Code Splitting

Bundling your JavaScript into a single file has one big downside: each time you change a minor detail in your application code, you must bust the browser cache. Even if you only change a single variable name, users will still need to re-download that generated file.

One solution is to isolate, or extract, your vendor libraries into their own file(s).

  • Application Code: app.js
  • Vendor Libraries: vendor.js
  • Manifest (webpack Runtime): manifest.js

This will result in a significantly smaller app.js file. Now, using the above example, if you change a variable name, only the application-specific JavaScript will need to be re-downloaded. The larger vendor libraries - vendor.js - may remain cached.

Basic Usage

// 1. Extract all node_modules vendor libraries into a vendor.js file.

// 2. Only extract the Vue and jQuery libraries (if used) into a vendor.js file.
mix.extract(['vue', 'jquery']);

// 3. Extract Vue and jQuery (if used) to custom-vendor-name.js.
mix.extract(['vue', 'jquery'], 'custom-vendor-name.js');

If you don't pass an array of npm libraries to the extract method, Mix will extract all imported libraries from your project's node_modules directory. This is a useful default; however, if you need to be explicit, pass an array of the specific libraries that should be extracted.

Once you compile your code - npx mix - you'll find three new files: app.js, vendor.js, and manifest.js. You may reference these at the bottom of your HTML.

<script src="/js/manifest.js"></script>
<script src="/js/vendor.js"></script>
<script src="/js/app.js"></script>

While it's true that we're now importing three scripts instead of one, the benefit is improved long-term caching of vendor code that rarely changes. Further, HTTP2 makes the cost of importing multiple scripts a non-issue.

Customize the Runtime Chunk Path

By default, the runtime chunk (manifest.js) is generated next to your JS assets.

However, the path can easily be customized, relative to the public path:

mix.options({ runtimeChunkPath: 'custom' });

// The `manifest.js` file will now be saved to `public/custom/manifest.js`

If you instead prefer the public path, use ..

mix.js('resources/app.js', 'public/js');
mix.options({ runtimeChunkPath: '.' });

// The `manifest.js` file will now be saved to `public/manifest.js`

Multiple Extractions

You may call mix.extract(['library1', 'library2']) multiple times with different arguments to extract different sets of libraries into separate files.

mix.extract(['vue', 'lodash-es'], 'vendor~utils-1.js');
mix.extract(['jquery', 'axios'], 'vendor~utils-2.js');

// `vendor~utils-1.js` will contain Vue and Lodash
// `vendor~utils-2.js` will contain jQuery and Axios

Fallback Extractions

A call to mix.extract() may be paired with one or more calls to mix.extract(['library1', 'library2'], 'file.js') and all libraries not extracted into specific files will be saved to vendor.js.

mix.extract(['vue', 'lodash-es'], 'vendor~utils-1.js');
mix.extract(['jquery', 'axios'], 'vendor~utils-2.js');

// `vendor~utils-1.js` will contain Vue and Lodash
// `vendor~utils-2.js` will contain jQuery and Axios
// `vendor.js` will contain all other used libraries from node_modules

Extractions Using Regular Expressions

It is now possible to match libraries by a regular expression. This is useful for libraries split into many modules/packages, like D3. To leverage this feature, pass an object to mix.extract().

  // If you don't specify a location, it defaults to `vendor.js`
  to: 'js/vendor-d3.js',

  // This can be an array of strings or a regular expression
  libraries: /d3|d3-[a-z0-9-]+/

Custom Extraction Tests

If you require more control over how modules are extracted, include a test function that receives the webpack module object and returns a boolean.

  to: 'js/vendor-core-js.js',
  test(mod) {
    return /core-js/.test(mod.nameForCondition());

The Manifest File

You might still be confused by that third manifest.js file. Webpack compiles with a small bit of run-time code to assist with its job. When not using mix.extract(), this code is invisible to you and lives inside your bundle file. However, if we need to split our code, that runtime code must "live" somewhere. As such, Laravel Mix will extract it to its own file.