Parser for JavaScript

This package is not currently in any snapshots. If you're interested in using it, we recommend adding it to Stackage Nightly. Doing so will make builds more reliable, and allow to host generated Haddocks.

BSD-3-Clause licensed by Alan Zimmerman
Maintained by Erik de Castro Lopo

Parser for JavaScript

Build Status

Based (loosely) on language-python

Two Versions

There are currently two versions:

  • 0.5 series : Is a continuation of the 0.5.X.Y series, from the [master] ( branch of this github repository.

  • 0.6 and 0.7 series : This has a vastly different and improved AST which makes if far more difficult to build an non-sensical Javascript AST. This code is in the new-ast branch of this github repository.

How to build

Make sure your locale supports UTF-8. For example, on most Unix-like platforms, you can type:

export LC_ALL=en_US.UTF-8


cabal clean && cabal configure && cabal build


cabal clean && cabal configure -fbuildtests && cabal build

Running the tests


To debug the grammar

happy -iparse.txt -g -a  -d src/Language/JavaScript/Parser/Grammar5.y

This generates src/Language/JavaScript/Parser/Grammar5.hs, delete this when done with the debug version

UTF8/Unicode version

Alex 3.0 now supports unicode natively, and has been included as a dependency in the cabal file.

Note: The generation of the lexical analyser has been separated out, to remove the install-time dependency on Alex. If any changes need to be made to the lexer, the Lexer.x source lies in src-dev, and the script will invoke Alex with the appropriate directories.


ChangeLog for language-javascript – 2020-03-22

  • Add support for async function specifiers and await keyword. – 2019-10-10

  • Add support for (Ryan Hendrickson):
    • Destructuring in var declarations
    • const in for statements
    • ES6 property shorthand syntax
    • Template literals
    • Computed property names
    • Bare import declarations
    • Exotic parameter syntaxes
    • Generators and yield
    • Method definitions
    • classes - super keyword – 2019-06-17

  • Add support for (Cyril Sobierajewicz):
    • Unparenthesized arrow functions of one parameter
    • Export from declarations
    • Add back support for identifiers named as – 2019-05-03

  • Add support for for..of and friends (Franco Bulgarelli)