This example demonstrates Scope Hoisting in combination with Code Splitting.

This is the dependency graph for the example: (solid lines express sync imports, dashed lines async imports)

![](graph.png)

All modules except `cjs` are EcmaScript modules. `cjs` is a CommonJS module.

The interesting thing here is that putting all modules in a single scope won't work, because of multiple reasons:

- Modules `lazy`, `c`, `d` and `cjs` need to be in a separate chunk
- Module `shared` is accessed by two chunks (different scopes)
- Module `cjs` is a CommonJs module

![](graph2.png)

Webpack, therefore, uses a approach called **"Partial Scope Hoisting"** or "Module concatenation", which chooses the largest possible subsets of ES modules which can be scope hoisted and combines them with the default webpack primitives.

![](graph3.png)

While module concatenation identifiers in modules are renamed to avoid conflicts and internal imports are simplified. External imports and exports from the root module use the existing ESM constructs.

# example.js

```javascript
import { a, x, y } from "a";
import * as b from "b";

import("./lazy").then(function(lazy) {
	console.log(a, b.a(), x, y, lazy.c, lazy.d.a, lazy.x, lazy.y);
});
```

# lazy.js

```javascript
export * from "c";
import * as d from "d";
export { d };
```

# a.js

```javascript
// module a
export var a = "a";
export * from "shared";
```

# b.js

```javascript
// module b
export function a() {
	return "b";
};
```

# c.js

```javascript
// module c
import { c as e } from "cjs";

export var c = String.fromCharCode(e.charCodeAt(0) - 2);

export { x, y } from "shared";
```

# d.js

```javascript
// module d
export var a = "d";
```

# cjs.js

```javascript
// module cjs (commonjs)
exports.c = "e";
```

# shared.js

```javascript
// shared module
export var x = "x";
export * from "shared2";
```

# shared2.js

```javascript
// shared2 module
export var y = "y";
```

# webpack.config.js

```javascript
"use strict";

/** @type {import("webpack").Configuration} */
const config = {
	// mode: "development" || "production",
	optimization: {
		usedExports: true,
		concatenateModules: true,
		chunkIds: "named" // To keep filename consistent between different modes (for example building only)
	}
};

module.exports = config;
```

# dist/output.js

```javascript
/******/ (() => { // webpackBootstrap
/******/ 	"use strict";
/******/ 	var __webpack_modules__ = ([
/* 0 */,
/* 1 */
/*!********************************************!*\
  !*** ./node_modules/shared.js + 1 modules ***!
  \********************************************/
/*! namespace exports */
/*! export x [provided] [used in main] [could be renamed] */
/*! export y [provided] [used in main] [could be renamed] -> ./node_modules/shared2.js .y */
/*! runtime requirements: __webpack_exports__, __webpack_require__.d, __webpack_require__.* */
/***/ ((__unused_webpack_module, __webpack_exports__, __webpack_require__) => {


// EXPORTS
__webpack_require__.d(__webpack_exports__, {
  x: () => (/* binding */ x),
  y: () => (/* reexport */ y)
});

;// ./node_modules/shared2.js
// shared2 module
var y = "y";

;// ./node_modules/shared.js
// shared module
var x = "x";



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

<details><summary><code>/* webpack runtime code */</code></summary>

``` js
/************************************************************************/
/******/ 	// 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;
/******/ 		}
/******/ 		// Check if module exists (development only)
/******/ 		if (__webpack_modules__[moduleId] === undefined) {
/******/ 			var e = new Error("Cannot find module '" + moduleId + "'");
/******/ 			e.code = 'MODULE_NOT_FOUND';
/******/ 			throw e;
/******/ 		}
/******/ 		// 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;
/******/ 	}
/******/ 	
/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = __webpack_modules__;
/******/ 	
/************************************************************************/
/******/ 	/* webpack/runtime/define property getters */
/******/ 	(() => {
/******/ 		// define getter functions for harmony exports
/******/ 		__webpack_require__.d = (exports, definition) => {
/******/ 			for(var key in definition) {
/******/ 				if(__webpack_require__.o(definition, key) && !__webpack_require__.o(exports, key)) {
/******/ 					Object.defineProperty(exports, key, { enumerable: true, get: definition[key] });
/******/ 				}
/******/ 			}
/******/ 		};
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/ensure chunk */
/******/ 	(() => {
/******/ 		__webpack_require__.f = {};
/******/ 		// This file contains only the entry chunk.
/******/ 		// The chunk loading function for additional chunks
/******/ 		__webpack_require__.e = (chunkId) => {
/******/ 			return Promise.all(Object.keys(__webpack_require__.f).reduce((promises, key) => {
/******/ 				__webpack_require__.f[key](chunkId, promises);
/******/ 				return promises;
/******/ 			}, []));
/******/ 		};
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/get javascript chunk filename */
/******/ 	(() => {
/******/ 		// This function allow to reference async chunks
/******/ 		__webpack_require__.u = (chunkId) => {
/******/ 			// return url for filenames based on template
/******/ 			return "" + chunkId + ".output.js";
/******/ 		};
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/hasOwnProperty shorthand */
/******/ 	(() => {
/******/ 		__webpack_require__.o = (obj, prop) => (Object.prototype.hasOwnProperty.call(obj, prop))
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/load script */
/******/ 	(() => {
/******/ 		var inProgress = {};
/******/ 		// data-webpack is not used as build has no uniqueName
/******/ 		// loadScript function to load a script via script tag
/******/ 		__webpack_require__.l = (url, done, key, chunkId) => {
/******/ 			if(inProgress[url]) { inProgress[url].push(done); return; }
/******/ 			var script, needAttach;
/******/ 			if(key !== undefined) {
/******/ 				var scripts = document.getElementsByTagName("script");
/******/ 				for(var i = 0; i < scripts.length; i++) {
/******/ 					var s = scripts[i];
/******/ 					if(s.getAttribute("src") == url) { script = s; break; }
/******/ 				}
/******/ 			}
/******/ 			if(!script) {
/******/ 				needAttach = true;
/******/ 				script = document.createElement('script');
/******/ 		
/******/ 				script.charset = 'utf-8';
/******/ 				if (__webpack_require__.nc) {
/******/ 					script.setAttribute("nonce", __webpack_require__.nc);
/******/ 				}
/******/ 		
/******/ 		
/******/ 				script.src = url;
/******/ 			}
/******/ 			inProgress[url] = [done];
/******/ 			var onScriptComplete = (prev, event) => {
/******/ 				// avoid mem leaks in IE.
/******/ 				script.onerror = script.onload = null;
/******/ 				clearTimeout(timeout);
/******/ 				var doneFns = inProgress[url];
/******/ 				delete inProgress[url];
/******/ 				script.parentNode && script.parentNode.removeChild(script);
/******/ 				doneFns && doneFns.forEach((fn) => (fn(event)));
/******/ 				if(prev) return prev(event);
/******/ 			}
/******/ 			var timeout = setTimeout(onScriptComplete.bind(null, undefined, { type: 'timeout', target: script }), 120000);
/******/ 			script.onerror = onScriptComplete.bind(null, script.onerror);
/******/ 			script.onload = onScriptComplete.bind(null, script.onload);
/******/ 			needAttach && document.head.appendChild(script);
/******/ 		};
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/make namespace object */
/******/ 	(() => {
/******/ 		// define __esModule on exports
/******/ 		__webpack_require__.r = (exports) => {
/******/ 			if(typeof Symbol !== 'undefined' && Symbol.toStringTag) {
/******/ 				Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
/******/ 			}
/******/ 			Object.defineProperty(exports, '__esModule', { value: true });
/******/ 		};
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/publicPath */
/******/ 	(() => {
/******/ 		__webpack_require__.p = "dist/";
/******/ 	})();
/******/ 	
/******/ 	/* webpack/runtime/jsonp chunk loading */
/******/ 	(() => {
/******/ 		// no baseURI
/******/ 		
/******/ 		// object to store loaded and loading chunks
/******/ 		// undefined = chunk not loaded, null = chunk preloaded/prefetched
/******/ 		// [resolve, reject, Promise] = chunk loading, 0 = chunk loaded
/******/ 		var installedChunks = {
/******/ 			"main": 0
/******/ 		};
/******/ 		
/******/ 		__webpack_require__.f.j = (chunkId, promises) => {
/******/ 				// JSONP chunk loading for javascript
/******/ 				var installedChunkData = __webpack_require__.o(installedChunks, chunkId) ? installedChunks[chunkId] : undefined;
/******/ 				if(installedChunkData !== 0) { // 0 means "already installed".
/******/ 		
/******/ 					// a Promise means "currently loading".
/******/ 					if(installedChunkData) {
/******/ 						promises.push(installedChunkData[2]);
/******/ 					} else {
/******/ 						if(true) { // all chunks have JS
/******/ 							// setup Promise in chunk cache
/******/ 							var promise = new Promise((resolve, reject) => (installedChunkData = installedChunks[chunkId] = [resolve, reject]));
/******/ 							promises.push(installedChunkData[2] = promise);
/******/ 		
/******/ 							// start chunk loading
/******/ 							var url = __webpack_require__.p + __webpack_require__.u(chunkId);
/******/ 							// create error before stack unwound to get useful stacktrace later
/******/ 							var error = new Error();
/******/ 							var loadingEnded = (event) => {
/******/ 								if(__webpack_require__.o(installedChunks, chunkId)) {
/******/ 									installedChunkData = installedChunks[chunkId];
/******/ 									if(installedChunkData !== 0) installedChunks[chunkId] = undefined;
/******/ 									if(installedChunkData) {
/******/ 										var errorType = event && (event.type === 'load' ? 'missing' : event.type);
/******/ 										var realSrc = event && event.target && event.target.src;
/******/ 										error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realSrc + ')';
/******/ 										error.name = 'ChunkLoadError';
/******/ 										error.type = errorType;
/******/ 										error.request = realSrc;
/******/ 										installedChunkData[1](error);
/******/ 									}
/******/ 								}
/******/ 							};
/******/ 							__webpack_require__.l(url, loadingEnded, "chunk-" + chunkId, chunkId);
/******/ 						}
/******/ 					}
/******/ 				}
/******/ 		};
/******/ 		
/******/ 		// no prefetching
/******/ 		
/******/ 		// no preloaded
/******/ 		
/******/ 		// no HMR
/******/ 		
/******/ 		// no HMR manifest
/******/ 		
/******/ 		// no on chunks loaded
/******/ 		
/******/ 		// install a JSONP callback for chunk loading
/******/ 		var webpackJsonpCallback = (parentChunkLoadingFunction, data) => {
/******/ 			var [chunkIds, moreModules, runtime] = data;
/******/ 			// add "moreModules" to the modules object,
/******/ 			// then flag all "chunkIds" as loaded and fire callback
/******/ 			var moduleId, chunkId, i = 0;
/******/ 			if(chunkIds.some((id) => (installedChunks[id] !== 0))) {
/******/ 				for(moduleId in moreModules) {
/******/ 					if(__webpack_require__.o(moreModules, moduleId)) {
/******/ 						__webpack_require__.m[moduleId] = moreModules[moduleId];
/******/ 					}
/******/ 				}
/******/ 				if(runtime) var result = runtime(__webpack_require__);
/******/ 			}
/******/ 			if(parentChunkLoadingFunction) parentChunkLoadingFunction(data);
/******/ 			for(;i < chunkIds.length; i++) {
/******/ 				chunkId = chunkIds[i];
/******/ 				if(__webpack_require__.o(installedChunks, chunkId) && installedChunks[chunkId]) {
/******/ 					installedChunks[chunkId][0]();
/******/ 				}
/******/ 				installedChunks[chunkId] = 0;
/******/ 			}
/******/ 		
/******/ 		}
/******/ 		
/******/ 		var chunkLoadingGlobal = self["webpackChunk"] = self["webpackChunk"] || [];
/******/ 		chunkLoadingGlobal.forEach(webpackJsonpCallback.bind(null, 0));
/******/ 		chunkLoadingGlobal.push = webpackJsonpCallback.bind(null, chunkLoadingGlobal.push.bind(chunkLoadingGlobal));
/******/ 	})();
/******/ 	
/************************************************************************/
```

</details>

``` js
var __webpack_exports__ = {};
// This entry needs to be wrapped in an IIFE because it needs to be isolated against other modules in the chunk.
(() => {
/*!********************************!*\
  !*** ./example.js + 2 modules ***!
  \********************************/
/*! namespace exports */
/*! runtime requirements: __webpack_require__, __webpack_require__.e, __webpack_require__.* */
/*! ModuleConcatenation bailout: Cannot concat with ./node_modules/shared.js: Module ./node_modules/shared.js is referenced from different chunks by these modules: ./node_modules/c.js */

// EXTERNAL MODULE: ./node_modules/shared.js + 1 modules
var shared = __webpack_require__(1);
;// ./node_modules/a.js
// module a
var a = "a";


;// ./node_modules/b.js
// module b
function b_a() {
	return "b";
};

;// ./example.js



__webpack_require__.e(/*! import() */ "lazy_js").then(__webpack_require__.bind(__webpack_require__, /*! ./lazy */ 2)).then(function(lazy) {
	console.log(a, b_a(), shared.x, shared.y, lazy.c, lazy.d.a, lazy.x, lazy.y);
});

})();

/******/ })()
;
```

# dist/lazy_js.output.js

```javascript
(self["webpackChunk"] = self["webpackChunk"] || []).push([["lazy_js"],[
/* 0 */,
/* 1 */,
/* 2 */
/*!*****************************!*\
  !*** ./lazy.js + 2 modules ***!
  \*****************************/
/*! namespace exports */
/*! export c [provided] [used in main] [usage prevents renaming] -> ./node_modules/c.js .c */
/*! export d [provided] [only properties used in main] [usage prevents renaming] -> ./node_modules/d.js */
/*!   export a [provided] [used in main] [usage prevents renaming] */
/*! export x [provided] [used in main] [usage prevents renaming] -> ./node_modules/shared.js + 1 modules .x */
/*! export y [provided] [used in main] [usage prevents renaming] -> ./node_modules/shared2.js .y */
/*! runtime requirements: __webpack_exports__, __webpack_require__.d, __webpack_require__.r, __webpack_require__, __webpack_require__.* */
/*! ModuleConcatenation bailout: Cannot concat with ./node_modules/cjs.js: Module is not an ECMAScript module */
/*! ModuleConcatenation bailout: Cannot concat with ./node_modules/shared.js: Module ./node_modules/shared.js is not in the same chunk(s) (expected in chunk(s) unnamed chunk(s), module is in chunk(s) ) */
/***/ ((__unused_webpack_module, __webpack_exports__, __webpack_require__) => {

"use strict";

// EXPORTS
__webpack_require__.d(__webpack_exports__, {
  c: () => (/* reexport */ c),
  d: () => (/* reexport */ d_namespaceObject),
  x: () => (/* reexport */ shared.x),
  y: () => (/* reexport */ shared.y)
});

// NAMESPACE OBJECT: ./node_modules/d.js
var d_namespaceObject = {};
__webpack_require__.r(d_namespaceObject);
__webpack_require__.d(d_namespaceObject, {
  a: () => (a)
});

// EXTERNAL MODULE: ./node_modules/cjs.js
var cjs = __webpack_require__(3);
// EXTERNAL MODULE: ./node_modules/shared.js + 1 modules
var shared = __webpack_require__(1);
;// ./node_modules/c.js
// module c


var c = String.fromCharCode(cjs.c.charCodeAt(0) - 2);



;// ./node_modules/d.js
// module d
var a = "d";

;// ./lazy.js





/***/ }),
/* 3 */
/*!*****************************!*\
  !*** ./node_modules/cjs.js ***!
  \*****************************/
/*! default exports */
/*! export c [provided] [used in main] [could be renamed] */
/*! runtime requirements: __webpack_exports__ */
/*! ModuleConcatenation bailout: Module is not an ECMAScript module */
/***/ ((__unused_webpack_module, exports) => {

// module cjs (commonjs)
exports.c = "e";


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

Minimized

```javascript
(self.webpackChunk=self.webpackChunk||[]).push([["lazy_js"],{207(a,e,r){"use strict";r.d(e,{c:()=>C,d:()=>c,x:()=>s.x,y:()=>h.y});var c={};r.r(c),r.d(c,{a:()=>k});var d=r(330),s=r(331),h=r(453),C=String.fromCharCode(d.c.charCodeAt(0)-2),k="d"},330(a,e){e.c="e"}}]);
```

# Info

## Unoptimized

```
asset output.js 11.3 KiB [emitted] (name: main)
asset lazy_js.output.js 2.36 KiB [emitted]
chunk (runtime: main) lazy_js.output.js 263 bytes [rendered]
  > ./lazy ./example.js 4:0-16
  dependent modules 42 bytes [dependent] 1 module
  ./lazy.js + 2 modules 221 bytes [built] [code generated]
    [exports: c, d, x, y]
    [all exports used]
    import() ./lazy ./example.js + 2 modules ./example.js 4:0-16
chunk (runtime: main) output.js (main) 367 bytes (javascript) 5.48 KiB (runtime) [entry] [rendered]
  > ./example.js main
  runtime modules 5.48 KiB 8 modules
  dependent modules 100 bytes [dependent] 1 module
  ./example.js + 2 modules 267 bytes [built] [code generated]
    [no exports]
    [no exports used]
    entry ./example.js main
webpack X.X.X compiled successfully
```

## Production mode

```
asset output.js 2.08 KiB [emitted] [minimized] (name: main)
asset lazy_js.output.js 265 bytes [emitted] [minimized]
chunk (runtime: main) lazy_js.output.js 263 bytes [rendered]
  > ./lazy ./example.js 4:0-16
  dependent modules 42 bytes [dependent] 1 module
  ./lazy.js + 2 modules 221 bytes [built] [code generated]
    [exports: c, d, x, y]
    [all exports used]
    import() ./lazy ./example.js + 2 modules ./example.js 4:0-16
chunk (runtime: main) output.js (main) 367 bytes (javascript) 5.48 KiB (runtime) [entry] [rendered]
  > ./example.js main
  runtime modules 5.48 KiB 8 modules
  dependent modules 100 bytes [dependent] 2 modules
  ./example.js + 2 modules 267 bytes [built] [code generated]
    [no exports]
    [no exports used]
    entry ./example.js main
webpack X.X.X compiled successfully
```