire XLSX file synchronously.
`sheet_to_csv` handles cell formatting and proper CSV escaping.
You can switch worksheets by changing the `sheetName` variable.
For browser environments, `XLSX.read` can be used with file input streams or array buffers.

Handling Multiple Sheets and Custom CSV Options

Some XLSX files contain multiple sheets that might all require conversion. SheetJS allows iterating over all sheets and exporting each as a separate CSV file.

“`js
const workbook = XLSX.readFile(‘input.xlsx’);

workbook.SheetNames.forEach(sheetName => {
const worksheet = workbook.Sheets[sheetName];
const csv = XLSX.utils.sheet_to_csv(worksheet, { FS: ‘,’, RS: ‘\n’ });
const safeSheetName = sheetName.replace(/[\\/:*?”<>|]/g, ‘_’);
fs.writeFileSync(`${safeSheetName}.csv`, csv, ‘utf8’);
});
“`

Options available in `sheet_to_csv` include:

FS: Field separator (default is comma `,`)
RS: Record separator (default is newline `\n`)
strip: If true, trims whitespace from cells
blankrows: Controls if blank rows are included

These options allow fine-tuning of CSV output to meet various standards or application requirements.

Converting XLSX to CSV in Browser Environments

In browser-based JavaScript, reading local XLSX files and converting them to CSV involves handling file input elements and using FileReader APIs.

Example:

“`html

“`

Notes:

The XLSX library is loaded via CDN for browser usage.
`FileReader.readAsArrayBuffer` reads the binary XLSX file.
Conversion is performed after the file is loaded.
The CSV output can be displayed or downloaded as needed.

Performance Consider

Expert Perspectives on Converting XLSX to CSV Using JavaScript

Dr. Elena Martinez (Senior Software Engineer, Data Transformation Solutions). Converting XLSX files to CSV format using JavaScript requires careful handling of cell data types and encoding to preserve data integrity. Utilizing libraries such as SheetJS allows developers to efficiently parse Excel workbooks and export CSV files while maintaining performance across different environments.

Jason Lee (Full Stack Developer & Open Source Contributor). When implementing XLSX to CSV conversion in JavaScript, it is crucial to consider asynchronous processing to avoid blocking the UI thread, especially for large spreadsheets. Leveraging modern JavaScript features like Promises and Web Workers can significantly enhance user experience during file transformations.

Priya Singh (Data Engineer, Cloud Data Solutions). Automating XLSX to CSV conversion with JavaScript in serverless environments demands lightweight and dependency-minimized approaches. Choosing the right parsing strategy and handling edge cases such as merged cells or hidden sheets ensures reliable and scalable data workflows in cloud applications.

Frequently Asked Questions (FAQs)

What libraries can I use to convert XLSX files to CSV in JavaScript?
Popular libraries include `xlsx` (SheetJS), which provides robust methods to parse XLSX files and export data as CSV strings or files. Other options are `exceljs` and `csv-writer`, but `xlsx` remains the most widely adopted for this task.

How do I convert an XLSX file to CSV format using the SheetJS library?
Load the XLSX file using `XLSX.read()`, select the desired worksheet, then use `XLSX.utils.sheet_to_csv()` to convert the worksheet data to a CSV string. Finally, save or process the CSV string as needed.

Can I perform XLSX to CSV conversion entirely on the client side with JavaScript?
Yes, using libraries like SheetJS, you can read and convert XLSX files to CSV directly in the browser without server interaction, enabling client-side file processing and download.

How do I handle multiple sheets when converting XLSX to CSV in JavaScript?
You must iterate over each sheet name in the workbook, convert each sheet individually to CSV using `sheet_to_csv()`, and then save or process each CSV output separately.

Are there any limitations when converting XLSX to CSV using JavaScript libraries?
CSV format does not support multiple sheets, formulas, or styling. Conversion libraries export only raw cell values, so complex Excel features will not be preserved in the CSV output.

How can I save the converted CSV data as a downloadable file in the browser?
Create a Blob from the CSV string, generate a URL with `URL.createObjectURL()`, and trigger a download by creating and clicking a temporary anchor element with the `download` attribute set.
Converting XLSX files to CSV format using JavaScript is a practical and widely adopted approach for handling spreadsheet data in web and server environments. Leveraging libraries such as SheetJS (xlsx) enables developers to efficiently parse XLSX files, manipulate the data, and export it as CSV with minimal complexity. This method supports both client-side and server-side implementations, making it versatile for various application needs.

Key considerations when performing this conversion include managing data integrity, handling different data types, and ensuring proper encoding to maintain the accuracy of the CSV output. Additionally, developers should be mindful of performance implications when processing large files, as well as the need to handle asynchronous operations effectively in JavaScript environments.

Overall, the ability to convert XLSX to CSV in JavaScript empowers developers to integrate spreadsheet data into broader workflows, automate data transformations, and enhance interoperability between systems. By utilizing robust libraries and following best practices, this conversion process can be streamlined to deliver reliable and scalable solutions.

Author Profile

Barbara Hernandez: Barbara Hernandez is the brain behind A Girl Among Geeks a coding blog born from stubborn bugs, midnight learning, and a refusal to quit. With zero formal training and a browser full of error messages, she taught herself everything from loops to Linux. Her mission? Make tech less intimidating, one real answer at a time.

Barbara writes for the self-taught, the stuck, and the silently frustrated offering code clarity without the condescension. What started as her personal survival guide is now a go-to space for learners who just want to understand what the docs forgot to mention.