webpack/examples/externals

This example demonstrates how to build a library with webpack that has dependencies to other libraries which should not be included in the compiled version.

We use the libraryTarget: "umd" option to build a UMD module that is consumable in CommonJs, AMD and with script tags. We don't specify the library option so the library is exported to the root namespace.

We use the externals option to define dependencies that should be resolved in the target environment.

In the simple case we just need to specify a string ("add"). Then it's resolved as "add" module in CommonJs and AMD, and as global add when used with script tag.

In the complex case we specify different values for each environment:

environment	config value	resolved as
CommonJs (strict)	["./math", "subtract"]	require("./math").subtract
CommonJs (node.js)	"./subtract"	require("./subtract")
AMD	"subtract"	define(["subtract"], ...)
script tag	"subtract"	this.subtract

example.js

var add = require("add");
var subtract = require("subtract");

exports.exampleValue = subtract(add(42, 2), 2);

webpack.config.js

module.exports = {
	// mode: "development || "production",
	output: {
		libraryTarget: "umd"
	},
	externals: [
		"add",
		{
			subtract: {
				root: "subtract",
				commonjs2: "./subtract",
				commonjs: ["./math", "subtract"],
				amd: "subtract"
			}
		}
	]
};

dist/output.js

(function webpackUniversalModuleDefinition(root, factory) {
	if(typeof exports === 'object' && typeof module === 'object')
		module.exports = factory(require("add"), require("./subtract"));
	else if(typeof define === 'function' && define.amd)
		define(["add", "subtract"], factory);
	else {
		var a = typeof exports === 'object' ? factory(require("add"), require("./math")["subtract"]) : factory(root["add"], root["subtract"]);
		for(var i in a) (typeof exports === 'object' ? exports : root)[i] = a[i];
	}
})(window, function(__WEBPACK_EXTERNAL_MODULE__1__, __WEBPACK_EXTERNAL_MODULE__2__) {

return /******/ (function(modules) { /* webpackBootstrap */ })

return /******/ (function(modules) { // webpackBootstrap
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/
/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {
/******/
/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId]) {
/******/ 			return installedModules[moduleId].exports;
/******/ 		}
/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};
/******/
/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
/******/
/******/ 		// Flag the module as loaded
/******/ 		module.l = true;
/******/
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/
/******/
/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;
/******/
/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;
/******/
/******/ 	// define getter function for harmony exports
/******/ 	__webpack_require__.d = function(exports, name, getter) {
/******/ 		if(!__webpack_require__.o(exports, name)) {
/******/ 			Object.defineProperty(exports, name, { enumerable: true, get: getter });
/******/ 		}
/******/ 	};
/******/
/******/ 	// define __esModule on exports
/******/ 	__webpack_require__.r = function(exports) {
/******/ 		if(typeof Symbol !== 'undefined' && Symbol.toStringTag) {
/******/ 			Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
/******/ 		}
/******/ 		Object.defineProperty(exports, '__esModule', { value: true });
/******/ 	};
/******/
/******/ 	// create a fake namespace object
/******/ 	// mode & 1: value is a module id, require it
/******/ 	// mode & 2: merge all properties of value into the ns
/******/ 	// mode & 4: return value when already ns object
/******/ 	// mode & 8|1: behave like require
/******/ 	__webpack_require__.t = function(value, mode) {
/******/ 		if(mode & 1) value = __webpack_require__(value);
/******/ 		if(mode & 8) return value;
/******/ 		if((mode & 4) && typeof value === 'object' && value && value.__esModule) return value;
/******/ 		var ns = Object.create(null);
/******/ 		__webpack_require__.r(ns);
/******/ 		Object.defineProperty(ns, 'default', { enumerable: true, value: value });
/******/ 		if(mode & 2 && typeof value != 'string') for(var key in value) __webpack_require__.d(ns, key, function(key) { return value[key]; }.bind(null, key));
/******/ 		return ns;
/******/ 	};
/******/
/******/ 	// getDefaultExport function for compatibility with non-harmony modules
/******/ 	__webpack_require__.n = function(module) {
/******/ 		var getter = module && module.__esModule ?
/******/ 			function getDefault() { return module['default']; } :
/******/ 			function getModuleExports() { return module; };
/******/ 		__webpack_require__.d(getter, 'a', getter);
/******/ 		return getter;
/******/ 	};
/******/
/******/ 	// Object.prototype.hasOwnProperty.call
/******/ 	__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
/******/
/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "dist/";
/******/
/******/
/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(__webpack_require__.s = 0);
/******/ })
/************************************************************************/

/******/ ([
/* 0 */
/*!********************!*\
  !*** ./example.js ***!
  \********************/
/*! no static exports found */
/***/ (function(module, exports, __webpack_require__) {

var add = __webpack_require__(/*! add */ 1);
var subtract = __webpack_require__(/*! subtract */ 2);

exports.exampleValue = subtract(add(42, 2), 2);

/***/ }),
/* 1 */
/*!**********************!*\
  !*** external "add" ***!
  \**********************/
/*! no static exports found */
/***/ (function(module, exports) {

module.exports = __WEBPACK_EXTERNAL_MODULE__1__;

/***/ }),
/* 2 */
/*!***************************************************************************************************************!*\
  !*** external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} ***!
  \***************************************************************************************************************/
/*! no static exports found */
/***/ (function(module, exports) {

module.exports = __WEBPACK_EXTERNAL_MODULE__2__;

/***/ })
/******/ ]);
});

Info

Unoptimized

Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-next
    Asset      Size  Chunks             Chunk Names
output.js  5.13 KiB       0  [emitted]  main
Entrypoint main = output.js
chunk    {0} output.js (main) 197 bytes [entry] [rendered]
    > .\example.js main
 [0] ./example.js 113 bytes {0} [built]
     [used exports unknown]
     entry .\example.js  main
 [1] external "add" 42 bytes {0} [built]
     [used exports unknown]
     cjs require add [0] ./example.js 1:10-24
 [2] external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} 42 bytes {0} [built]
     [used exports unknown]
     cjs require subtract [0] ./example.js 2:15-34

Production mode

Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-next
    Asset     Size  Chunks             Chunk Names
output.js  1.4 KiB       0  [emitted]  main
Entrypoint main = output.js
chunk    {0} output.js (main) 197 bytes [entry] [rendered]
    > .\example.js main
 [0] ./example.js 113 bytes {0} [built]
     entry .\example.js  main
 [1] external "add" 42 bytes {0} [built]
     cjs require add [0] ./example.js 1:10-24
 [2] external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} 42 bytes {0} [built]
     cjs require subtract [0] ./example.js 2:15-34