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Minify the Output

So we’ve cued up our «dead code» to be dropped by using the and syntax, but we still need to drop it from the bundle. To do that, set the configuration option to .

webpack.config.js

With that squared away, we can run another and see if anything has changed.

Notice anything different about ? Clearly the whole bundle is now minified and mangled, but, if you look carefully, you won’t see the function included but will see a mangled version of the function (). With minification and tree shaking, our bundle is now a few bytes smaller! While that may not seem like much in this contrived example, tree shaking can yield a significant decrease in bundle size when working on larger applications with complex dependency trees.

Stats Object

The object that is passed as a second argument of the
callback, is a good source of information about the
code
compilation process. It includes:

  • Errors and Warnings (if any)
  • Timings
  • Module and Chunk information

The webpack CLI uses this information to display nicely formatted
output in your console.

This object exposes the following methods:

Can be used to check if there were errors while compiling. Returns or
.

Can be used to check if there were warnings while compiling. Returns or
.

Returns compilation information as a JSON object. can be either a
string (a preset) or an object for more granular control:

All available options and presets are described in the stats documentation.

Returns a formatted string of the compilation information (similar to
CLI output).

Options are the same as with one addition:

Here’s an example of usage:

Clarifying tree shaking and sideEffects

The and (more known as tree shaking) optimizations are two different things.

is much more effective since it allows to skip whole modules/files and the complete subtree.

relies on terser to detect side effects in statements. It is a difficult task in JavaScript and not as effective as straighforward flag. It also can’t skip subtree/dependencies since the spec says that side effects need to be evaluated. While exporting function works fine, React’s Higher Order Components (HOC) are problematic in this regard.

Let’s make an example:

The pre-bundled version looks like this:

When is unused you can effectively remove the which leaves all the remaining code. So the question is «Does this code have any side effects or can it be safely removed?». Difficult to say, especially because of this line . is called and the return value is also called. Are there any side effects when calling or ? Are there side effects when assigning (Setter?) or when reading (Getter?).

Terser actually tries to figure it out, but it doesn’t know for sure in many cases. This doesn’t mean that terser is not doing its job well because it can’t figure it out. It’s just too difficult to determine it reliably in a dynamic language like JavaScript.

But we can help terser by using the annotation. It flags a statement as side effect free. So a simple change would make it possible to tree-shake the code:

This would allow to remove this piece of code. But there are still questions with the imports which need to be included/evaluated because they could contain side effects.

To tackle this, we use the property in .

It’s similar to but on a module level instead of a statement level. It says ( property): «If no direct export from a module flagged with no-sideEffects is used, the bundler can skip evaluating the module for side effects.».

In the Shopify’s Polaris example, original modules look like this:

index.js

components/index.js

package.json

For this has the following implications:

  • include it: include the module, evaluate it and continue analysing dependencies
  • skip over: don’t include it, don’t evaluate it but continue analysing dependencies
  • exclude it: don’t include it, don’t evaluate it and don’t analyse dependencies

Specifically per matching resource(s):

  • : No direct export is used, but flagged with sideEffects -> include it
  • : No export is used, but flagged with sideEffects -> include it
  • : No export is used, not flagged with sideEffects -> exclude it
  • : No direct export is used, not flagged with sideEffects, but reexported exports are used -> skip over
  • : No export is used, not flagged with sideEffects -> exclude it. This also excluded all dependencies like even if they are flagged with sideEffects.
  • : Direct export is used, not flagged with sideEffects -> include it
  • : No export is used, but flagged with sideEffects -> include it

In this case only 4 modules are included into the bundle:

  • : pretty much empty

After this optimization, other optimizations can still apply. For example: and exports from are unused too. optimization will pick it up and terser may be able to drop some statements from the module.

Module Concatenation also applies. So that these 4 modules plus the entry module (and probably more dependencies) can be concatenated. has no code generated in the end.

Loading CSS

In order to a CSS file from within a JavaScript module, you need to install and add the style-loader and css-loader to your configuration:

webpack.config.js

This enables you to into the file that depends on that styling. Now, when that module is run, a tag with the stringified css will be inserted into the of your html file.

Let’s try it out by adding a new file to our project and import it in our :

project

src/style.css

src/index.js

Now run your build command:

Open up in your browser again and you should see that is now styled in red. To see what webpack did, inspect the page (don’t view the page source, as it won’t show you the result, because the tag is dynamically created by JavaScript) and look at the page’s head tags. It should contain the style block that we imported in .

Note that you can, and in most cases should, for better load times in production. On top of that, loaders exist for pretty much any flavor of CSS you can think of — postcss, sass, and less to name a few.

resolve

Configure how modules are resolved. For example, when calling in ES2015, the options can change where webpack goes to look for (see ).

webpack.config.js

Create aliases to or certain modules more easily. For example, to alias a bunch of commonly used folders:

webpack.config.js

Now, instead of using relative paths when importing like so:

you can use the alias:

A trailing can also be added to the given object’s keys to signify an exact match:

webpack.config.js

which would yield these results:

The following table explains other cases:

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

error

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

error

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

error

alias:

import ‘xyz’

import ‘xyz/file.js’

alias:

import ‘xyz’

import ‘xyz/file.js’

may resolve to another file if defined in the .

may resolve in too.

Specify a field, such as , to be parsed according to this specification.

webpack.config.js

(since webpack 3.1.0)

If unsafe cache is enabled, includes in the cache key. This option is taken into account by the module. Since webpack 3.1.0 context in resolve caching is ignored when resolve or resolveLoader plugins are provided. This addresses a performance regression.

The JSON files to use for descriptions.

webpack.config.js

If , it will not allow extension-less files. So by default works if has a extension, but with this enabled only will work.

webpack.config.js

Tells webpack whether to require to use an extension for modules (e.g. loaders).

webpack.config.js

Attempt to resolve these extensions in order.

webpack.config.js

which is what enables users to leave off the extension when importing:

When importing from an npm package, e.g. , this option will determine which fields in its are checked. The default values will vary based upon the specified in your webpack configuration.

When the property is set to , , or left unspecified:

webpack.config.js

For any other target (including ):

webpack.config.js

For example, consider an arbitrary library called with a that contains the following fields:

When we this will actually resolve to the file in the property. The property takes precedence because it’s the first item in . Meanwhile, a Node.js application bundled by webpack will first try to resolve using the file in the field.

The filename to be used while resolving directories.

webpack.config.js

Tell webpack what directories should be searched when resolving modules.

Absolute and relative paths can both be used, but be aware that they will behave a bit differently.

A relative path will be scanned similarly to how Node scans for , by looking through the current directory as well as its ancestors (i.e. , , and on).

With an absolute path, it will only search in the given directory.

webpack.config.js

If you want to add a directory to search in that takes precedence over :

webpack.config.js

Enable aggressive, but unsafe, caching of modules. Passing will cache everything.

webpack.config.js

A regular expression, or an array of regular expressions, can be used to test file paths and only cache certain modules. For example, to only cache utilities:

webpack.config.js

A list of additional resolve plugins which should be applied. It allows plugins such as .

webpack.config.js

Whether to resolve symlinks to their symlinked location.

When enabled, symlinked resources are resolved to their real path, not their symlinked location. Note that this may cause module resolution to fail when using tools that symlink packages (like ).

webpack.config.js

A function which decides whether a request should be cached or not. An object is passed to the function with and properties. It must return a boolean.

webpack.config.js

Добавляем Webpack

Для работы с Webpack необходимо его установить с помощью npm или yarn:

Теперь у вас подключён Webpack и доступна его командная строка. Но прежде, чем можно будет запустить сборку, файл должен импортировать код из . А экспортирует свои функции с помощью строки:

И чтобы мог использовать экспортированную функцию ,  добавляем строку:

Отлично, теперь все зависимости JavaScript связаны. Используем Webpack для создания приложения. Выполним следующую команду:

Сейчас вы должны увидеть новый файл , который содержит весь ваш код из и . Далее получаем с импортом вместо всех скриптов из , изменив код страницы следующим образом:

Добавление тестовых сценариев в сборку

Добавим несколько тестовых сценариев в файл . Для этого будем использовать Mocha, пакетный инструмент для написания тестов, и Chai в качестве нашей библиотеки установок. Выполните следующую команду:

Затем создайте новый каталог и новый файл , содержащий следующий фрагмент:

Теперь у вас есть тестовые сценарии для функций и , устанавливающие, что вычисляет формулу расстояния, а сортирует массивы координат с помощью формулы расстояния, используя наборы тестов Mocha и установки Chai. Довольно стандартная тестовая настройка.

Однако, если выполнить , будет ошибка “Код JavaScript недопустим”, потому что он содержит ключевое слово , которое Node в данный момент не поддерживает. Но что если обойти это ограничение, используя Webpack для управления зависимостями тестового кода?

Прим.: это можно легко исправить, просто используя вместо в тестовых файлах. Но тестовый код также будет проходить через процесс сборки, если вы тестируете JavaScript-код типа Flow, который использует аннотации, или веб-приложения Vue.js, которые используют файлы . Все они должны быть преобразованы в обычный JavaScript.

Список тестовых инструкций:

  1. Webpack строит граф зависимостей, начинающийся с тестовых файлов, а не с файлов приложения.
  2. Webpack создаёт файл JavaScript, содержащий весь тестовый код и его зависимости без ключевого слова .
  3. Выполняются тесты, запуская Mocha для этого JavaScript-файла.

Всё это будет выглядеть следующим образом:

Как можно увидеть, будут происходить две отдельные сборки. Одна из которых содержит код приложения в качестве точки входа и папку в качестве выходной директории, а другая — тестовые файлы в качестве точки входа и папку в качестве выходного каталога. Итак, давайте обновим конфигурационный файл, чтобы Webpack поддерживал вторую сборку:

Давайте разберёмся, что этот код делает. В строке 4 есть оператор , который  выполняется, если системная переменная имеет непустое значение. Так что, если вы выполните , то вам придётся вводить оператор , но это не потребуется, если просто выполнить .

Внутри оператора происходит выбор, какой JS-файл является точкой входа. Вместо уже установленного выходного каталога будет папка . А вместо точки входа — массив файлов, соответствующих глобальному выражению . Другими словами, это все файлы, которые находятся в каталоге и имеют путь, заканчивающийся на .

Новая точка входа и выходной путь передаются в объект , затем запускается Webpack для создания тестовой сборки. Конфигурация Webpack представляет собой обычный код JavaScript, поэтому можно использовать стандартную библиотеку Node и операторы для её настройки. Если выполнить , то можно увидеть каталог . А если запустить , то можно увидеть, как выполняются ваши тесты.

Наконец, в разделе вашего добавьте следующую строку:

Это означает, что когда вы выполняете , создаётся каталог (каталог сборки тестирования) с помощью Webpack, затем запускается Mocha для этой сборки, и, наконец, код удаляет каталог , поскольку он больше не используется (Commit 7).

Options

Name Type Description

Name

Type

Description

Unique ident for this plugin instance. (For advanced usage only, by default automatically generated)

Name

Type

Description

Name of the result file. May contain

,

and

Name

Type

Description

Extract from all additional chunks too (by default it extracts only from the initial chunk(s))

When using

and there are extracted chunks (from

) in the commons chunk,

must
be set to

Name

Type

Description

Disables the plugin

Name

Type

Description

Disables order check (useful for CSS Modules!),

by default

  • name of the chunk
  • number of the chunk
  • hash of the content of the extracted file
  • optionally you can configure

    • other s, e.g. , , ,
    • other s, e.g. , , , , , , , ,
    • and , the length of the hash in chars

Creates an extracting loader from an existing loader. Supports loaders of type .

Name Type Description

Name

Type

Description

//

Loader(s) that should be used for converting the resource to a CSS exporting module
(required)

Name

Type

Description

//

loader(e.g

) that should be used when the CSS is not extracted (i.e. in an additional chunk when

)

Name

Type

Description

Override the

setting for this loader

Multiple Instances

There is also an function on the instance. You should use this if you have more than one instance of .

Resolving

If you are finding that urls are not resolving properly when you run webpack. You can expand your loader functionality with options. The property allows your paths resolved without any changes.

parameter could be . It passes to process the format like and returns the real file name, . You can replace with then you will get the new path .

devServer.transportMode

This option allows us either to choose the current transport mode for client/server individually or to provide custom client/server implementation. This allows to specify how browser or other client communicates with the .

The current default mode is . This mode uses SockJS-node as a server, and SockJS-client on the client.

mode will become the default mode in the next major version. This mode uses ws as a server, and native WebSockets on the client.

Use mode:

To create a custom client implementation, create a class that extends .

Using path to , a custom WebSocket client implementation, along with the compatible server:

To create a custom server implementation, create a class that extends .

Using path to , a custom WebSocket server implementation, along with the compatible client:

Using class exported by , a custom WebSocket server implementation, along with the compatible client:

Using custom, compatible WebSocket client and server implementations:

Customized Loader

exposes a loader-builder utility that allows users to add custom handling
of Babel’s configuration for each file that it processes.

accepts a callback that will be called with the loader’s instance of
so that tooling can ensure that it using exactly the same
instance as the loader itself.

In cases where you want to customize without actually having a file to call , you
may also pass the option with a string pointing at a file that exports
your callback function.

Example

Given the loader’s options, split custom options out of ‘s
options.

Given Babel’s object, return the object that should
be passed to .

Given Babel’s result object, allow loaders to make additional tweaks to it.

Настройка Webpack с помощью файла webpack.config.js

То, что можно сделать с помощью команды , является стандартным режимом работы Webpack. Если выполнить , то он создаст граф зависимостей из входного файла и выдаст пакетный файл . Но задать расположение точек входа и выхода программы можно, настроив файл конфигурации. Поместите следующий код в файл с именем :

Теперь можно выполнить или сделать ту же сборку, что и раньше, без указания точки входа в программу в аргументах командной строки, т. к. теперь всё это есть в . Также это значит, что нужно обновить скрипт файла следующим образом:

Если в файле конфигурации изменить путь вывода на что-то вроде  , то при повторном выполнении команды пакетный файл будет помещён в  (Commit 5).

Файл конфигурации предназначен не только для настройки расположения входных и выходных файлов. Также можно настроить что именно Webpack делает, когда встречает файлы разных типов, используя специальные загрузчики, которые на самом деле являются JavaScript-программами, преобразующими ваш код. Например, в файле конфигурации может быть правило, определяющее, что, если Webpack встречает файл TypeScript в своём графе зависимостей, этот файл отправляется в загрузчик, который преобразует его из TypeScript в обычный JavaScript.

Загрузчик, который будет использоваться далее, — это Babel. Если вы не использовали его раньше, Babel — это инструмент, который берёт код JS, использующий современные функции, и преобразует его в эквивалент, совместимый со старыми версиями JavaScript. Это позволяет вашему приложению работать в старых браузерах или в браузерах, которые ещё не поддерживают некоторые новые функции JavaScript. В конце концов, некоторые ленивцы не обновляли свои браузеры с 2009 года. Некоторая часть написанного кода не будет работать в браузере 2009 года:

Здесь используется стрелочная функция и старые браузеры её не воспринимают. Поэтому используем загрузчик и отправим эту функцию в прошлое. Для начала выполним следующее:

Затем в файле добавим следующий код в :

Этот код добавит новое правило в ваш Webpack. Если в дереве зависимостей Webpack встречает файл, который заканчивается на (например, ), и этот файл отсутствует в папке (например, jQuery), то к этому файлу применяется данное правило.

Любой файл, который соответствует этому правилу, проходит через все загрузчики в блоке (в данном случае только через загрузчик babel). Таким образом, файлы и пройдут через загрузчик, что приведёт к удалению стрелочной функции в , а затем Webpack продолжит свой путь сборки. Тем временем, как только Webpack встречает jQuery, он просто загружает этот код как он есть без загрузчиков, поскольку jQuery находится в каталоге .

Теперь, если выполнить и посмотреть исходный код в , фрагмент, соответствующий вашей функции сортировки, использует ключевое слово , а не стрелочную функцию (Commit 6).

Подсвеченный код на верхнем изображении — это функция из до использования загрузчика, а подсвеченный код внизу — та же функция после добавления загрузчика

Обратите внимание на то, как выше мы используем стрелочную функцию, а ниже присутствует уже знакомое браузеру 2009 года ключевое слово

Теперь приложение готово к работе на устаревших браузерах. Чтобы этот код был поддерживаемым, следует написать несколько тестов для него.

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Usage

webpack documentation: Loaders

Within your webpack configuration object, you’ll need to add the babel-loader to the list of modules, like so:

Options

See the options.

You can pass options to the loader by using the property:

This loader also supports the following loader-specific option:

  • : Default . When set, the given directory will be used to cache the results of the loader. Future webpack builds will attempt to read from the cache to avoid needing to run the potentially expensive Babel recompilation process on each run. If the value is set to in options (), the loader will use the default cache directory in or fallback to the default OS temporary file directory if no folder could be found in any root directory.

  • : Default is a string composed by the ‘s version, the ‘s version, the contents of file if it exists, and the value of the environment variable with a fallback to the environment variable. This can be set to a custom value to force cache busting if the identifier changes.

  • : Default . When set, each Babel transform output will be compressed with Gzip. If you want to opt-out of cache compression, set it to — your project may benefit from this if it transpiles thousands of files.

  • : Default . The path of a module that exports a callback . Since you already have to make a new file to use this, it is recommended that you instead use to create a wrapper loader. Only use this if you must continue using directly, but still want to customize.

Defaults

Out of the box should work well for most users.

By default it only affects on-demand chunks, because changing initial chunks would affect the script tags the HTML file should include to run the project.

webpack will automatically split chunks based on these conditions:

  • New chunk can be shared OR modules are from the folder
  • New chunk would be bigger than 30kb (before min+gz)
  • Maximum number of parallel requests when loading chunks on demand would be lower or equal to 6
  • Maximum number of parallel requests at initial page load would be lower or equal to 4

When trying to fulfill the last two conditions, bigger chunks are preferred.

devServer

This set of options is picked up by webpack-dev-server and can be used to change its behavior in various ways. Here’s a simple example that gzips and serves everything from our directory in the project root:

webpack.config.js

When the server is started, there will be a message prior to the list of resolved modules:

that will give some background on where the server is located and what it’s serving.

If you’re using dev-server through the Node.js API, the options in will be ignored. Pass the options as a second parameter instead: . See here for an example of how to use webpack-dev-server through the Node.js API.

Conclusion

So, what we’ve learned is that in order to take advantage of tree shaking, you must…

  • Use ES2015 module syntax (i.e. and ).
  • Ensure no compilers transform your ES2015 module syntax into CommonJS modules (this is the default behavior of the popular Babel preset @babel/preset-env — see the for more details).
  • Add a property to your project’s file.
  • Use the configuration option to enable including minification and tree shaking.

You can imagine your application as a tree. The source code and libraries you actually use represent the green, living leaves of the tree. Dead code represents the brown, dead leaves of the tree that are consumed by autumn. In order to get rid of the dead leaves, you have to shake the tree, causing them to fall.

If you are interested in more ways to optimize your output, please jump to the next guide for details on building for production.

Options

Type:
Default:

Specifies an alternative loader to use when a target file’s size exceeds the
limit set in the option.

webpack.config.js

The fallback loader will receive the same configuration options as url-loader.

For example, to set the quality option of a responsive-loader above use:

webpack.config.js

Type:
Default:

The limit can be specified via loader options and defaults to no limit.

A or specifying the maximum size of a file in bytes. If the file size is
equal or greater than the limit
will be used (by default) and all query parameters are passed to it.
Using an alternative to is enabled via the option.

webpack.config.js

Enable or disable transform files into base64.

webpack.config.js

Type:
Default:

Sets the MIME type for the file to be transformed. If unspecified the file extensions will be used to lookup the MIME type.

webpack.config.js

Type:
Default:

By default, generates JS modules that use the ES modules syntax.
There are some cases in which using ES modules is beneficial, like in the case of module concatenation and tree shaking.

You can enable a CommonJS module syntax using:

webpack.config.js

Rule.use

can be an array of which are applied to modules. Each entry specifies a loader to be used.

Passing a string (i.e. ) is a shortcut to the loader property (i.e. ).

Loaders can be chained by passing multiple loaders, which will be applied from right to left (last to first configured).

webpack.config.js

can also be a function which receives the object argument describing the module being loaded, and must return an array of items.

The object parameter has the following fields:

  • : The current webpack compiler (can be undefined)
  • : The path to the module that is importing the module being loaded
  • : Always the path to the module being loaded
  • : The path to the module being loaded, it is usually equal to except when the resource name is overwritten via in request string

The same shortcut as an array can be used for the return value (i.e. ).

webpack.config.js

See for details.

Options

The plugin’s signature:

webpack.config.js

Patterns

Name Type Default Description

Name

Type

Default

Description

Glob or path from where we сopy files.

Name

Type

Default

Description

Output path.

Name

Type

Default

Description

A path that determines how to interpret the

path.

Name

Type

Default

Description

Determinate what is

option — directory, file or template.

Name

Type

Default

Description

Pattern for extracting elements to be used in

templates.

Name

Type

Default

Description

Overwrites files already in

(usually added by other plugins/loaders).

Name

Type

Default

Description

Globs to ignore files.

Name

Type

Default

Description

Removes all directory references and only copies file names.

Name

Type

Default

Description

Enable

caching. You can use

to invalidate the cache.

Name

Type

Default

Description

Allows to modify the file contents.

Name

Type

Default

Description

Allows to modify the writing path.

Name

Type

Default

Description

passed to the glob pattern matching library

Type:
Default:

Glob or path from where we сopy files.
Globs accept minimatch options.

webpack.config.js

Type:
Default:

Output path.

webpack.config.js

Type:
Default:

A path that determines how to interpret the path.

webpack.config.js

Type:
Default:

Determinate what is option — directory, file or template.
Sometimes it is hard to say what is , example .
If you want to copy files in directory you need use option.
We try to automatically determine the so you most likely do not need this option.

Name Type Default Description

Name

Type

Default

Description

If

is directory,

has no extension or ends in

Name

Type

Default

Description

If

has extension or

is file

Name

Type

Default

Description

If

contains

webpack.config.js

webpack.config.js

webpack.config.js

Type:
Default:

Pattern for extracting elements to be used in templates.

Defines a to match some parts of the file path.
These capture groups can be reused in the name property using placeholder.
Note that will be replaced by the entire path of the file,
whereas will contain the first capturing parenthesis of your
and so on…

webpack.config.js

Type:
Default:

Overwrites files already in (usually added by other plugins/loaders).

webpack.config.js

Type:
Default:

Globs to ignore files.

webpack.config.js

webpack.config.js

Type:
Default:

Removes all directory references and only copies file names.

webpack.config.js

Type:
Default:

Enable/disable caching. You can use to invalidate the cache.
Default path to cache directory: .

webpack.config.js

Type:
Default:

Allows to modify the file contents.

webpack.config.js

webpack.config.js

Type:
Default:

Allows to modify the writing path.

webpack.config.js

webpack.config.js

Type:
Default:

Allows to configute the glob pattern matching library used by the plugin.

webpack.config.js

Options

Name Type Default Description

Name

Type

Default

Description

Level of messages that the module will log

Name

Type

Default

Description

Array of globs to ignore (applied to

)

Name

Type

Default

Description

A path that determines how to interpret the

path, shared for all patterns

Name

Type

Default

Description

Copies files, regardless of modification when using watch or

. All files are copied on first build, regardless of this option

This property defines the level of messages that the module will log. Valid levels include:

  • (default)

Setting a log level means that all other levels below it will be visible in the
console. Setting will hide all console output. The module
leverages
for logging management, and more information can be found on its page.

webpack.config.js

Array of globs to ignore (applied to ).

webpack.config.js

A path that determines how to interpret the path, shared for all patterns.

webpack.config.js

Copies files, regardless of modification when using watch or . All files are copied on first build, regardless of this option.

webpack.config.js

Setup

The goals of development and production builds differ greatly. In development, we want strong source mapping and a localhost server with live reloading or hot module replacement. In production, our goals shift to a focus on minified bundles, lighter weight source maps, and optimized assets to improve load time. With this logical separation at hand, we typically recommend writing separate webpack configurations for each environment.

While we will separate the production and development specific bits out, note that we’ll still maintain a «common» configuration to keep things DRY. In order to merge these configurations together, we’ll use a utility called . With the «common» configuration in place, we won’t have to duplicate code within the environment-specific configurations.

Let’s start by installing and splitting out the bits we’ve already worked on in previous guides:

project

webpack.common.js

webpack.dev.js

webpack.prod.js

In , we now have setup our and configuration and we’ve included any plugins that are required for both environments. In , we’ve set to . Also, we’ve added the recommended for that environment (strong source mapping), as well as our simple configuration. Finally, in , is set to which loads , which was first introduced by the tree shaking guide.

Note the use of calls in the environment-specific configurations to include our common configuration in and . The tool offers a variety of advanced features for merging but for our use case we won’t need any of that.

Loading Data

Another useful asset that can be loaded is data, like JSON files, CSVs, TSVs, and XML. Support for JSON is actually built-in, similar to NodeJS, meaning will work by default. To import CSVs, TSVs, and XML you could use the csv-loader and xml-loader. Let’s handle loading all three:

webpack.config.js

Add some data files to your project:

project

src/data.xml

Now you can any one of those four types of data (JSON, CSV, TSV, XML) and the variable you import, will contain parsed JSON for easy consumption:

src/index.js

Re-run the command and open . If you look at the console in your developer tools, you should be able to see your imported data being logged to the console!

Loading Images

So now we’re pulling in our CSS, but what about our images like backgrounds and icons? Using the file-loader we can easily incorporate those in our system as well:

webpack.config.js

Now, when you , that image will be processed and added to your directory and the variable will contain the final url of that image after processing. When using the css-loader, as shown above, a similar process will occur for within your CSS. The loader will recognize this is a local file, and replace the path with the final path to the image in your directory. The html-loader handles in the same manner.

Let’s add an image to our project and see how this works, you can use any image you like:

project

src/index.js

src/style.css

Let’s create a new build and open up the index.html file again:

If all went well, you should now see your icon as a repeating background, as well as an element beside our text. If you inspect this element, you’ll see that the actual filename has changed to something like . This means webpack found our file in the folder and processed it!

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