JarCasting
file-loader
The file-loader resolves import/require() on a file into a url and emits the file into the output directory.
Getting Started
To begin, you'll need to install file-loader:
$ npm install file-loader --save-dev
Import (or require) the target file(s) in one of the bundle's files:
file.js
import img from './file.png';
Then add the loader to your webpack config. For example:
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
},
],
},
],
},
};
And run webpack via your preferred method. This will emit file.png as a file in the output directory (with the specified naming convention, if options are specified to do so) and returns the public URI of the file.
ℹ️ By default the filename of the resulting file is the hash of the file's contents with the original extension of the required resource.
Options
name
Type: String|Function Default: '[contenthash].[ext]'
Specifies a custom filename template for the target file(s) using the query parameter name. For example, to emit a file from your context directory into the output directory retaining the full directory structure, you might use:
String
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
loader: 'file-loader',
options: {
name: '[path][name].[ext]',
},
},
],
},
};
Function
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
loader: 'file-loader',
options: {
name(resourcePath, resourceQuery) {
// `resourcePath` - `/absolute/path/to/file.js`
// `resourceQuery` - `?foo=bar`
if (process.env.NODE_ENV === 'development') {
return '[path][name].[ext]';
}
return '[contenthash].[ext]';
},
},
},
],
},
};
ℹ️ By default the path and name you specify will output the file in that same directory, and will also use the same URI path to access the file.
outputPath
Type: String|Function Default: undefined
Specify a filesystem path where the target file(s) will be placed.
String
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
loader: 'file-loader',
options: {
outputPath: 'images',
},
},
],
},
};
Function
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
loader: 'file-loader',
options: {
outputPath: (url, resourcePath, context) => {
// `resourcePath` is original absolute path to asset
// `context` is directory where stored asset (`rootContext`) or `context` option
// To get relative path you can use
// const relativePath = path.relative(context, resourcePath);
if (/my-custom-image\.png/.test(resourcePath)) {
return `other_output_path/${url}`;
}
if (/images/.test(context)) {
return `image_output_path/${url}`;
}
return `output_path/${url}`;
},
},
},
],
},
};
publicPath
Type: String|Function Default: __webpack_public_path__+outputPath
Specifies a custom public path for the target file(s).
String
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
loader: 'file-loader',
options: {
publicPath: 'assets',
},
},
],
},
};
Function
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
loader: 'file-loader',
options: {
publicPath: (url, resourcePath, context) => {
// `resourcePath` is original absolute path to asset
// `context` is directory where stored asset (`rootContext`) or `context` option
// To get relative path you can use
// const relativePath = path.relative(context, resourcePath);
if (/my-custom-image\.png/.test(resourcePath)) {
return `other_public_path/${url}`;
}
if (/images/.test(context)) {
return `image_output_path/${url}`;
}
return `public_path/${url}`;
},
},
},
],
},
};
postTransformPublicPath
Type: Function Default: undefined
Specifies a custom function to post-process the generated public path. This can be used to prepend or append dynamic global variables that are only available at runtime, like __webpack_public_path__. This would not be possible with just publicPath, since it stringifies the values.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpg|gif)$/i,
loader: 'file-loader',
options: {
publicPath: '/some/path/',
postTransformPublicPath: (p) => `__webpack_public_path__ + ${p}`,
},
},
],
},
};
context
Type: String Default: context
Specifies a custom file context.
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
context: 'project',
},
},
],
},
],
},
};
emitFile
Type: Boolean Default: true
If true, emits a file (writes a file to the filesystem). If false, the loader will return a public URI but will not emit the file. It is often useful to disable this option for server-side packages.
file.js
// bundle file
import img from './file.png';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/i,
use: [
{
loader: 'file-loader',
options: {
emitFile: false,
},
},
],
},
],
},
};
regExp
Type: RegExp Default: undefined
Specifies a Regular Expression to one or many parts of the target file path. The capture groups can be reused in the name property using [N] placeholder.
file.js
import img from './customer01/file.png';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
regExp: /\/([a-z0-9]+)\/[a-z0-9]+\.png$/i,
name: '[1]-[name].[ext]',
},
},
],
},
],
},
};
ℹ️ If[0]is used, it will be replaced by the entire tested string, whereas[1]will contain the first capturing parenthesis of your regex and so on...
esModule
Type: Boolean Default: true
By default, file-loader generates JS modules that use the ES modules syntax. There are some cases in which using ES modules is beneficial, like in the case of module concatenation and tree shaking.
You can enable a CommonJS module syntax using:
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: [
{
loader: 'file-loader',
options: {
esModule: false,
},
},
],
},
],
},
};
Placeholders
Full information about placeholders you can find here.
[ext]
Type: String Default: file.extname
The file extension of the target file/resource.
[name]
Type: String Default: file.basename
The basename of the file/resource.
[path]
Type: String Default: file.directory
The path of the resource relative to the webpack/config context.
[folder]
Type: String Default: file.folder
The folder of the resource is in.
[query]
Type: String Default: file.query
The query of the resource, i.e. ?foo=bar.
[emoji]
Type: String Default: undefined
A random emoji representation of content.
[emoji:<length>]
Type: String Default: undefined
Same as above, but with a customizable number of emojis
[hash]
Type: String Default: md4
Specifies the hash method to use for hashing the file content.
[contenthash]
Type: String Default: md4
Specifies the hash method to use for hashing the file content.
[<hashType>:hash:<digestType>:<length>]
Type: String
The hash of options.content (Buffer) (by default it's the hex digest of the hash).
digestType
Type: String Default: 'hex'
The digest that the hash function should use. Valid values include: base26, base32, base36, base49, base52, base58, base62, base64, and hex.
hashType
Type: String Default: 'md4'
The type of hash that the has function should use. Valid values include: md4, md5, sha1, sha256, and sha512.
length
Type: Number Default: undefined
Users may also specify a length for the computed hash.
[N]
Type: String Default: undefined
The n-th match obtained from matching the current file name against the regExp.
Examples
Names
The following examples show how one might use file-loader and what the result would be.
file.js
import png from './image.png';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: 'dirname/[contenthash].[ext]',
},
},
],
},
],
},
};
Result:
# result
dirname/0dcbbaa701328ae351f.png
file.js
import png from './image.png';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: '[sha512:hash:base64:7].[ext]',
},
},
],
},
],
},
};
Result:
# result
gdyb21L.png
file.js
import png from './path/to/file.png';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: '[path][name].[ext]?[contenthash]',
},
},
],
},
],
},
};
Result:
# result
path/to/file.png?e43b20c069c4a01867c31e98cbce33c9
CDN
The following examples show how to use file-loader for CDN uses query params.
file.js
import png from './directory/image.png?width=300&height=300';
webpack.config.js
module.exports = {
output: {
publicPath: 'https://cdn.example.com/',
},
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: '[path][name].[ext][query]',
},
},
],
},
],
},
};
Result:
# result
https://cdn.example.com/directory/image.png?width=300&height=300
Dynamic public path depending on environment variable at run time
An application might want to configure different CDN hosts depending on an environment variable that is only available when running the application. This can be an advantage, as only one build of the application is necessary, which behaves differently depending on environment variables of the deployment environment. Since file-loader is applied when compiling the application, and not when running it, the environment variable cannot be used in the file-loader configuration. A way around this is setting the __webpack_public_path__ to the desired CDN host depending on the environment variable at the entrypoint of the application. The option postTransformPublicPath can be used to configure a custom path depending on a variable like __webpack_public_path__.
main.js
const assetPrefixForNamespace = (namespace) => {
switch (namespace) {
case 'prod':
return 'https://cache.myserver.net/web';
case 'uat':
return 'https://cache-uat.myserver.net/web';
case 'st':
return 'https://cache-st.myserver.net/web';
case 'dev':
return 'https://cache-dev.myserver.net/web';
default:
return '';
}
};
const namespace = process.env.NAMESPACE;
__webpack_public_path__ = `${assetPrefixForNamespace(namespace)}/`;
file.js
import png from './image.png';
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpg|gif)$/i,
loader: 'file-loader',
options: {
name: '[name].[contenthash].[ext]',
outputPath: 'static/assets/',
publicPath: 'static/assets/',
postTransformPublicPath: (p) => `__webpack_public_path__ + ${p}`,
},
},
],
},
};
Result when run with NAMESPACE=prod env variable:
# result
https://cache.myserver.net/web/static/assets/image.somehash.png
Result when run with NAMESPACE=dev env variable:
# result
https://cache-dev.myserver.net/web/static/assets/image.somehash.png
Contributing
Please take a moment to read our contributing guidelines if you haven't yet done so.
