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0.3.1 • Public • Published


A Lua parser written in JavaScript, originally written by Oskar Schöldström for his bachelor's thesis at Arcada.


Install through npm install luaparse.



var parser = require('luaparse');
var ast = parser.parse('i = 0');


require(['luaparse'], function(parser) {
  var ast = parser.parse('i = 0');


<script src="luaparse.js"></script>
var ast = luaparse.parse('i = 0');

Parser Interface

Basic usage:

luaparse.parse(code, options);

The output of the parser is an Abstract Syntax Tree (AST) formatted in JSON.

The available options are:

  • wait: false Explicitly tell the parser when the input ends.
  • comments: true Store comments as an array in the chunk object.
  • scope: false Track identifier scopes.
  • locations: false Store location information on each syntax node.
  • ranges: false Store the start and end character locations on each syntax node.
  • onCreateNode: null A callback which will be invoked when a syntax node has been completed. The node which has been created will be passed as the only parameter.
  • onCreateScope: null A callback which will be invoked when a new scope is created.
  • onDestroyScope: null A callback which will be invoked when the current scope is destroyed.
  • onLocalDeclaration: null A callback which will be invoked when a local variable is declared. The identifier will be passed as the only parameter.
  • luaVersion: '5.1' The version of Lua the parser will target; supported values are '5.1', '5.2', '5.3' and 'LuaJIT'.
  • extendedIdentifiers: false Whether to allow code points ≥ U+0080 in identifiers, like LuaJIT does. Note: setting luaVersion: 'LuaJIT' currently does not enable this option; this may change in the future.
  • encodingMode: 'none' Defines the relation between code points ≥ U+0080 appearing in parser input and raw bytes in source code, and how Lua escape sequences in JavaScript strings should be interpreted. See the Encoding modes section below for more information.

The default options are also exposed through luaparse.defaultOptions where they can be overriden globally.

There is a second interface which might be preferable when using the wait option.

var parser = luaparse.parse({ wait: true });
parser.write('foo = "');
var ast = parser.end('"');

This would be identical to:

var ast = luaparse.parse('foo = "bar"');

AST format

If the following code is executed:

luaparse.parse('foo = "bar"');

then the returned value will be:

  "type": "Chunk",
  "body": [
      "type": "AssignmentStatement",
      "variables": [
          "type": "Identifier",
          "name": "foo"
      "init": [
          "type": "StringLiteral",
          "value": "bar",
          "raw": "\"bar\""
  "comments": []

Encoding modes

Unlike strings in JavaScript, Lua strings are not Unicode strings, but bytestrings (sequences of 8-bit values); likewise, implementations of Lua parse the source code as a sequence of octets. However, the input to this parser is a JavaScript string, i.e. a sequence of 16-bit code units (not necessarily well-formed UTF-16). This poses a problem of how those code units should be interpreted, particularly if they are outside the Basic Latin block ('ASCII').

The encodingMode option specifies how these issues should be handled. Possible values are as follows:

  • 'none': Source code characters all pass through as-is and string literals are not interpreted at all; the string literal nodes contain the value null. This is the default mode.
  • 'x-user-defined': Source code has been decoded with the WHATWG x-user-defined encoding; escapes of bytes in the range [0x80, 0xff] are mapped to the Unicode range [U+F780, U+F7FF].
  • 'pseudo-latin1': Source code has been decoded with the IANA iso-8859-1 encoding; escapes of bytes in the range [0x80, 0xff] are mapped to Unicode range [U+0080, U+00FF]. Note that this is not the same as how WHATWG standards define the iso-8859-1 encoding, which is to say, as a synonym of windows-1252.

Custom AST

The default AST structure is somewhat inspired by the Mozilla Parser API but can easily be overriden to customize the structure or to inject custom logic.

luaparse.ast is an object containing all functions used to create the AST, if you for example wanted to trigger an event on node creations you could use the following:

var luaparse = require('luaparse'),
    events = new (require('events').EventEmitter);

Object.keys(luaparse.ast).forEach(function(type) {
  var original = luaparse.ast[type];
  luaparse.ast[type] = function() {
    var node = original.apply(null, arguments);
    events.emit(node.type, node);
    return node;
events.on('Identifier', function(node) { console.log(node); });
luaparse.parse('i = "foo"');

this is only an example to illustrate what is possible and this particular example might not suit your needs as the end location of the node has not been determined yet. If you desire events you should use the onCreateNode callback instead).


The lexer used by luaparse can be used independently of the recursive descent parser. The lex function is exposed as luaparse.lex() and it will return the next token up until EOF is reached.

Each token consists of:

  • type expressed as an enum flag which can be matched with luaparse.tokenTypes.
  • value
  • line, lineStart
  • range can be used to slice out raw values, eg. foo = "bar" will return a StringLiteral token with the value bar. Slicing out the range on the other hand will return "bar".
var parser = luaparse.parse('foo = "bar"', { wait: true });
parser.lex(); // { type: 8, value: "foo", line: 1, lineStart: 0, range: [0, 3] }
parser.lex(); // { type: 32, value: "=", line: 1, lineStart: 0, range: [4, 5]}
parser.lex(); // { type: 2, value: "bar", line: 1, lineStart: 0, range: [6, 11] }
parser.lex(); // { type: 1, value: "<eof>", line: 1, lineStart: 0, range: [11 11] }
parser.lex(); // { type: 1, value: "<eof>", line: 1, lineStart: 0, range: [11 11] }


Have a look in the examples directory of the repository for some code examples or check them out live.


The luaparse executable can be used in your shell by installing luaparse globally using npm:

$ npm install -g luaparse
$ luaparse --help

Usage: luaparse [option]... [file|code]...

  -c|--code [code]   parse code snippet
  -f|--file [file]   parse from file
  -b|--beautify      output an indenteted AST
  --[no]-comments    store comments. defaults to true
  --[no]-scope       store variable scope. defaults to false
  --[no]-locations   store location data on syntax nodes. defaults to false
  --[no]-ranges      store start and end character locations. defaults to false
  -q|--quiet         suppress output

  luaparse --no-comments -c "locale foo = \"bar\""
  luaparse foo.lua bar.lua

Example usage

$ luaparse "i = 0"



Has been tested in at least IE6+, Firefox 3+, Safari 4+, Chrome 10+, Opera 10+, Node 0.4.0+, RingoJS 0.8-0.9, Rhino 1.7R4-1.7R5, Nashorn 1.8.0.

Quality Assurance

TL;DR simply run make qa. This will run all quality assurance scripts but assumes you have it set up correctly.

Begin by cloning the repository and installing the development dependencies with npm install.

The luaparse test suite uses testem as a test runner, and because of this it's very easy to run the tests using different javascript engines or even on locally installed browsers.

Test runners

  • make test uses node.
  • make testem-engines uses node, ringo and rhino 1.7R5. This requires that you have the engines installed.
  • make test-node uses a custom command line reporter to make the output easier on the eyes while practicing TDD.
  • By installing testem globally you can also run the tests in a locally installed browser.

Other quality assurance measures

  • You can check the function complexity using complexity-report using make complexity-analysis
  • Running make coverage will generate the coverage report. To simply check that all code has coverage you can run make coverage-analysis.
  • make lint, make benchmark, make profile.


By running make docs all documentation will be generated.

Projects using/extending luaparse

  • luamin, a Lua minifier written by Mathias Bynens.
  • Ace, an online code editor.


  • Initial tests are scaffolded from yueliang and then manually checked for error.
  • Much of the code is based on LuaMinify, the Lua source and Esprima. All awesome projects.





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