Output

The top-level output key contains set of options instructing webpack on how and where it should output your bundles, assets and anything else you bundle or load with webpack.

output.chunkFilename

string

This option determines the name of on-demand loaded chunk files. See output.filename option for details on the possible values.

Note that these filenames need to be generated at runtime to send the requests for chunks. Because of this, placeholders like [name] and [chunkhash] need to add a mapping from chunk id to placeholder value to the output bundle with the webpack runtime. This increases the size and may invalidate the bundle when placeholder value for any chunk changes.

By default [id].js is used or a value inferred from output.filename ([name] is replaced with [id] or [id]. is prepended).

output.crossOriginLoading

boolean string

Only used when target is web, which uses JSONP for loading on-demand chunks, by adding script tags.

Enable cross-origin loading of chunks. The following values are accepted...

crossOriginLoading: false - Disable cross-origin loading (default)

crossOriginLoading: "anonymous" - Enable cross-origin loading without credentials

crossOriginLoading: "use-credentials" - Enable cross-origin loading with credentials

output.devtoolFallbackModuleFilenameTemplate

string | function(info)

A fallback used when the template string or function above yields duplicates.

See output.devtoolModuleFilenameTemplate.

output.devtoolLineToLine

boolean | object

(Deprecated: Not really used, not really usable, write an issue if you have a different opinion)

Enables line to line mapping for all or some modules. This produces a simple source map where each line of the generated source is mapped to the same line of the original source. This is a performance optimization and should only be used if all input lines match generated lines.

Pass a boolean to enable or disable this feature for all modules (defaults to false). An object with test, include, exclude is also allowed. For example, to enable this feature for all javascript files within a certain directory:

devtoolLineToLine: { test: /\.js$/, include: 'src/utilities' }

output.devtoolModuleFilenameTemplate

string | function(info)

This option is only used when devtool uses an options which requires module names.

Customize the names used in each source map's sources array. This can be done by passing a template string or function. For example, when using devtool: 'eval', this is the default:

devtoolModuleFilenameTemplate: "webpack:///[resource-path]?[loaders]"

The following substitutions are available in template strings (via webpack's internal ModuleFilenameHelpers):

Template
Description
Template
[absolute-resource-path]
Description
The absolute filename
Template
[all-loaders]
Description
Automatic and explicit loaders and params up to the name of the first loader
Template
[hash]
Description
The hash of the module identifier
Template
[id]
Description
The module identifier
Template
[loaders]
Description
Explicit loaders and params up to the name of the first loader
Template
[resource]
Description
The path used to resolve the file and any query params used on the first loader
Template
[resource-path]
Description
The path used to resolve the file without any query params

When using a function, the same options are available camel-cased via the info parameter:

devtoolModuleFilenameTemplate: info => {
  return `webpack:///${info.resourcePath}?${info.loaders}`
}

If multiple modules would result in the same name, output.devtoolFallbackModuleFilenameTemplate is used instead for these modules.

output.hashFunction

The hashing algorithm to use, defaults to 'md5'. All functions from Node.JS' crypto.createHash are supported.

output.hashDigest

The hashing algorithm to use, defaults to 'hex'. All functions from Node.JS' hash.digest are supported.

output.hashDigestLength

The prefix length of the hash digest to use, defaults to 20.

output.hashSalt

An optional salt to update the hash via Node.JS' hash.update.

output.filename

string

This option determines the name of each output bundle. The bundle is written to the directory specified by the output.path option.

For a single entry point, this can be a static name.

filename: "bundle.js"

However, when creating multiple bundles via more than one entry point, code splitting, or various plugins, you should use one of the following substitutions to give each bundle a unique name...

Using entry name:

filename: "[name].bundle.js"

Using internal chunk id:

filename: "[id].bundle.js"

Using the unique hash generated for every build:

filename: "[name].[hash].bundle.js"

Using hashes based on each chunks' content:

filename: "[chunkhash].bundle.js"

Make sure the read the Caching guide for details. There are more steps involved than just setting this option.

The default value is "[name].js".

Note this option is called filename but you are still allowed to something like "js/[name]/bundle.js" to create a folder structure.

Note this options does not affect output files for on-demand-loaded chunks. For these files the output.chunkFilename option is used. It also doesn't affect files created by loaders. For these files see loader options.

The following substitutions are available in template strings (via webpack's internal TemplatedPathPlugin):

Template
Description
Template
[hash]
Description
The hash of the module identifier
Template
[chunkhash]
Description
The hash of the chunk content
Template
[name]
Description
The module name
Template
[id]
Description
The module identifier
Template
[file]
Description
The module filename
Template
[filebase]
Description
The module basename
Template
[query]
Description
The module query, i.e., the string following ? in the filename

The lengths of [hash] and [chunkhash] can be specified using [hash:16] (defaults to 20). Alternatively, specify output.hashDigestLength to configure the length globally.

When using the ExtractTextWebpackPlugin, use [contenthash] to obtain a hash of the extracted file (neither [hash] nor [chunkhash] work).

output.hotUpdateChunkFilename

string

Customize the filenames of hot update chunks. See output.filename option for details on the possible values.

The only placeholders allowed here are [id] and [hash], the default being:

hotUpdateChunkFilename: "[id].[hash].hot-update.js"

Here is no need to change it.

output.hotUpdateFunction

function

Only used when target is web, which uses JSONP for loading hot updates.

A JSONP function used to asynchronously load hot-update chunks.

For details see output.jsonpFunction.

output.hotUpdateMainFilename

string

Customize the main hot update filename. See output.filename option for details on the possible values.

[hash] is the only available placeholder, the default being:

hotUpdateMainFilename: "[hash].hot-update.json"

Here is no need to change it.

output.jsonpFunction

string

Only used when target is web, which uses JSONP for loading on-demand chunks.

A JSONP function name used to asynchronously load chunks or join multiple initial chunks (CommonsChunkPlugin, AggressiveSplittingPlugin).

This needs to be changed if multiple webpack runtimes (from different compilation) are used on the same webpage.

If using the output.library option, the library name is automatically appended.

output.library

string

Read the library guide for details.

Use library, and libraryTarget below, when writing a JavaScript library that should export values, which can be used by other code depending on it. Pass a string with the name of the library:

library: "MyLibrary"

The name is used depending on the value of the output.libraryTarget options.

Note that output.libraryTarget defaults to var. This means if only output.library is used it is exported as variable declaration (when used as script tag it's available in the global scope after execution).

output.libraryTarget

string

Default: "var"

Read the library guide for details.

Configure how the library will be exposed. Any one of the following options can be used.

To give your library a name, set the output.library config to it (the examples assume library: "MyLibrary")

The following options are supported:

libraryTarget: "var" - (default) When your library is loaded, the return value of your entry point will be assigned to a variable:

var MyLibrary = _entry_return_;

// your users will use your library like:
MyLibrary.doSomething();
Not specifying a output.library will cancel this "var" configuration.

libraryTarget: "this" - When your library is loaded, the return value of your entry point will be assigned to this, the meaning of this is up to you:

this["MyLibrary"] = _entry_return_;

// your users will use your library like:
this.MyLibrary.doSomething();
MyLibrary.doSomething(); //if this is window

libraryTarget: "window" - When your library is loaded, the return value of your entry point will be part window object.

 window["MyLibrary"] = _entry_return_;

//your users will use your library like:
window.MyLibrary.doSomething();

libraryTarget: "global" - When your library is loaded, the return value of your entry point will be part global object.

 global["MyLibrary"] = _entry_return_;

//your users will use your library like:
global.MyLibrary.doSomething();

libraryTarget: "commonjs" - When your library is loaded, the return value of your entry point will be part of the exports object. As the name implies, this is used in CommonJS environments:

exports["MyLibrary"] = _entry_return_;

//your users will use your library like:
require("MyLibrary").doSomething();

libraryTarget: "commonjs2" - When your library is loaded, the return value of your entry point will be part of the exports object. As the name implies, this is used in CommonJS environments:

module.exports = _entry_return_;

//your users will use your library like:
require("MyLibrary").doSomething();

Wondering the difference between CommonJS and CommonJS2? Check this out (they are pretty much the same).

libraryTarget: "commonjs-module" - Expose it using the module.exports object (output.library is ignored), __esModule is defined (it's threaded as ES2015 Module in interop mode)

libraryTarget: "amd" - In this case webpack will make your library an AMD module.

But there is a very important pre-requisite, your entry chunk must be defined with the define property, if not, webpack will create the AMD module, but without dependencies. The output will be something like this:

define([], function() {
    //what this module returns is what your entry chunk returns
});

But if you download this script, you may get an error: define is not defined, it’s ok! If you are distributing your library with AMD, then your users need to use RequireJS to load it.

Now that you have RequireJS loaded, you can load your library.

But, require([ _what?_ ])?

output.library!

output: {
    library: "MyLibrary",
    libraryTarget: "amd"
}

So your module will be like:

define("MyLibrary", [], function() {
    //what this module returns is what your entry chunk returns
});

And you can use it like this:

// And then your users will be able to do:
require(["MyLibrary"], function(MyLibrary){
    MyLibrary.doSomething();
});

libraryTarget: "umd" - This is a way for your library to work with all the module definitions (and where aren't modules at all). It will work with CommonJS, AMD and as global variable. You can check the UMD Repository to know more about it.

In this case, you need the library property to name your module:

output: {
    library: "MyLibrary",
    libraryTarget: "umd"
}

And finally the output is:

(function webpackUniversalModuleDefinition(root, factory) {
    if(typeof exports === 'object' && typeof module === 'object')
        module.exports = factory();
    else if(typeof define === 'function' && define.amd)
        define("MyLibrary", [], factory);
    else if(typeof exports === 'object')
        exports["MyLibrary"] = factory();
    else
        root["MyLibrary"] = factory();
})(this, function() {
    //what this module returns is what your entry chunk returns
});

Module proof library.

libraryTarget: "assign" - Here webpack will blindly generate an implied global.

 MyLibrary = _entry_return_;

Be aware that if MyLibrary isn't defined earlier your library will be set in global scope.

libraryTarget: "jsonp" - This will wrap the return value of your entry point into a jsonp wrapper.

 MyLibrary(_entry_return_);

The dependencies for your library will be defined by the externals config.

output.path

string

The output directory as an absolute path.

path: path.resolve(__dirname, 'dist/assets')

Note that [hash] in this parameter will be replaced with an hash of the compilation. See the Caching guide for details.

output.pathinfo

boolean

Tell webpack to include comments in bundles with information about the contained modules. This option defaults to false and should not be used in production, but it's very useful in development when reading the generated code.

pathinfo: true

Note it also adds some info about tree shaking to the generated bundle.

output.publicPath

string

This is an important option when using on-demand-loading or loading external resources like images, files, etc. If an incorrect value is specified you'll receive 404 errors while loading these resources.

This option specifies the public URL of the output directory when referenced in a browser. A relative URL is resolved relative to the HTML page (or <base> tag). Server-relative URLs, protocol-relative URLs or absolute URLs are also possible and sometimes required, i. e. when hosting assets on a CDN.

The value of the option is prefixed to every URL created by the runtime or loaders. Because of this the value of this option ends with / in most cases.

The default value is an empty string "".

Simple rule: The URL of your output.path from the view of the HTML page.

path: path.resolve(__dirname, "public/assets"),
publicPath: "https://cdn.example.com/assets/"

For this configuration:

publicPath: "/assets/",
chunkFilename: "[id].chunk.js"

A request to a chunk will look like /assets/4.chunk.js.

A loader outputting HTML might emit something like this:

<link href="/assets/spinner.gif" />

or when loading an image in CSS:

background-image: url(/assets/spinner.gif);

The webpack-dev-server also takes a hint from publicPath, using it to determine where to serve the output files from.

Note that [hash] in this parameter will be replaced with an hash of the compilation. See the Caching guide for details.

Examples:

publicPath: "https://cdn.example.com/assets/", // CDN (always HTTPS)
publicPath: "//cdn.example.com/assets/", // CDN (same protocol)
publicPath: "/assets/", // server-relative
publicPath: "assets/", // relative to HTML page
publicPath: "../assets/", // relative to HTML page
publicPath: "", // relative to HTML page (same directory)

output.sourceMapFilename

string

This option is only used when devtool uses a SourceMap option which writes an output file.

Configure how source maps are named. By default "[file].map" is used.

Technically, the [name], [id], [hash] and [chunkhash] placeholders can be used, if generating a SourceMap for chunks. In addition to that, the [file] placeholder is replaced with the filename of the original file. It's recommended to only use the [file] placeholder, as the other placeholders won't work when generating SourceMaps for non-chunk files. Best leave the default.

output.sourcePrefix

string

Change the prefix for each line in the output bundles.

sourcePrefix: "\t"

Note by default an empty string is used. Using some kind of indentation makes bundles look more pretty, but will cause issues with multi-line strings.

There is no need to change it.

output.strictModuleExceptionHandling

boolean

Tell webpack to remove a module from the module instance cache (require.cache) if it throws an exception when it is required.

It defaults to false for performance reasons.

When set to false, the module is not removed from cache, which results in the exception getting thrown only on the first require call (making it incompatible with node.js).

For instance, consider module.js:

throw new Error("error");

With strictModuleExceptionHandling set to false, only the first require throws an exception:

// with strictModuleExceptionHandling = false
require("module") // <- throws
require("module") // <- doesn't throw

Instead, with strictModuleExceptionHandling set to true, all requires of this module throw an exception:

// with strictModuleExceptionHandling = true
require("module") // <- throws
require("module") // <- also throw

output.umdNamedDefine

boolean

When using libraryTarget: "umd", setting:

umdNamedDefine: true

will name the AMD module of the UMD build. Otherwise an anonymous define is used.


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