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The flow-parser package

This package contains the Flow parser in its compiled-to-JavaScript form.

What is Flow

See The code for the Flow parser lives on GitHub.

What is the Flow Parser

The Flow Parser is a JavaScript parser written in OCaml. It produces an AST that conforms to the ESTree spec and that mostly matches what esprima produces. The Flow Parser can be compiled to native code or can be compiled to JavaScript using js_of_ocaml. This npm package contains the Flow parser compiled to JavaScript.


You can use the Flow parser in your browser or in node. To use in node you can just do

require('flow-parser').parse('1+1', {});

To use in the browser, you can add

<script src="flow_parser.js"></script>

which will make the flow object available to use like so:

flow.parse('1+1', {});


The second argument to flow.parse is the options object. Currently supported options:

  • esproposal_decorators (boolean, default false) - enable parsing of decorators
  • esproposal_class_instance_fields (boolean, default false) - enable parsing of class instance fields
  • esproposal_class_static_fields (boolean, default false) - enable parsing of class static fields
  • esproposal_export_star_as (boolean, default false) - enable parsing of export * as syntax
  • types (boolean, default true) - enable parsing of Flow types

bin scripts

  • flowparse - Pass it a string to parse or a file to parse and it dumps the AST to stdout
  • flowvalidate - Pass it one or more files and it checks if they parse