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Jasy - JavaScript Tooling Framework

Jasy is a collection of tools for dealing with JavaScript source code. It is based on Python3 and relies on a stable parser engine based on Narcissus/Spidermonkey by Mozilla.

The main goal of Jasy is to offer an API which could be used by developers to write their custom build/deployment scripts. Jasy offers an rich Python3-API. Your build script is just a normal Python script which includes the Jasy-API and defines so-called tasks.

Jasy also offers standalone tools for dealing with single JavaScript files to e.g. compress or format them.


Jasy is licensed under a dual license MIT + Apache V2. See separate license files for details. The parser implementation is under a triple open source license MPL 1.1/GPL 2.0/LGPL 2.1 as these are from the original Spidermonkey code.


  • Full JavaScript 1.8 parser based on Narcissus (which itself is based on Spidermonkey)
  • Reworked parser for better child handling (easier to traverse tree compared to original)
  • Full support for JavaScript 1.8 (Generators, Block Scope, Function Expressions, Array Comprehensions, ...)
  • Comment processing (Comments are attached to nodes and are part of the AST)

Project Handling

  • Project Support (Bundling multiple projects)
  • Build scripts are plain Python and can do everything you want to do. No limitations.
  • Import Jasy and define your own tasks (using Python decorator "task") (See demo/ as an example)

Dependency Analysis

  • Dependency Analysis (with support for permutations).
  • All dependencies are regarded as load-time specific.
  • Automatic and fine-tunable breaking of circular dependencies.
  • Detects all objects which are not declared in the file itself e.g. window, document, my.namespaced.Class, etc.

Dead Code Removal

  • Resolves conditions and removes blocks which could not be reached
  • Function part of the permutation support
  • Supports switch statements
  • Supports conditional statements (?:)
  • Resolves boolean, number and string compares
  • Supports AND and OR operators

Permutation Features

  • Permutation Support (building different results from one code base)
  • Might be used to remove debug blocks or alternative code

Compression Features

  • Comment Removal
  • White Space Removal (even in some quirky places e.g. keywords before strings, etc.)

Optimizer Features

  • Renames local variables/functions/exceptions (based on their usage number)
  • Renames file private variables (starting with double underscore by convention)
  • Combines multi var statements into one per function (really all of them)
  • Removes needless blocks (with just one statement)
  • Automatically combines strings and numbers (e.g. "Version " + 1.3 => "Version 1.3")
  • Optimizes if(-else) statements with expressions as content
    • Translates if-statements without else using && or || operators
    • Translates if-statements with else using conditional operator ? : (especially worth with returns/assignments)
  • Removes needless else (if previous if-block ends with a return/throw statement)
  • Removes needless parens based on priority analysis on the AST

Developer Support

  • Generates a so-named "source" version which loads the original class files which is useful during the development phase of an application.

Localization Features

  • Unicode CLDR Data Transformation
    • Rebuilds XML files to nicely useable ultra-modular JSON data classes
    • Integrates with dependency system
    • Fast access to data without additional API possible
    • Supports project fallback chain
  • PO-File translations
    • Loads translations from PO-files
    • Create language specific variants
    • Replaces string instances directly inside the original file
    • Removes overhead through translation as no function call is needed anymore
    • Optimizes template replacement e.g. via %1 into a string "plus" operation


  • Auto Closure Wrapping for string optimizations, keyword optimization, etc.
  • String optimizations
  • API data
  • Code Quality Checks (Lint)
  • Pretty Printer
  • ...