Created: 2014-05-19 05:37
Updated: 2018-11-26 06:28
License: mit


A Lua parser and standard library targeting the Mozilla Parser API AST.


Generated and minified sources are available on NPM

npm install lua2js


  • Development: peg.js
  • Runtime: None =)


Many lua programs run unmodified on lua2js. See the lua-tests folder for some examples.

JavaScript <-> Lua

When the luaCalls option is on, the arguments to javascript functions will be adjusted in the following ways:

  • If the function was being called with : syntax, the variable that would be passed as self is used as this
  • If a LuaTable is passed as an argument if the table only has numeric entries, an array will be passed. If there are no numeric entire, a javascript object will be passed. If both are present, the LuaTable object will be passed.
  • If the last argument is a function that returned multiple values, they will be unpacked as normal.

Lua Syntax Not Supported (Yet)

  • Long form strings and comments will choke on internal ]]'s even when using the [==[ syntax.
  • The goto statement and labels from lua 5.2 are unimplemented.
  • The global environment doesn't exist in _ENV or _G.

Lua Runtime Standard Library

  • pairs ipairs next all work on both lua tables and javascript objects/arrays
  • MetaTable and operator overloading work on LuaTables

Lua Standard Library Holes

  • getmetatable and setmetatable only work on LuaTable's
  • requires and package interface tables are missing.
  • The debug library is missing.
  • The coroutine library is missing (and no runtime support for coroutines exists)`
  • The bit32 library from lua 5.2 is incomplete.
  • string.format is less powerful then the lua version.
  • Pattern matching (string.find, string.match, string.gsub) is unimplemented.
  • Code loading (load, dostring, dofile, etc...) is unimplemented.

Parser Options

Boolean Options

  • decorateLuaObjects: Mark lua functions so can call them differently. Also the {} syntax will create a LuaTable object instead of a normal javascript object.
  • encloseWithFunctions: Protect variable scoping by creating functions and calling them.
  • forceVar: Forbid generation of let statements to maintain ES5 compatibility.
  • loose: Try not to throw parse errors, and collect them in ast.errors instead.
  • luaCalls: Rewrite function calls to use to fix-up various lua<->javascript calling convention differences.
  • luaOperators: Use functions in the standard library instead of conventional operators to improve Lua compatibility. (e.g. a+b becomes __lua.add(a,b))
  • noSharedObjects: Make sure all AST nodes are unique objects. Can prevent bugs when performing transformations on the returned AST.
  • allowRegularFunctions: Normally all functions are emitted in something = function() { ... } format. Enable this to emit the more normal (but sometimes less compatible) function something() { ... }.


You can run a suite of tests using the npm test command. The tests require having nodeunit installed globally and a working Lua interpreter on your path. The tests fall into three categories.

  • Simple Tests: These are contained in an array toward the top of test.js and test simple lua programs without the Lua interpreter.
  • ./lua-tests/: A collection of various lua programs from around the internet. These are interpreted in node and their output compared against the systems lua interpreter.
  • ./lua-testmore/: Selected tests from the lua-TestMore project. Similar to the above.


Code and documentation copyright 2014 Rob Blanckaert. Code released under the MIT license.

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