Flow JavaScript Parser

The flow-parser package provides a JavaScript parser, originally written in OCaml and compiled to JavaScript. It is designed to produce an Abstract Syntax Tree (AST) that largely conforms to the ESTree specification, similar to parsers like Esprima. This package is specifically built to understand and parse Flow's type annotations, making it a crucial component for tools that process Flow-typed code. As of April 2026, the current stable version is `0.309.0`, with releases appearing to follow a regular, often monthly or bi-monthly, cadence. Its key differentiator lies in its deep integration with the Flow type system and its ability to parse advanced Flow-specific syntax, while still outputting a widely compatible ESTree AST. It runs in both Node.js environments (requiring Node.js >= 0.4.0) and web browsers through a script tag.