SheetJS — Read and Write Spreadsheets from JavaScript

Introduction

SheetJS (also published as the xlsx npm package) provides a pure-JavaScript engine for reading, editing, and writing spreadsheet data. It handles dozens of file formats—XLS, XLSX, CSV, ODS, and more—without native dependencies, making it suitable for both server-side Node.js scripts and in-browser applications.

What SheetJS Does

• Parses Excel files (XLS, XLSX, XLSB) into a uniform workbook object model
• Writes workbooks back to XLSX, CSV, HTML, JSON, and other output formats
• Runs in the browser with no server round-trips, enabling client-side export
• Converts between row-major arrays, JSON arrays, and HTML tables
• Handles multi-sheet workbooks, merged cells, number formats, and date parsing

Architecture Overview

SheetJS exposes a workbook/sheet data model. File bytes are fed to a format-specific parser that produces a workbook object containing named sheets. Each sheet is a sparse two-dimensional map of cell objects keyed by A1-style references. Utility functions convert between this internal representation and developer-friendly structures like arrays of objects. Writers serialize the workbook back into the target binary or text format.

Setup & Configuration

• Install from npm: npm install xlsx or load via CDN for browser use
• Import with require('xlsx') (CJS) or import * as XLSX from 'xlsx' (ESM)
• No native add-ons or external binaries required
• Use the streaming API (XLSX.stream) for large files that exceed memory limits
• Configure date handling with cellDates: true in the parsing options

Key Features

• Supports 20+ spreadsheet formats including legacy XLS and modern XLSB
• Zero native dependencies—runs identically in Node.js, Deno, and browsers
• Streaming reader and writer for processing large files efficiently
• Rich cell metadata including types, styles, formulas, and comments
• Active maintenance with frequent releases since 2012

Comparison with Similar Tools

• ExcelJS — provides deeper style and image support but only handles XLSX; SheetJS covers far more formats
• Papa Parse — CSV-only parser; SheetJS handles CSV plus binary Excel and ODS
• openpyxl (Python) — Python equivalent for XLSX; SheetJS brings the same capability to JavaScript
• Tabulator — focuses on UI table rendering; SheetJS focuses on file I/O

FAQ

Q: Can SheetJS run in the browser without a server? A: Yes. It parses files entirely in the browser using the File API or drag-and-drop input.

Q: Does SheetJS support writing styled XLSX files? A: The community edition handles data and basic number formats. The Pro edition adds full styling, images, and pivot tables.

Q: How does SheetJS handle large files? A: Use the streaming API to process rows incrementally rather than loading the entire workbook into memory.

Q: Is SheetJS free and open source? A: The core library is released under the Apache-2.0 license. An optional Pro tier adds advanced features.

Sources

• https://github.com/SheetJS/sheetjs
• https://docs.sheetjs.com/