webpack/examples/scope-hoisting/README.md

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 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 concatentation 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
var webpack = require("../../");

module.exports = {
	plugins: [
		new webpack.optimize.ModuleConcatenationPlugin()
	]
};
```




# js/output.js

<details><summary><code>/******/ (function(modules) { /* webpackBootstrap */ })</code></summary>

``` javascript
/******/ (function(modules) { // webpackBootstrap
/******/ 	// install a JSONP callback for chunk loading
/******/ 	var parentJsonpFunction = window["webpackJsonp"];
/******/ 	window["webpackJsonp"] = function webpackJsonpCallback(chunkIds, moreModules, executeModules) {
/******/ 		// add "moreModules" to the modules object,
/******/ 		// then flag all "chunkIds" as loaded and fire callback
/******/ 		var moduleId, chunkId, i = 0, resolves = [], result;
/******/ 		for(;i < chunkIds.length; i++) {
/******/ 			chunkId = chunkIds[i];
/******/ 			if(installedChunks[chunkId]) {
/******/ 				resolves.push(installedChunks[chunkId][0]);
/******/ 			}
/******/ 			installedChunks[chunkId] = 0;
/******/ 		}
/******/ 		for(moduleId in moreModules) {
/******/ 			if(Object.prototype.hasOwnProperty.call(moreModules, moduleId)) {
/******/ 				modules[moduleId] = moreModules[moduleId];
/******/ 			}
/******/ 		}
/******/ 		if(parentJsonpFunction) parentJsonpFunction(chunkIds, moreModules, executeModules);
/******/ 		while(resolves.length) {
/******/ 			resolves.shift()();
/******/ 		}
/******/
/******/ 	};
/******/
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/
/******/ 	// objects to store loaded and loading chunks
/******/ 	var installedChunks = {
/******/ 		1: 0
/******/ 	};
/******/
/******/ 	// 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;
/******/ 	}
/******/
/******/ 	// This file contains only the entry chunk.
/******/ 	// The chunk loading function for additional chunks
/******/ 	__webpack_require__.e = function requireEnsure(chunkId) {
/******/ 		var installedChunkData = installedChunks[chunkId];
/******/ 		if(installedChunkData === 0) {
/******/ 			return new Promise(function(resolve) { resolve(); });
/******/ 		}
/******/
/******/ 		// a Promise means "currently loading".
/******/ 		if(installedChunkData) {
/******/ 			return installedChunkData[2];
/******/ 		}
/******/
/******/ 		// setup Promise in chunk cache
/******/ 		var promise = new Promise(function(resolve, reject) {
/******/ 			installedChunkData = installedChunks[chunkId] = [resolve, reject];
/******/ 		});
/******/ 		installedChunkData[2] = promise;
/******/
/******/ 		// start chunk loading
/******/ 		var head = document.getElementsByTagName('head')[0];
/******/ 		var script = document.createElement('script');
/******/ 		script.type = 'text/javascript';
/******/ 		script.charset = 'utf-8';
/******/ 		script.async = true;
/******/ 		script.timeout = 120000;
/******/
/******/ 		if (__webpack_require__.nc) {
/******/ 			script.setAttribute("nonce", __webpack_require__.nc);
/******/ 		}
/******/ 		script.src = __webpack_require__.p + "" + chunkId + ".output.js";
/******/ 		var timeout = setTimeout(onScriptComplete, 120000);
/******/ 		script.onerror = script.onload = onScriptComplete;
/******/ 		function onScriptComplete() {
/******/ 			// avoid mem leaks in IE.
/******/ 			script.onerror = script.onload = null;
/******/ 			clearTimeout(timeout);
/******/ 			var chunk = installedChunks[chunkId];
/******/ 			if(chunk !== 0) {
/******/ 				if(chunk) {
/******/ 					chunk[1](new Error('Loading chunk ' + chunkId + ' failed.'));
/******/ 				}
/******/ 				installedChunks[chunkId] = undefined;
/******/ 			}
/******/ 		};
/******/ 		head.appendChild(script);
/******/
/******/ 		return promise;
/******/ 	};
/******/
/******/ 	// 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, {
/******/ 				configurable: false,
/******/ 				enumerable: true,
/******/ 				get: getter
/******/ 			});
/******/ 		}
/******/ 	};
/******/
/******/ 	// 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 = "js/";
/******/
/******/ 	// on error function for async loading
/******/ 	__webpack_require__.oe = function(err) { console.error(err); throw err; };
/******/
/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(__webpack_require__.s = 1);
/******/ })
/************************************************************************/
```

</details>

``` javascript
/******/ ([
/* 0 */
/*!********************************************!*\
  !*** ./node_modules/shared.js + 1 modules ***!
  \********************************************/
/*! exports provided: x, y */
/*! exports used: x, y */
/***/ (function(module, __webpack_exports__, __webpack_require__) {

"use strict";
Object.defineProperty(__webpack_exports__, "__esModule", { value: true });

// CONCATENATED MODULE: ./node_modules/shared2.js
// shared2 module
var y = "y";

// CONCATENATED MODULE: ./node_modules/shared.js
/* harmony export (binding) */ __webpack_require__.d(__webpack_exports__, "a", function() { return x; });
/* concated harmony reexport */__webpack_require__.d(__webpack_exports__, "b", function() { return y; });
// shared module
var x = "x";



/***/ }),
/* 1 */
/*!********************************!*\
  !*** ./example.js + 2 modules ***!
  \********************************/
/*! exports provided:  */
/*! all exports used */
/*! ModuleConcatenation bailout: Module is an entry point */
/***/ (function(module, __webpack_exports__, __webpack_require__) {

"use strict";
Object.defineProperty(__webpack_exports__, "__esModule", { value: true });

// EXTERNAL MODULE: ./node_modules/shared.js + 1 modules
var shared = __webpack_require__(0);

// CONCATENATED MODULE: ./node_modules/a.js
// module a
var a = "a";


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

// CONCATENATED MODULE: ./example.js



__webpack_require__.e/* import() */(0).then(__webpack_require__.bind(null, /*! ./lazy */ 3)).then(function(lazy) {
	console.log(a, b_a(), shared["a" /* x */], shared["b" /* y */], lazy.c, lazy.d.a, lazy.x, lazy.y);
});


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

# js/0.output.js

``` javascript
webpackJsonp([0],[
/* 0 */,
/* 1 */,
/* 2 */
/*!*****************************!*\
  !*** ./node_modules/cjs.js ***!
  \*****************************/
/*! no static exports found */
/*! exports used: c */
/*! ModuleConcatenation bailout: Module is not an ECMAScript module */
/***/ (function(module, exports) {

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


/***/ }),
/* 3 */
/*!*****************************!*\
  !*** ./lazy.js + 2 modules ***!
  \*****************************/
/*! exports provided: d, c, x, y */
/*! all exports used */
/*! ModuleConcatenation bailout: Module is referenced from these modules with unsupported syntax: ./example.js (referenced with import()) */
/***/ (function(module, __webpack_exports__, __webpack_require__) {

"use strict";
Object.defineProperty(__webpack_exports__, "__esModule", { value: true });
var d_namespaceObject = {};
__webpack_require__.d(d_namespaceObject, "a", function() { return a; });

// EXTERNAL MODULE: ./node_modules/cjs.js
var cjs = __webpack_require__(2);
var cjs_default = /*#__PURE__*/__webpack_require__.n(cjs);

// EXTERNAL MODULE: ./node_modules/shared.js + 1 modules
var shared = __webpack_require__(0);

// CONCATENATED MODULE: ./node_modules/c.js
// module c


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



// CONCATENATED MODULE: ./node_modules/d.js
// module d
var a = "d";

// CONCATENATED MODULE: ./lazy.js
/* concated harmony reexport */__webpack_require__.d(__webpack_exports__, "c", function() { return c; });
/* concated harmony reexport */__webpack_require__.d(__webpack_exports__, "x", function() { return shared["a" /* x */]; });
/* concated harmony reexport */__webpack_require__.d(__webpack_exports__, "y", function() { return shared["b" /* y */]; });
/* concated harmony reexport */__webpack_require__.d(__webpack_exports__, "d", function() { return d_namespaceObject; });





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

Minimized

``` javascript
webpackJsonp([0],[,,function(n,r){r.c="e"},function(n,r,t){"use strict";Object.defineProperty(r,"__esModule",{value:!0});var e={};t.d(e,"a",function(){return d});var u=t(2),c=t(0),o=String.fromCharCode(u.c.charCodeAt(0)-2),d="d";t.d(r,"c",function(){return o}),t.d(r,"x",function(){return c.a}),t.d(r,"y",function(){return c.b}),t.d(r,"d",function(){return e})}]);
```

# Info

## Uncompressed

```
Hash: 6596ce0a50ccbbaa89c6
Version: webpack 3.5.1
      Asset     Size  Chunks             Chunk Names
0.output.js   1.9 kB       0  [emitted]  
  output.js  7.39 kB       1  [emitted]  main
Entrypoint main = output.js
chunk    {0} 0.output.js 286 bytes {1} [rendered]
    > [] 4:0-16
    [3] ./lazy.js + 2 modules 242 bytes {0} [built]
        [exports: d, c, x, y]
        import() ./lazy [] ./example.js 4:0-16
     + 1 hidden module
chunk    {1} output.js (main) 390 bytes [entry] [rendered]
    > main [] 
    [0] ./node_modules/shared.js + 1 modules 105 bytes {1} [built]
        [exports: x, y]
        [only some exports used: x, y]
        harmony import shared [1] ./example.js + 2 modules 3:0-23
        harmony import shared [3] ./lazy.js + 2 modules 6:0-30
    [1] ./example.js + 2 modules 285 bytes {1} [built]
        [no exports]
```

## Minimized (uglify-js, no zip)

```
Hash: 6596ce0a50ccbbaa89c6
Version: webpack 3.5.1
      Asset       Size  Chunks             Chunk Names
0.output.js  364 bytes       0  [emitted]  
  output.js    1.66 kB       1  [emitted]  main
Entrypoint main = output.js
chunk    {0} 0.output.js 286 bytes {1} [rendered]
    > [] 4:0-16
    [3] ./lazy.js + 2 modules 242 bytes {0} [built]
        [exports: d, c, x, y]
        import() ./lazy [] ./example.js 4:0-16
     + 1 hidden module
chunk    {1} output.js (main) 390 bytes [entry] [rendered]
    > main [] 
    [0] ./node_modules/shared.js + 1 modules 105 bytes {1} [built]
        [exports: x, y]
        [only some exports used: x, y]
        harmony import shared [1] ./example.js + 2 modules 3:0-23
        harmony import shared [3] ./lazy.js + 2 modules 6:0-30
    [1] ./example.js + 2 modules 285 bytes {1} [built]
        [no exports]
```