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.
> 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](https://webpack.js.org/plugins/module-concatenation-plugin/) and [tree shaking](https://webpack.js.org/guides/tree-shaking/).
You can enable a CommonJS module syntax using:
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.css$/,
use: [
{
loader: 'file-loader',
options: {
esModule: false,
},
},
],
},
],
},
};
```
## Placeholders
Full information about placeholders you can find [here](https://github.com/webpack/loader-utils#interpolatename).
### `[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](https://en.wikipedia.org/wiki/Cryptographic_hash_function) 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**
```js
import png from './image.png';
```
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: 'dirname/[contenthash].[ext]',
},
},
],
},
],
},
};
```
Result:
```bash
# result
dirname/0dcbbaa701328ae351f.png
```
---
**file.js**
```js
import png from './image.png';
```
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: '[sha512:hash:base64:7].[ext]',
},
},
],
},
],
},
};
```
Result:
```bash
# result
gdyb21L.png
```
---
**file.js**
```js
import png from './path/to/file.png';
```
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.(png|jpe?g|gif)$/i,
use: [
{
loader: 'file-loader',
options: {
name: '[path][name].[ext]?[contenthash]',
},
},
],
},
],
},
};
```
Result:
```bash
# result
path/to/file.png?e43b20c069c4a01867c31e98cbce33c9
```
### CDN
The following examples show how to use `file-loader` for CDN uses query params.
**file.js**
```js
import png from './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__`.