There are two main benefits in enabling it. First it is faster since no copying is required and second is that assets
will always be up to date with source files.
Compressing and combining assets
--------------------------------
To improve application performance you can compress and then combine several CSS or JS files into lesser number of files
therefore reducing number of HTTP requests and overall download size needed to load a web page. Yii provides a console
command that allows you to do both.
### Preparing configuration
In order to use `asset` command you should prepare a configuration first. A template for it can be generated using
```
yii asset/template /path/to/myapp/config.php
```
The template itself looks like the following:
```php
<?php
/**
* Configuration file for the "yii asset" console command.
* Note that in the console environment, some path aliases like '@webroot' and '@web' may not exist.
* Please define these missing path aliases.
*/
return[
// The list of asset bundles to compress:
'bundles'=>[
// 'yii\web\YiiAsset',
// 'yii\web\JqueryAsset',
],
// Asset bundle for compression output:
'targets'=>[
'app\config\AllAsset'=>[
'basePath'=>'path/to/web',
'baseUrl'=>'',
'js'=>'js/all-{ts}.js',
'css'=>'css/all-{ts}.css',
],
],
// Asset manager configuration:
'assetManager'=>[
'basePath'=>__DIR__,
'baseUrl'=>'',
],
];
```
In the above keys are `properties` of `AssetController`. `bundles` list contains bundles that should be compressed. These are typically what's used by application.
`targets` contains a list of bundles that define how resulting files will be written. In our case we're writing
everything to `path/to/web` that can be accessed like `http://example.com/` i.e. it is website root directory.
> Note: in the console environment some path aliases like '@webroot' and '@web' may not exist,
so corresponding paths inside the configuration should be specified directly.
JavaScript files are combined, compressed and written to `js/all-{ts}.js` where {ts} is replaced with current UNIX
timestamp.
### Providing compression tools
The command relies on external compression tools that are not bundled with Yii so you need to provide CSS and JS
compressors which are correspondingly specified via `cssCompressor` and `jsCompression` properties. If compressor is
specified as a string it is treated as a shell command template which should contain two placeholders: `{from}` that
is replaced by source file name and `{to}` that is replaced by output file name. Another way to specify compressor is
to use any valid PHP callback.
By default for JavaScript compression Yii tries to use
[Google Closure compiler](https://developers.google.com/closure/compiler/) that is expected to be in a file named
`compiler.jar`.
For CSS compression Yii assumes that [YUI Compressor](https://github.com/yui/yuicompressor/) is looked up in a file
named `yuicompressor.jar`.
In order to compress resources with these two you need to download both and place where your `yii` console bootstrap
file is using named mentioned above. Since both are Java tools you need JRE installed.
### Performing compression
After configuration is adjusted you can run the `compress` action, using created config:
