lz-string

lz-string is a lightweight JavaScript/TypeScript implementation of an LZ-based compression algorithm purpose-built for compressing strings, not files. Version 2 ships as a joint CommonJS/ESM package with a bundled CLI, and offers multiple output encodings (base64, UTF-16, URI-component-safe, raw, Uint8Array) so compressed data can be safely stored wherever plain strings are expected.

It is one of the most widely used compression utilities in the JS ecosystem for shrinking data before writing to localStorage, embedding in URLs, or shipping over constrained network payloads, and has been ported to numerous other languages for cross-platform compatibility.

What You Get

• Core compress()/decompress() functions for raw string compression
• Encoding-specific helpers: base64, UTF-16, URI-component-safe, and Uint8Array output formats
• A CLI (lz-string binary) for compressing/decompressing files from the command line
• Dual CommonJS/ESM build output with TypeScript type definitions
• Zero runtime dependencies, keeping bundle size minimal for browser use

Common Use Cases

• Compressing large JSON or state blobs before storing them in browser localStorage/sessionStorage
• Shrinking data to fit within URL length limits by compressing to a URI-component-safe encoding
• Reducing payload size for data embedded in query strings or QR codes
• Cross-language data interchange using one of the library’s many community ports (Java, Python, Go, etc.)

Under The Hood

Architecture The library centers on a shared LZ78-style compression core split across _compress.ts and _decompress.ts, with index.ts acting as a thin dispatcher that wires the core engine to encoding-specific wrappers (base64, UTF-16, URI-component, raw, Uint8Array) found in their own subdirectories; a separate cli.ts built on commander exposes the same engine as a standalone binary for file-based compression, and node.ts provides Node-specific entry adjustments. Tech Stack Written in TypeScript, built with Vite (vite.config.mts for the library, a second config for the CLI) producing dual CJS/ESM output plus .d.ts type declarations via vite-plugin-dts; the package has zero runtime dependencies, keeping the compiled bundle minimal for browser consumption. Code Quality Tests live under src/__tests__ with accompanying __snapshots__, run via Vitest with coverage and benchmark modes (test:bench, test:coverage) configured in package.json; the recent v2 rewrite (joint CJS/ESM layout) suggests active modernization even though day-to-day commit activity is currently low. API Design The API is deliberately minimal — a handful of compress*/decompress* function pairs named after their target encoding — which makes the library trivial to adopt with almost no boilerplate, though the multiple encoding variants (base64 vs UTF-16 vs raw) require the caller to understand which encoding matches their storage target to avoid corruption.