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, runtime) { // webpackBootstrap
/******/ 	"use strict";
/******/ 	// 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;
/******/ 	}
/******/
/******/
/******/
/******/ 	// the startup function
/******/ 	function startup() {
/******/ 		// Load entry module and return exports
/******/ 		return __webpack_require__(0);
/******/ 	};
/******/
/******/ 	// run startup
/******/ 	return startup();
/******/ })
/************************************************************************/

/******/ ([
/* 0 */
/*!********************!*\
  !*** ./example.js ***!
  \********************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: __webpack_require____webpack_exports__,  */
/***/ (function(__unusedmodule, 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" ***!
  \**********************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: module */
/***/ (function(module) {

module.exports = __WEBPACK_EXTERNAL_MODULE__1__;

/***/ }),
/* 2 */
/*!***************************************************************************************************************!*\
  !*** external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} ***!
  \***************************************************************************************************************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: module */
/***/ (function(module) {

module.exports = __WEBPACK_EXTERNAL_MODULE__2__;

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

Info

Unoptimized

Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-alpha.11
    Asset      Size  Chunks             Chunk Names
output.js  3.13 KiB     {0}  [emitted]  main
Entrypoint main = output.js
chunk {0} output.js (main) 194 bytes [entry] [rendered]
    > ./example.js main
 [0] ./example.js 110 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-alpha.11
    Asset       Size  Chunks             Chunk Names
output.js  708 bytes   {179}  [emitted]  main
Entrypoint main = output.js
chunk {179} output.js (main) 194 bytes [entry] [rendered]
    > ./example.js main
 [144] ./example.js 110 bytes {179} [built]
       entry ./example.js main
 [324] external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} 42 bytes {179} [built]
       cjs require subtract [144] ./example.js 2:15-34
 [630] external "add" 42 bytes {179} [built]
       cjs require add [144] ./example.js 1:10-24