babel-plugin-transform-es2015-modules-commonjs

What is babel-plugin-transform-es2015-modules-commonjs?

The babel-plugin-transform-es2015-modules-commonjs npm package is a plugin for Babel that transforms ECMAScript 2015 modules to CommonJS syntax. This allows developers to write their JavaScript code using the ES2015 module syntax and then compile it down to a format that is compatible with environments that only support CommonJS modules, such as Node.js.

What are babel-plugin-transform-es2015-modules-commonjs's main functionalities?

Transform ES2015 import statements to CommonJS require

This feature allows developers to use the ES2015 import syntax and have it compiled into CommonJS require statements.

import { square } from './math';
// Transforms to:
var _math = require('./math');
var square = _math.square;

Transform ES2015 export statements to CommonJS exports

This feature enables the use of ES2015 export syntax which is then compiled into CommonJS exports.

export const square = (n) => n * n;
// Transforms to:
exports.square = (n) => n * n;

Other packages similar to babel-plugin-transform-es2015-modules-commonjs

@babel/plugin-transform-modules-commonjs

This package is the evolution of babel-plugin-transform-es2015-modules-commonjs and is maintained by the Babel team. It provides similar functionality but is updated to work with newer versions of Babel and may include additional optimizations and features.

esm

The esm package is a lightweight runtime that allows you to load ES modules in Node.js without any compilation step. It differs from babel-plugin-transform-es2015-modules-commonjs in that it doesn't transform the code but rather enables an environment where ES modules can be used natively.

README

babel-plugin-transform-es2015-modules-commonjs

This plugin transforms ES2015 modules to CommonJS.

Babel 6 Changes

Babel 6 changed some behavior by not doing module.exports = exports['default'] anymore in the modules transforms.

There are some caveats, but you can use babel-plugin-add-module-exports, so that updating to Babel 6 isn't a breaking change since users that don't use ES modules don't have to do require("your-module").default.

However, it may not match how Node eventually implements ES modules natively given the the current proposal.

Example

In

export default 42;

Out

Object.defineProperty(exports, "__esModule", {
  value: true
});

exports.default = 42;

Installation

npm install --save-dev babel-plugin-transform-es2015-modules-commonjs

Usage

Via .babelrc (Recommended)

.babelrc

// without options
{
  "plugins": ["transform-es2015-modules-commonjs"]
}

// with options
{
  "plugins": [
    ["transform-es2015-modules-commonjs", {
      "allowTopLevelThis": true
    }]
  ]
}

Via CLI

babel --plugins transform-es2015-modules-commonjs script.js

Via Node API

require("babel-core").transform("code", {
  plugins: ["transform-es2015-modules-commonjs"]
});

Options

loose

boolean, defaults to false.

As per the spec, import and export are only allowed to be used at the top level. When in loose mode these are allowed to be used anywhere.

And by default, when using exports with babel a non-enumerable __esModule property is exported.

var foo = exports.foo = 5;

Object.defineProperty(exports, "__esModule", {
  value: true
});

In environments that don't support this you can enable loose mode on babel-plugin-transform-es2015-modules-commonjs and instead of using Object.defineProperty an assignment will be used instead.

var foo = exports.foo = 5;
exports.__esModule = true;

strict

boolean, defaults to false

By default, when using exports with babel a non-enumerable __esModule property is exported. In some cases this property is used to determine if the import is the default export or if it contains the default export.

var foo = exports.foo = 5;

Object.defineProperty(exports, "__esModule", {
  value: true
});

In order to prevent the __esModule property from being exported, you can set the strict option to true.

noInterop

boolean, defaults to false

By default, when using exports with babel a non-enumerable __esModule property is exported. This property is then used to determine if the import is the default export or if it contains the default export.

"use strict";

var _foo = require("foo");

var _foo2 = _interopRequireDefault(_foo);

function _interopRequireDefault(obj) {
  return obj && obj.__esModule ? obj : { default: obj };
}

In cases where the auto-unwrapping of default is not needed, you can set the noInterop option to true to avoid the usage of the interopRequireDefault helper (shown in inline form above).