webpack/examples/externals

This example demonstrates how to build a library with webpack that has dependencies on 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 the 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];
	}
})(self, function(__WEBPACK_EXTERNAL_MODULE__1__, __WEBPACK_EXTERNAL_MODULE__2__) {
return /******/ (() => { // webpackBootstrap
/******/ 	var __webpack_modules__ = ([
/* 0 */,
/* 1 */
/*!**********************!*\
  !*** external "add" ***!
  \**********************/
/*! dynamic exports */
/*! exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: module */
/***/ ((module) => {

"use strict";
module.exports = __WEBPACK_EXTERNAL_MODULE__1__;

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

"use strict";
module.exports = __WEBPACK_EXTERNAL_MODULE__2__;

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

/* webpack runtime code */

/************************************************************************/
/******/ 	// The module cache
/******/ 	var __webpack_module_cache__ = {};
/******/ 	
/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {
/******/ 		// Check if module is in cache
/******/ 		var cachedModule = __webpack_module_cache__[moduleId];
/******/ 		if (cachedModule !== undefined) {
/******/ 			return cachedModule.exports;
/******/ 		}
/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = __webpack_module_cache__[moduleId] = {
/******/ 			// no module.id needed
/******/ 			// no module.loaded needed
/******/ 			exports: {}
/******/ 		};
/******/ 	
/******/ 		// Execute the module function
/******/ 		__webpack_modules__[moduleId](module, module.exports, __webpack_require__);
/******/ 	
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/ 	
/************************************************************************/

var __webpack_exports__ = {};
// This entry need to be wrapped in an IIFE because it need to be isolated against other modules in the chunk.
(() => {
var exports = __webpack_exports__;
/*!********************!*\
  !*** ./example.js ***!
  \********************/
/*! default exports */
/*! export exampleValue [provided] [maybe used in main (runtime-defined)] [usage prevents renaming] */
/*! other exports [not provided] [maybe used in main (runtime-defined)] */
/*! runtime requirements: __webpack_exports__, __webpack_require__ */
var add = __webpack_require__(/*! add */ 1);
var subtract = __webpack_require__(/*! subtract */ 2);

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

/******/ 	return __webpack_exports__;
/******/ })()
;
});

Info

Unoptimized

asset output.js 3.28 KiB [emitted] (name: main)
chunk (runtime: main) output.js (main) 194 bytes [entry] [rendered]
  > ./example.js main
  dependent modules 84 bytes [dependent] 2 modules
  ./example.js 110 bytes [built] [code generated]
    [exports: exampleValue]
    [used exports unknown]
    entry ./example.js main
    used as library export
webpack 5.51.1 compiled successfully

Production mode

asset output.js 679 bytes [emitted] [minimized] (name: main)
chunk (runtime: main) output.js (main) 194 bytes [entry] [rendered]
  > ./example.js main
  dependent modules 84 bytes [dependent] 2 modules
  ./example.js 110 bytes [built] [code generated]
    [exports: exampleValue]
    entry ./example.js main
    used as library export
webpack 5.51.1 compiled successfully