# ExcelJS — Read, Write, and Stream Excel Spreadsheets in Node.js

> A full-featured library for creating, reading, and manipulating XLSX and CSV files in Node.js with streaming support for large datasets.

## Install

Save as a script file and run:

# ExcelJS — Read, Write, and Stream Excel Spreadsheets in Node.js

## Quick Use
```bash
npm install exceljs
```
```js
const ExcelJS = require('exceljs');
const workbook = new ExcelJS.Workbook();
const sheet = workbook.addWorksheet('Report');
sheet.addRow(['Name', 'Score']);
sheet.addRow(['Alice', 95]);
await workbook.xlsx.writeFile('report.xlsx');
```

## Introduction
ExcelJS provides a complete API for generating and parsing Excel files in Node.js without requiring Microsoft Office. It supports rich formatting, formulas, images, charts metadata, and streaming — making it suitable for server-side report generation and ETL pipelines that handle millions of rows.

## What ExcelJS Does
- Creates XLSX workbooks with multiple sheets, cell styles, merged cells, and conditional formatting
- Reads existing XLSX files preserving formulas, data validations, and defined names
- Streams rows to disk or HTTP responses for memory-efficient export of large datasets
- Supports CSV reading and writing with configurable delimiters and encoding
- Handles rich cell types including dates, hyperlinks, rich text, and images

## Architecture Overview
ExcelJS models workbooks as in-memory object graphs of worksheets, rows, and cells. The XLSX serializer uses a streaming XML writer (SAX-style) that flushes sheet data in chunks, preventing memory exhaustion on large exports. For reading, it provides both a full-parse mode (entire workbook in memory) and a streaming reader that emits row events, suitable for processing files that exceed available RAM.

## Self-Hosting & Configuration
- Install from npm — pure JavaScript, no native bindings required
- Use `workbook.xlsx.writeFile(path)` for disk output or `workbook.xlsx.write(stream)` for HTTP responses
- Enable streaming writes via `new ExcelJS.stream.xlsx.WorkbookWriter({ stream })` for constant-memory exports
- Configure default column widths, row heights, and page setup (orientation, margins) per worksheet
- Set number formats, fonts, borders, and fills at the cell or column level

## Key Features
- Streaming writer keeps memory flat regardless of row count — tested with 1M+ rows
- Full style support: fonts, fills, borders, alignment, number formats, and conditional formatting
- Data validation rules (dropdowns, numeric ranges) embedded directly in cells
- Auto-filter and freeze-pane support for user-friendly spreadsheets
- Over 15,000 GitHub stars and 4 million weekly npm downloads

## Comparison with Similar Tools
- **SheetJS (xlsx)** — broader format support (XLS, ODS); ExcelJS offers richer styling and streaming writes
- **openpyxl (Python)** — Python equivalent; ExcelJS is the Node.js counterpart with similar capabilities
- **Apache POI (Java)** — enterprise-grade but JVM-only; ExcelJS runs anywhere Node.js does
- **csv-parser** — CSV-only streaming reader; ExcelJS handles both XLSX and CSV in one library
- **json2csv** — converts JSON to CSV; ExcelJS produces formatted Excel files with charts and styles

## FAQ
**Q: Can ExcelJS handle files with 100K+ rows?**
A: Yes. Use the streaming WorkbookWriter for writing and the streaming reader for parsing to maintain constant memory usage.

**Q: Does it support Excel formulas?**
A: Yes. You can set formula strings on cells. Results are calculated by Excel when the file is opened, not by ExcelJS itself.

**Q: Can I add images to spreadsheets?**
A: Yes. Use `worksheet.addImage()` with a buffer or file path. Supported formats include PNG, JPEG, and GIF.

**Q: Is it compatible with LibreOffice and Google Sheets?**
A: The generated XLSX files conform to the Open XML standard and open correctly in LibreOffice Calc and Google Sheets.

## Sources
- https://github.com/exceljs/exceljs
- https://github.com/exceljs/exceljs/blob/master/README.md

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Source: https://tokrepo.com/en/workflows/asset-cc9ce2fb
Author: Script Depot