Info

This example illustrates webpack's algorithm for automatic deduplication using optimization.splitChunks.

This example application contains 7 pages, each importing 1-3 modules from the node_modules folder (vendor libs) and 0-3 modules from the stuff folder (application modules). In reality, an application is probably more complex, but the same mechanisms apply.

The following configuration is used:

optimization.splitChunks.chunks: "all" - This opt-in into automatic splitting of initial chunks which is off by default
optimization.splitChunks.maxInitial/AsyncRequests: 20 - This opt-in into an HTTP2 optimized splitting mode by increasing the allowed amount of requests. The browser only supports 6 requests in parallel for HTTP1.1.

Interpreting the result

pageA.js the normal output files for the entrypoint pageA
vendors~pageD~pageE~pageF~pageG.js vendor libs shared by these pages extracted into a separate output file when larger than the threshold in size
vendors~pageA.js vendors only used by a single page but larger than the threshold in size
pageA~pageD~pageF.js application modules shared by these pages and larger than the threshold in size

Here, the threshold is 40 bytes but by default (in a real application) 30kb.

Some modules are intentionally duplicated, i. e. ./stuff/s4.js is shared by pageA and pageC, but it's the only shared module so no separate output file is created because it would be smaller than the threshold. A separate request (which comes with an overhead and worsen gzipping) is not worth the extra bytes.

Note: decreasing maxInitial/AsyncRequest will increase duplication further to reduce the number of requests. Duplication doesn't affect the initial page load, it only affects download size of navigations to other pages of the application.

webpack.config.js

"use strict";

module.exports = {
	// mode: "development" || "production",
	entry: {
		pageA: "./pages/a",
		pageB: "./pages/b",
		pageC: "./pages/c",
		pageD: "./pages/d",
		pageE: "./pages/e",
		pageF: "./pages/f",
		pageG: "./pages/g"
	},
	optimization: {
		splitChunks: {
			chunks: "all",
			maxInitialRequests: 20, // for HTTP2
			maxAsyncRequests: 20, // for HTTP2
			minSize: 40 // for example only: chosen to match 2 modules
			// omit minSize in real use case to use the default of 30kb
		}
	}
};

Production mode

assets by chunk 772 bytes (id hint: vendors)
  asset 454.js 164 bytes [emitted] [minimized] (id hint: vendors)
  asset 778.js 164 bytes [emitted] [minimized] (id hint: vendors)
  asset 122.js 111 bytes [emitted] [minimized] (id hint: vendors)
  asset 301.js 111 bytes [emitted] [minimized] (id hint: vendors)
  asset 811.js 111 bytes [emitted] [minimized] (id hint: vendors)
  asset 876.js 111 bytes [emitted] [minimized] (id hint: vendors)
asset pageB.js 1.25 KiB [emitted] [minimized] (name: pageB)
asset pageC.js 1.25 KiB [emitted] [minimized] (name: pageC)
asset pageA.js 1.17 KiB [emitted] [minimized] (name: pageA)
asset pageD.js 1.17 KiB [emitted] [minimized] (name: pageD)
asset pageF.js 1.17 KiB [emitted] [minimized] (name: pageF)
asset pageE.js 1.16 KiB [emitted] [minimized] (name: pageE)
asset pageG.js 1.14 KiB [emitted] [minimized] (name: pageG)
asset 554.js 139 bytes [emitted] [minimized]
chunk (runtime: pageA) 122.js (id hint: vendors) 43 bytes [initial] [rendered] split chunk (cache group: defaultVendors)
  > ./pages/a pageA
  ./node_modules/m3.js 43 bytes [built] [code generated]
chunk (runtime: pageG) pageG.js (pageG) 67 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/g pageG
  runtime modules 3.01 KiB 5 modules
  dependent modules 31 bytes [dependent] 1 module
  ./pages/g.js 36 bytes [built] [code generated]
chunk (runtime: pageB) pageB.js (pageB) 199 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/b pageB
  runtime modules 3.01 KiB 5 modules
  dependent modules 93 bytes [dependent] 3 modules
  ./pages/b.js 106 bytes [built] [code generated]
chunk (runtime: pageD, pageE, pageF, pageG) 301.js (id hint: vendors) 43 bytes [initial] [rendered] split chunk (cache group: defaultVendors)
  > ./pages/d pageD
  > ./pages/e pageE
  > ./pages/f pageF
  > ./pages/g pageG
  ./node_modules/m6.js 43 bytes [built] [code generated]
chunk (runtime: pageE) pageE.js (pageE) 93 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/e pageE
  runtime modules 3.01 KiB 5 modules
  dependent modules 31 bytes [dependent] 1 module
  ./pages/e.js 62 bytes [built] [code generated]
chunk (runtime: pageA) pageA.js (pageA) 137 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/a pageA
  runtime modules 3.01 KiB 5 modules
  dependent modules 31 bytes [dependent] 1 module
  ./pages/a.js 106 bytes [built] [code generated]
chunk (runtime: pageA, pageB, pageC) 454.js (id hint: vendors) 86 bytes [initial] [rendered] split chunk (cache group: defaultVendors)
  > ./pages/a pageA
  > ./pages/b pageB
  > ./pages/c pageC
  ./node_modules/m1.js 43 bytes [built] [code generated]
  ./node_modules/m2.js 43 bytes [built] [code generated]
chunk (runtime: pageA, pageD, pageF) 554.js 62 bytes [initial] [rendered] split chunk (cache group: default)
  > ./pages/a pageA
  > ./pages/d pageD
  > ./pages/f pageF
  ./stuff/s2.js 31 bytes [built] [code generated]
  ./stuff/s3.js 31 bytes [built] [code generated]
chunk (runtime: pageD, pageE, pageF) 778.js (id hint: vendors) 86 bytes [initial] [rendered] split chunk (cache group: defaultVendors)
  > ./pages/d pageD
  > ./pages/e pageE
  > ./pages/f pageF
  ./node_modules/m7.js 43 bytes [built] [code generated]
  ./node_modules/m8.js 43 bytes [built] [code generated]
chunk (runtime: pageB) 811.js (id hint: vendors) 43 bytes [initial] [rendered] split chunk (cache group: defaultVendors)
  > ./pages/b pageB
  ./node_modules/m4.js 43 bytes [built] [code generated]
chunk (runtime: pageC) 876.js (id hint: vendors) 43 bytes [initial] [rendered] split chunk (cache group: defaultVendors)
  > ./pages/c pageC
  ./node_modules/m5.js 43 bytes [built] [code generated]
chunk (runtime: pageD) pageD.js (pageD) 137 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/d pageD
  runtime modules 3.01 KiB 5 modules
  dependent modules 31 bytes [dependent] 1 module
  ./pages/d.js 106 bytes [built] [code generated]
chunk (runtime: pageC) pageC.js (pageC) 199 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/c pageC
  runtime modules 3.01 KiB 5 modules
  dependent modules 93 bytes [dependent] 3 modules
  ./pages/c.js 106 bytes [built] [code generated]
chunk (runtime: pageF) pageF.js (pageF) 137 bytes (javascript) 3.01 KiB (runtime) [entry] [rendered]
  > ./pages/f pageF
  runtime modules 3.01 KiB 5 modules
  dependent modules 31 bytes [dependent] 1 module
  ./pages/f.js 106 bytes [built] [code generated]
webpack X.X.X compiled successfully

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