esm-cjs-lexer

A commonjs module lexer written in Rust for detecting the module.exports of a commonjs module. The lexer is powered by swc, compiled to WebAssembly.

Usage

esm-cjs-lexer currently only supports Node.js environment. You can install it via npm CLI:

``bash
npm i esm-cjs-lexer
`

esm-cjs-lexer provides a parse function that detects the module.exports of a commonjs module. The function returns an object with two properties: exports and reexports. The exports property is an array of the exported names, and the reexports property is an array of the reexported modules.

`js
const { parse } = require("esm-cjs-lexer");

// named exports by assignment
// exports: ["a", "b", "c", "__esModule", "foo"]
const { exports } = parse("index.cjs",
exports.a = "a";
module.exports.b = "b";
Object.defineProperty(exports, "c", { value: 1 });
Object.defineProperty(module.exports, "__esModule", { value: true })
const key = "foo"
Object.defineProperty(exports, key, { value: "e" });
);

// reexports
// reexports: ["./lib"]
const { reexports } = parse("index.cjs",
module.exports = require("./lib");
);

// object exports(spread syntax supported)
// exports: ["foo", "baz"]
// reexports: ["./lib"]
const { exports, reexports } = parse("index.cjs",
const foo = "bar"
const obj = { baz: 123 }
module.exports = { foo, ...obj, ...require("./lib") };
);

// if expression
// exports: ["foo", "cjs"]
const { exports } = parse("index.cjs",
module.exports.a = "a";
if (true) {
exports.foo = "bar";
}
const mtype = "cjs";
if (mtype === "cjs") {
exports.cjs = true;
} else {
exports.esm = true;
}
if (false) {
exports.unreachable = true;
}
);

// condition exports by checking if process.env.NODE_ENV equals to nodeEnv option
// reexports: ["./index.development.js"]
const { reexports } = parse("index.cjs",
if (process.env.NODE_ENV === "development") {
module.exports = require("./index.development.js")
} else {
module.exports = require("./index.production.js")
}
, { nodeEnv: "development" });

// block&IIFE
// exports: ["foo", "baz", "__esModule"]
const { exports } = parse("index.cjs",
{
exports.foo = 'bar'
}
(function () {
exports.baz = 'qux'
if (true) {
return
}
exports.unreachable = true
})();
exports.__esModule = true
);

// UMD format
// exports: ["foo"]
const { exports } = parse("index.cjs",
(function (global, factory) {
typeof exports === "object" && typeof module !== "undefined" ? factory(exports) :
typeof define === "function" && define.amd ? define(["exports"], factory) :
(factory((global.MMDParser = global.MMDParser || {})));
}(this, function (exports) {
exports.foo = "bar";
}))
);

// exports by calling a function
// exports: ["foo"]
const { exports } = parse("index.cjs",
function module() {
return { foo: "bar" }
}
module.exports = module()
);

// annotated export names for ESM import
// exports: ["foo", "bar"]
const { exports } = parse("lib.cjs",
0 && (module.exports = {
foo,
bar,
})
);

// call reexports
// reexports: ["./lib()"]
const { reexports } = parse("index.cjs",
module.exports = require("./lib")()
);
// apply call reexports
// exports: ["foo"]
const { exports } = parse("lib.cjs",
module.exports = function() {
return { foo: "bar" }
}
, { callMode: true });
`

The parse function has the following types definition:

`ts
export function parse(
specifier: string,
code: string,
options? {
nodeEnv?: 'development' | 'production',
callMode?: boolean,
}
): {
exports: string[],
reexports: string[],
};
`

Development Setup

You will need rust 1.56+ and wasm-pack.

Build

`bash
wasm-pack build --target nodejs
`

Run tests

`bash
cargo test --all
``