cjs-es

Transform CommonJS module into ES module.

Features

• Lightweight.

• Prefer named import/export when possible.

• Only support the syntax that is interchangeable between mjs and js.

• Convert in-place. It only converts:

  • top-level require declaration (const foo = require("foo")),
  • top-level module.exports, exports assignment (module.exports = .../const foo = exports.foo = ...),
  • dynamic-require expression (Promise.resolve(require("foo"))).

  There are more samples under test/cases folder.

Usage

const {parse} = require("acorn");
const {transform} = require("cjs-es");
const {code} = transform({
  parse,
  code: `
function foo() {}
function bar() {}
module.exports = {foo, bar};
`
});
/* code == `
function foo() {}
function bar() {}
export {foo};
export {bar};
` */

Import style

When binding the module into one identifier:

const foo = require("foo");

The transformer imports all members from the module by the default:

import * as foo from "foo";

To import the default member, add // default comment:

const foo = require("foo"); // default

Result:

import foo from "foo";

Export style

If the module.exports is assigned with an object pattern:

const foo = "foo";
const bar = "bar";
module.exports = {
  foo,
  bar
};

The transformer converts it into named exports:

const foo = "foo";
const bar = "bar";
export {foo};
export {bar};

If you like to export the entire object as the default member, you can use // default comment at the line of module.exports:

const foo = "foo";
const bar = "bar";
module.exports = { // default
  foo,
  bar
};

Result:

const foo = "foo";
const bar = "bar";
export default {
  foo,
  bar
};

API reference

This module exports following members.

• transform: A function which can convert CJS module synax into ES module syntax.

transform(options?: object): TransformResult object

options has following members:

• parse: function. A parser function which can parse JavaScript code into ESTree.

• code: string. The JavaScript source code.

• sourceMap?: boolean. If true then generate the source map. Default: false

• importStyle?: string or function -> string. The result must be "named" or "default". Default: "named"

  When the value is a function, it recieves one argument:

  • moduleId: string. The module ID of require("module-id").

• exportStyle?: string or function -> string. The result must be "named" or "default". Default: "named"

The result object has following members:

• code: string. The result JavaScript code.
• map?: object. The source map object generated by magicString.generateMap.

Changelog

• 0.2.0 (Apr 26, 2018)

  • Change: don't suppress parse error.
  • Change: remove // all comment.
  • Add: importStyle, exportStyle option.
  • Add: use // default to change import/export style.

• 0.1.0 (Apr 25, 2018)

  • Initial release.