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

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

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

# webpack.config.js

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

# dist/output.js

```javascript
(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 /******/ (() => { // webpackBootstrap
/******/ 	var __webpack_modules__ = ([
/* 0 */
/*!********************!*\
  !*** ./example.js ***!
  \********************/
/*! exports [maybe provided (runtime-defined)] [maybe used (runtime-defined)] */
/*! runtime requirements: __webpack_require__, __webpack_exports__ */
/***/ ((__unused_webpack_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" ***!
  \**********************/
/*! 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"} ***!
  \***************************************************************************************************************/
/*! exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: module */
/***/ ((module) => {

"use strict";
module.exports = __WEBPACK_EXTERNAL_MODULE__2__;

/***/ })
/******/ 	]);
/************************************************************************/
/******/ 	// The module cache
/******/ 	var __webpack_module_cache__ = {};
/******/ 	
/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {
/******/ 		// Check if module is in cache
/******/ 		if(__webpack_module_cache__[moduleId]) {
/******/ 			return __webpack_module_cache__[moduleId].exports;
/******/ 		}
/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = __webpack_module_cache__[moduleId] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};
/******/ 	
/******/ 		// Execute the module function
/******/ 		__webpack_modules__[moduleId](module, module.exports, __webpack_require__);
/******/ 	
/******/ 		// Flag the module as loaded
/******/ 		module.l = true;
/******/ 	
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/ 	
/************************************************************************/
/******/ 	// module exports must be returned from runtime so entry inlining is disabled
/******/ 	// startup
/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(0);
/******/ })()
;
});
```

# Info

## Unoptimized

```
Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-beta.1
    Asset      Size
output.js  3.18 KiB  [emitted]  [name: main]
Entrypoint main = output.js
chunk output.js (main) 194 bytes [entry] [rendered]
    > ./example.js main
 ./example.js 110 bytes [built]
     entry ./example.js main
     used a library export
 external "add" 42 bytes [built]
     [used exports unknown]
     cjs require add ./example.js 1:10-24
 external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} 42 bytes [built]
     [used exports unknown]
     cjs require subtract ./example.js 2:15-34
```

## Production mode

```
Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-beta.1
    Asset       Size
output.js  668 bytes  [emitted]  [name: main]
Entrypoint main = output.js
chunk output.js (main) 194 bytes [entry] [rendered]
    > ./example.js main
 ./example.js 110 bytes [built]
     entry ./example.js main
     used a library export
 external "add" 42 bytes [built]
     cjs require add ./example.js 1:10-24
 external {"root":"subtract","commonjs2":"./subtract","commonjs":["./math","subtract"],"amd":"subtract"} 42 bytes [built]
     cjs require subtract ./example.js 2:15-34
```
