lark-js

What it is and what it does

Lark-js is a Python package that acts as a command-line compiler for Lark grammars, converting `.lark` grammar files into standalone Javascript parsers. It is a port of the Lark parsing toolkit from Python to Javascript, using LALR(1) parsing to guarantee linear-time performance. The generated parsers build parse trees automatically and work in both Node.js and browsers.

The package is primarily a build tool: you install it on Python, write or reuse a Lark grammar file (which is language-agnostic EBNF), and run the `lark-js` command to produce a ready-to-use Javascript parser. The grammar syntax is portable across Python, Javascript, and Julia implementations of Lark, so you can share grammar definitions across projects in different languages.

Use it for:

• Generate a Javascript parser from an existing Lark grammar to embed parsing logic in a web application or Node.js service
• Port a Python project that uses Lark to Javascript while reusing the same grammar file unchanged
• Build a domain-specific language (DSL) parser in Javascript without hand-coding the parser logic
• Create interactive parsing tools or IDE-like features in the browser using Lark's step-by-step parsing capability

Worth the install?

AI-flagged interpretation of the facts on this page — verify before relying

Lark-js is a command-line tool that generates standalone LALR(1) parsers in Javascript from Lark grammar files, enabling portable grammar-based parsing across Python, Javascript, and Julia.

Yes, if you need to generate a Javascript parser from a Lark grammar and are comfortable with a dormant package. The tool is stable (Beta status, no known vulnerabilities), has low install friction, and solves a specific problem well. The 1551-day gap since last release is a concern for long-term maintenance, but the repository is not archived and the transpilation approach means it inherits Lark's stability. Install only if you actively need grammar-based parsing in Javascript.

Install

lark-js on PyPI

pip install lark-js

uv add lark-js

poetry add lark-js

Installing lark-js

Before you install

Low install friction with a single pure-Python dependency. The package is dormant (last release 2022-05-16, 1551 days ago) but the repository remains active and unarchived; maintenance is minimal but not abandoned.

License in practice

MIT license is permissive; you can use, modify, and distribute this package with minimal restrictions, provided you retain the license notice.

Quickstart

pip install lark-js
lark-js my_grammar.lark -o my_parser.js

Verify before relying

• Whether the transpiled Javascript output remains compatible with current Node.js and browser environments
• Current state of the 98% auto-transpilation claim and whether Python-side Lark updates actually sync to this package

Package facts

Evidence: Lark_js-0.1.4-py2.py3-none-any.whl

Tags

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