BSD-3-Clause licensed by Alan Zimmerman
Maintained by Erik de Castro Lopo
This version can be pinned in stack with:language-javascript-,3865

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)