sql.js — Run SQLite in the Browser with WebAssembly

Introduction

sql.js is SQLite compiled to WebAssembly via Emscripten. It gives you a complete, standards-compliant SQL database that runs entirely in the browser or in Node.js without any native dependencies. This is useful for client-side data processing, offline apps, and interactive SQL playgrounds.

What sql.js Does

• Provides a full SQLite engine compiled to WebAssembly
• Executes standard SQL queries including joins, indexes, and triggers
• Opens and exports .sqlite / .db files as binary arrays
• Runs in browsers, Node.js, Deno, and web workers
• Requires no server, native bindings, or build toolchain

Architecture Overview

sql.js uses Emscripten to compile the official SQLite C source into a WASM binary. The JavaScript wrapper loads this binary and provides a synchronous API that mirrors the SQLite C interface. The database lives in a WASM linear memory buffer. You can import an existing database from a Uint8Array and export it back for persistence.

Self-Hosting & Configuration

• Install via npm or load the WASM binary from a CDN
• Initialize with initSqlJs() which fetches and compiles the WASM module
• Pass locateFile to customize where the WASM binary is loaded from
• For persistence, export the database to a Uint8Array and save it to IndexedDB, localStorage, or a file
• Run heavy queries in a Web Worker to avoid blocking the main thread

Key Features

• Full SQLite feature set including FTS5, JSON1, and R-Tree extensions
• No native dependencies — works anywhere JavaScript runs
• Import and export .sqlite files as binary arrays
• Synchronous API makes sequential SQL operations straightforward
• WASM binary is under 1 MB gzipped

Comparison with Similar Tools

• Dexie.js — IndexedDB wrapper with a NoSQL-style API; sql.js provides full SQL
• PGlite — embedded Postgres in WASM; sql.js uses SQLite which is lighter
• better-sqlite3 — native Node.js binding; sql.js works in browsers without native code
• absurd-sql — persistence layer on top of sql.js using IndexedDB as a VFS

FAQ

Q: Is data persisted across page reloads? A: Not automatically. The database lives in memory. Export it to IndexedDB or the Origin Private File System for persistence.

Q: How large of a database can sql.js handle? A: It depends on available WASM memory. Databases of tens of megabytes work well; for larger datasets, consider a server-side database.

Q: Can I use existing .sqlite files? A: Yes. Pass the file as a Uint8Array to the Database constructor to open it.

Q: Is sql.js slower than native SQLite? A: WASM adds some overhead, but for typical workloads the difference is small. CPU-intensive queries on large tables will be noticeably slower.

Sources

• https://github.com/sql-js/sql.js
• https://sql.js.org