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1.7.1 • Public • Published


A blazing fast 100% spec compliant, self-hosted javascript parser written in Typescript.

Seafox NPM GitHub license Total alerts Circle License


  • Conforms to the standard ECMAScript® 2021 (ECMA-262 11th Edition) language specification
  • Support for additional ECMAScript features for Web Browsers
  • Optionally track syntactic node locations
  • Emits an ESTree-compatible abstract syntax tree
  • Lexical analysis
  • No backtracking
  • Low memory usage
  • Insane performance both on desktop computers and handheld devices
  • Twice as fast as other Javascript parsers
  • Very well tested (~33 000 unit tests with full code coverage)
  • Lightweight - ~84 KB minified


npm install seafox --save-dev


Seafox generates AST according to ESTree AST format, and can be used to perform syntactic analysis (parsing) or lexical analysis (tokenization) of a JavaScript program, and with ES2015 and later a JavaScript program can be either a script or a module.

The parse method exposed by Seafox takes an optional options object which allows you to specify whether to parse in script mode (the default) or in module mode.

This is the available options:

  // Allow parsing using Module as the goal symbol
  module?: boolean;
  // The flag to enable start and end offsets and line/column location information to each node
  loc: false;
  // Disable web compatibility
  disableWebCompat: false;
  // The flag to attach raw property to each literal and identifier node
  raw: false;
  // Enabled directives
  directives: false;
  // The flag to allow return in the global scope
  globalReturn: false;
  // The flag to enable implied strict mode
  impliedStrict: false;
// Enable non-standard parenthesized expression node
  preserveParens: false;
   // Allows token extraction. Accepts only a function
  onToken: function() {}

Example usage:

import { parseScript, parseModule, parse } from './seafox';
parseScript('({x: [y] = 0} = 1)');
parseModule('({x: [y] = 0} = 1)', { directives: true, raw: true });
parse('({x: [y] = 0} = 1)', { module: true });
parse('({x: [y] = 0} = 1)');

Lexical analysis

Lexical analysis can only be done during parsing and accepts only a function type as the option

 parseScript('foo = bar', { onToken: () => {}});

The callback function have 4 arguments.

Arguments Description
token The token to be extracted
value Value of the extracted token
start Start position of the extracted token
end End position of the extracted token

The loc option needs to be enabled for start and end. Otherwise this values will be set to undefined


Seafox is developed for performance and low memory usage, and the parser is about 2x - 4x faster than all other javascript parsers.


npm i seafox

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  • kendon
  • nicolo-ribaudo