GitHub - xjslang/xjs: eXtensible JavaScript parser

| [.githooks](https://github.com/xjslang/xjs/tree/main/.githooks ".githooks") | [.githooks](https://github.com/xjslang/xjs/tree/main/.githooks ".githooks") | [feat(lexer): create token.RegisterType function](https://github.com/xjslang/xjs/commit/cf11a1d8795a15614fd8062b6c45912104ae26af "feat(lexer): create token.RegisterType function") | Apr 24, 2026 |

| [.github](https://github.com/xjslang/xjs/tree/main/.github ".github") | [.github](https://github.com/xjslang/xjs/tree/main/.github ".github") | [chore: add CI workflow](https://github.com/xjslang/xjs/commit/4709e654cd0fc2c79a09690f7b73eb3d8364503b "chore: add CI workflow") | Aug 17, 2026 |

| [.vscode](https://github.com/xjslang/xjs/tree/main/.vscode ".vscode") | [.vscode](https://github.com/xjslang/xjs/tree/main/.vscode ".vscode") | [refactor: concatenate pass/*.js files into a single check/general.js …](https://github.com/xjslang/xjs/commit/1087fd5626a3b5743a871c8f404686c301770736 "refactor: concatenate pass/*.js files into a single check/general.js file") | Aug 6, 2026 |

| [ast](https://github.com/xjslang/xjs/tree/main/ast "ast") | [ast](https://github.com/xjslang/xjs/tree/main/ast "ast") | [feat(parser): implement export statement](https://github.com/xjslang/xjs/commit/ac2370220bdb70e3d4a205593d775624695e72e1 "feat(parser): implement export statement") | Jul 11, 2026 |

| [examples](https://github.com/xjslang/xjs/tree/main/examples "examples") | [examples](https://github.com/xjslang/xjs/tree/main/examples "examples") | [refactor: move js into jsextended and rename jsextended it to js](https://github.com/xjslang/xjs/commit/9dcfbb991ceaf1df0c5d8c1a582713c8c7f1be9f "refactor: move js into jsextended and rename jsextended it to js") | Aug 25, 2026 |

| [internal](https://github.com/xjslang/xjs/tree/main/internal "internal") | [internal](https://github.com/xjslang/xjs/tree/main/internal "internal") | [refactor: move js into jsextended and rename jsextended it to js](https://github.com/xjslang/xjs/commit/9dcfbb991ceaf1df0c5d8c1a582713c8c7f1be9f "refactor: move js into jsextended and rename jsextended it to js") | Aug 25, 2026 |

| [js](https://github.com/xjslang/xjs/tree/main/js "js") | [js](https://github.com/xjslang/xjs/tree/main/js "js") | [fix: benchmarks](https://github.com/xjslang/xjs/commit/f3a5fb671e274eb6de1429d7521ceecd2ed7916b "fix: benchmarks") | Aug 28, 2026 |

| [magefiles](https://github.com/xjslang/xjs/tree/main/magefiles "magefiles") | [magefiles](https://github.com/xjslang/xjs/tree/main/magefiles "magefiles") | [refactor: move js into jsextended and rename jsextended it to js](https://github.com/xjslang/xjs/commit/9dcfbb991ceaf1df0c5d8c1a582713c8c7f1be9f "refactor: move js into jsextended and rename jsextended it to js") | Aug 25, 2026 |

| [parser](https://github.com/xjslang/xjs/tree/main/parser "parser") | [parser](https://github.com/xjslang/xjs/tree/main/parser "parser") | [refactor: move scanner into parser](https://github.com/xjslang/xjs/commit/0dea297b8ee180f6e27bb2afd8d0e6699a6d4eea "refactor: move scanner into parser") | Aug 27, 2026 |

| [printer](https://github.com/xjslang/xjs/tree/main/printer "printer") | [printer](https://github.com/xjslang/xjs/tree/main/printer "printer") | [refactor: move js into jsextended and rename jsextended it to js](https://github.com/xjslang/xjs/commit/9dcfbb991ceaf1df0c5d8c1a582713c8c7f1be9f "refactor: move js into jsextended and rename jsextended it to js") | Aug 25, 2026 |

| [scanner](https://github.com/xjslang/xjs/tree/main/scanner "scanner") | [scanner](https://github.com/xjslang/xjs/tree/main/scanner "scanner") | [refactor: move scanner into parser](https://github.com/xjslang/xjs/commit/0dea297b8ee180f6e27bb2afd8d0e6699a6d4eea "refactor: move scanner into parser") | Aug 27, 2026 |

| [testdata/bench](https://github.com/xjslang/xjs/tree/main/testdata/bench "This path skips through empty directories") | [testdata/bench](https://github.com/xjslang/xjs/tree/main/testdata/bench "This path skips through empty directories") | [test(benchm): compare XJS with Goja and tdewolff](https://github.com/xjslang/xjs/commit/9af2d75f67764ee4046dfef9bb50507e9ddad6b1 "test(benchm): compare XJS with Goja and tdewolff") | Aug 26, 2026 |

| [token](https://github.com/xjslang/xjs/tree/main/token "token") | [token](https://github.com/xjslang/xjs/tree/main/token "token") | [refactor: remove token.Scanner interface](https://github.com/xjslang/xjs/commit/21fce9f62ff3199c33a1ef89e7da032c91965410 "refactor: remove token.Scanner interface") | Aug 27, 2026 |

| [.agent.md](https://github.com/xjslang/xjs/blob/main/.agent.md ".agent.md") | [.agent.md](https://github.com/xjslang/xjs/blob/main/.agent.md ".agent.md") | [feat(docs): update parser philosophy section to clarify syntax vs sem…](https://github.com/xjslang/xjs/commit/fb9bbe590c38513934ebcca74ecdcc285a9cf4e3 "feat(docs): update parser philosophy section to clarify syntax vs semantics") | Jul 31, 2026 |

| [.gitattributes](https://github.com/xjslang/xjs/blob/main/.gitattributes ".gitattributes") | [.gitattributes](https://github.com/xjslang/xjs/blob/main/.gitattributes ".gitattributes") | [chore: add .gitattributes to enforce LF line endings](https://github.com/xjslang/xjs/commit/0783d6f4616830737214a03346aeaee1797ce4ba "chore: add .gitattributes to enforce LF line endings") | Aug 17, 2026 |

| [.gitignore](https://github.com/xjslang/xjs/blob/main/.gitignore ".gitignore") | [.gitignore](https://github.com/xjslang/xjs/blob/main/.gitignore ".gitignore") | [Implement sourcemap functionality](https://github.com/xjslang/xjs/commit/fd974c03a3afa8fda417a2641cea571d54ca0669 "Implement sourcemap functionality") | Dec 14, 2025 |

| [.golangci.yml](https://github.com/xjslang/xjs/blob/main/.golangci.yml ".golangci.yml") | [.golangci.yml](https://github.com/xjslang/xjs/blob/main/.golangci.yml ".golangci.yml") | [chore(linter): enable gofumpt and fix minor lint issues](https://github.com/xjslang/xjs/commit/8a7079fb2c394e3c341ed42bdacb43ea474a9556 "chore(linter): enable gofumpt and fix minor lint issues") | May 18, 2026 |

| [CONTRIBUTING.md](https://github.com/xjslang/xjs/blob/main/CONTRIBUTING.md "CONTRIBUTING.md") | [CONTRIBUTING.md](https://github.com/xjslang/xjs/blob/main/CONTRIBUTING.md "CONTRIBUTING.md") | [chore: setup mage](https://github.com/xjslang/xjs/commit/fc9153c8dedebe586f22746cfaa722b2ea24456b "chore: setup mage - Add magefile.go - Add Lint command - Setup pre-push") | Apr 6, 2026 |

| [LICENSE](https://github.com/xjslang/xjs/blob/main/LICENSE "LICENSE") | [LICENSE](https://github.com/xjslang/xjs/blob/main/LICENSE "LICENSE") | [Refactor xjslang: Remove parser_go.go and introduce token package](https://github.com/xjslang/xjs/commit/a76c8842e967df108756e1470d9ca12ec7e0d2f1 "Refactor xjslang: Remove parser_go.go and introduce token package - Deleted parser_go.go, consolidating the parser logic into a more structured format. - Added token package to define token types and structures used by the lexer and parser. - Created documentation for the token package, detailing token types and usage examples. - Introduced xjslang package to provide a simplified interface for lexing and parsing input. - Added Parse function for convenience, returning the AST program node and any parsing errors. - Established versioning for the xjslang package.") | Aug 13, 2025 |

| [README.md](https://github.com/xjslang/xjs/blob/main/README.md "README.md") | [README.md](https://github.com/xjslang/xjs/blob/main/README.md "README.md") | [docs: update README](https://github.com/xjslang/xjs/commit/4edd376582326fa19bfc2ff8ec8182b16ea57fdd "docs: update README") | Aug 28, 2026 |

| [go.mod](https://github.com/xjslang/xjs/blob/main/go.mod "go.mod") | [go.mod](https://github.com/xjslang/xjs/blob/main/go.mod "go.mod") | [test(benchm): compare XJS with Goja and tdewolff](https://github.com/xjslang/xjs/commit/9af2d75f67764ee4046dfef9bb50507e9ddad6b1 "test(benchm): compare XJS with Goja and tdewolff") | Aug 26, 2026 |

| [go.sum](https://github.com/xjslang/xjs/blob/main/go.sum "go.sum") | [go.sum](https://github.com/xjslang/xjs/blob/main/go.sum "go.sum") | [test(benchm): compare XJS with Goja and tdewolff](https://github.com/xjslang/xjs/commit/9af2d75f67764ee4046dfef9bb50507e9ddad6b1 "test(benchm): compare XJS with Goja and tdewolff") | Aug 26, 2026 |

| [xjs.go](https://github.com/xjslang/xjs/blob/main/xjs.go "xjs.go") | [xjs.go](https://github.com/xjslang/xjs/blob/main/xjs.go "xjs.go") | [refactor: move js into jsextended and rename jsextended it to js](https://github.com/xjslang/xjs/commit/9dcfbb991ceaf1df0c5d8c1a582713c8c7f1be9f "refactor: move js into jsextended and rename jsextended it to js") | Aug 25, 2026 |

| [xjs_bench_test.go](https://github.com/xjslang/xjs/blob/main/xjs_bench_test.go "xjs_bench_test.go") | [xjs_bench_test.go](https://github.com/xjslang/xjs/blob/main/xjs_bench_test.go "xjs_bench_test.go") | [test(benchm): compare XJS with Goja and tdewolff](https://github.com/xjslang/xjs/commit/9af2d75f67764ee4046dfef9bb50507e9ddad6b1 "test(benchm): compare XJS with Goja and tdewolff") | Aug 26, 2026 |

| [xjs_test.go](https://github.com/xjslang/xjs/blob/main/xjs_test.go "xjs_test.go") | [xjs_test.go](https://github.com/xjslang/xjs/blob/main/xjs_test.go "xjs_test.go") | [refactor(scanner): change UseScanner signature](https://github.com/xjslang/xjs/commit/fd7deceb284bbef747de0c230632a552c4d5f0e8 "refactor(scanner): change UseScanner signature") | Aug 24, 2026 | | View all files |

Repository files navigation

- README

- Contributing

- MIT license

More items

XJS (eXtensible JavaScript parser)

[](https://github.com/xjslang/xjs#xjs-extensible-javascript-parser)

A tool for creating JavaScript dialects.

Why XJS?

[](https://github.com/xjslang/xjs#why-xjs)

It all started with an innocent question: "Would it be possible to use `defer` (from Go) in JS?" And the answer is "Yes, but with caveats."

We could write a Babel plugin or extend Acorn to transpile `defer()` to JS. But those and other approaches shared a common problem: "the extension had to respect JS grammar rules." And `defer` didn't.

That's why I decided to build a JS parser capable of transpiling exotic or experimental features into standard JS.

**What can you do with XJS?**

You can create your own dialect without having to build a language from scratch. You'd simply add your own operators and statements to JS. The only limit is your imagination.

Examples

[](https://github.com/xjslang/xjs#examples)

Real-world dialects built with XJS:

- DJS - JavaScript with `defer`.

- HJS - JavaScript with native HTML tags.

See also the `examples/` directory for basic samples.

How does it work?

[](https://github.com/xjslang/xjs#how-does-it-work)

It works by intercepting the parsing flow at strategic points and adding custom **scanners**, **parsers**, and **printers**. This is done through the following methods:

- `scanner.Builder.UseScanner`: add your own custom tokens.

- `parser.Builder.UseStmtParser`: add your own statement parsers.

- `parser.Builder.UsePrefixOpParser`: add your own prefix operators.

- `parser.Builder.UseInfixOpParser`: add your own infix operators.

- `parser.Builder.UseExprParser`: add your own expression parsers (*).

- `printer.Builder.UsePrinter`: add your own node printers.

(*): You usually do not need `UseExprParser`, since `UsePrefixOpParser` and `UseInfixOpParser` are enough.

What is a Scanner, a Parser and a Printer?

[](https://github.com/xjslang/xjs#what-is-a-scanner-a-parser-and-a-printer)

The parsing process is divided into three responsibilities:

- `scanner.Scanner`: splits or "tokenizes" the input into tokens, which are later processed by the parser.

- `parser.Parser`: interprets the tokens and produces the AST (Abstract Syntax Tree).

- `printer.Printer`: turns AST nodes back into code, whether compiled, formatted, or otherwise. Each printer has a different purpose.

Benchmarks

[](https://github.com/xjslang/xjs#benchmarks)

undefinedshell go test -run="^$" -bench=BenchmarkCompare -benchmem -count=10 . > result.out benchstat -col /parser result.out undefined

Results (lower is faster):

``` Goja ░░░░░░░░░░░░░░░░░░░░░░░░░░░ (9.65% faster) tdewolff ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░ (2.37% faster) XJS ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░ ```

**How to interpret the results?**

Comparisons are tricky, especially when the tools being compared serve different purposes. Therefore, the results above simply tell us that XJS is fast enough and uses memory and CPU resources in a modest way. Nothing more :)