modern-xlsx

High-performance XLSX read/write for JavaScript & TypeScript, powered by Rust + WASM.

API Docs · Wiki · Feature Comparison · Examples · Changelog · Playground

---

Full cell styling, data validation, conditional formatting, frozen panes, hyperlinks, comments, sheet protection, and more — features that SheetJS locks behind a paid Pro license — all free and open source.

import { initWasm, Workbook } from 'modern-xlsx';

await initWasm();

const wb = new Workbook();
const ws = wb.addSheet('Sheet1');
ws.cell('A1').value = 'Hello';
ws.cell('B1').value = 42;

const bold = wb.createStyle().font({ bold: true }).build(wb.styles);
ws.cell('A1').styleIndex = bold;

await wb.toFile('output.xlsx');

Performance

Node.js 26, single thread, vs SheetJS (xlsx 0.20.3) — indicative, hardware-dependent:

Operation	modern-xlsx	SheetJS CE
Read (100K rows)	494 ms	2,072 ms	4.2x faster
Read (10K rows)	52 ms	177 ms	3.4x faster
Write (10K rows)	180 ms	159 ms	~parity
Output size (100K rows)	~5 MB	~40 MB	~8x smaller

The biggest wins are read speed (3-4x) and file size (~8x smaller); write throughput and CSV/JSON export are roughly at parity.

Browser bundle ~78 KB minified (~24 KB gzip) + ~1.9 MB WASM (~650 KB gzip). Zero runtime dependencies.

Install

npm install modern-xlsx

Note

Full API documentation lives in packages/modern-xlsx/README.md (the npm package README) and the project wiki.

Repository Structure

crates/
  modern-xlsx-core/       Rust core — OOXML parsing, XML generation, ZIP I/O
  modern-xlsx-wasm/       WASM bridge — wasm-bindgen exports

packages/
  modern-xlsx/            npm package — TypeScript API, tests, benchmarks

Architecture

flowchart TD
    TS["<b>TypeScript API</b><br/>Workbook · Worksheet · Cell<br/>StyleBuilder · ChartBuilder · utilities"]
    WASM["<b>WASM boundary</b><br/>wasm-bindgen bridge"]
    RUST["<b>Rust core</b><br/>OOXML parser &amp; writer<br/>(quick-xml SAX + zip)"]

    TS -- "JSON string" --> WASM
    WASM --> RUST
    RUST --> WASM
    WASM -- "JSON.parse" --> TS

Loading

Data crosses the WASM boundary as JSON strings for maximum throughput. The Rust core handles ZIP compression, SAX-style XML parsing, shared string table construction, and style resolution.

Development

# Rust tests (441 tests)
cargo test -p modern-xlsx-core

# WASM build
cd crates/modern-xlsx-wasm && wasm-pack build --target web --release \
  --out-dir ../../packages/modern-xlsx/wasm --no-opt

# TypeScript build + tests (1290 tests)
pnpm -C packages/modern-xlsx build
pnpm -C packages/modern-xlsx test

# Lint
cargo clippy -p modern-xlsx-core -- -D warnings
pnpm -C packages/modern-xlsx lint

Toolchain: Rust 1.96 MSRV / beta channel toolchain, currently 1.99 (Edition 2024) / TypeScript 7.0 / Vitest 5 / pnpm 12 / Biome 2.5

License

MIT