!NPM

CJS Module Lexer (Rust)

This is a rewrite of cjs-module-lexer in Rust. It is a CommonJS lexer used to detect the most likely list of named exports of a CommonJS module.

Online Playground

CJS Module Lexer Playground

Installation

$3

#### With Package Managers

``
npm i cjs-module-lexer-rs
`

`
yarn add cjs-module-lexer-rs
`

`
pnpm add cjs-module-lexer-rs
`

#### With esm.sh

`js
import { init, parse } from "https://esm.sh/cjs-module-lexer-rs";
`

$3

Coming soon...

Get Started

$3

`js
// example.js
const { init, parse } = require("cjs-module-lexer-rs");

const code =
module.exports.asdf = 'asdf';
exports = 'asdf';
module.exports = require('./asdf');
if (maybe)
module.exports = require("./another");
;

init().then(() => console.log(parse(code, 'filename.js')));
`

`js
{
imports: [ './asdf', './another'],
exports: [ 'asdf' ],
reexports: [ './another' ],
errors: []
}
`

$3

`html











`

`json
{
"imports": [
"./asdf",
"./another",
],
"exports": [
"asdf"
],
"reexports": [
"./another"
],
"errors": []
}
`




The Why


The frontend tooling has migrated to usage of moderm native languages to accelerate development and improve developer experience. cjs-module-lexer remains useful in many scenes, but it assumes the code is UTF16 and only allows single-thread. Making cjs-module-lexer working with Rust requires FFI and unsafe code. Hopefully this Rust library will be useful for Rust tooling authors to interop between CJS and ESM.

Features

| Feature | Status | Since | Note |
|---|---|---|---|
| exports.asdf = x | 👌 | 0.1.0 |
| exports['asdf'] = x | 👌 | 0.1.0 |
| module.exports = { ... } | 👌 | 0.1.0 | { ... } is like { a, b, c: d }, where d is Literal or Identifier |
| require('module') | 👌 | 0.1.0 |
| Object.defineProperty(exports, 'q', { enumerable: true, get() { return q } }) | 👷 | | TypeScript: export {colorFactory} from './color-factory';
| __export, __exportStar | 👷 | | TypeScript: export * from 'external' |
| Skip StringLiteral | 👌 | 0.1.0 |
| Skip RegularExpressionLiteral | 👌 | 0.1.0
| Skip Template | 👌 | 0.1.0
| Non-unicode Named Export | ❌ | | Not supported due to std::str only allows unicode strings

Reference

https://babeljs.io/docs/en/babel-plugin-transform-modules-commonjs




Benchmarks

$3

`
cargo bench

test tests::bench_angular ... bench: 5,176,437 ns/iter (+/- 260,598)
test tests::bench_angular_min ... bench: 2,321,468 ns/iter (+/- 939,693)
test tests::bench_d3 ... bench: 3,155,154 ns/iter (+/- 182,490)
test tests::bench_d3_min ... bench: 1,897,146 ns/iter (+/- 100,576)
test tests::bench_magic_string ... bench: 209,630 ns/iter (+/- 11,577)
test tests::bench_magic_string_min ... bench: 145,834 ns/iter (+/- 7,527)
test tests::bench_rollup ... bench: 3,918,989 ns/iter (+/- 130,726)
test tests::bench_rollup_min ... bench: 2,637,478 ns/iter (+/- 74,449)
``