How to Minify JavaScripts and Stylesheets with YUI Compressor

How to Minify JavaScripts and Stylesheets with YUI Compressor


The YUI Compressor is no longer maintained by Yahoo. That's why you are strongly advised to avoid using YUI utilities unless strictly necessary. Read How to Minify CSS/JS Files (Using UglifyJS and UglifyCSS) for a modern and up-to-date alternative.

Yahoo! provides an excellent utility for minifying JavaScripts and stylesheets so they travel over the wire faster, the YUI Compressor. Thanks to Assetic, you can take advantage of this tool very easily.

Download the YUI Compressor JAR

The YUI Compressor is written in Java and distributed as a JAR. Download the JAR from the Yahoo! website and save it to app/Resources/java/yuicompressor.jar.

Configure the YUI Filters

Now you need to configure two Assetic filters in your application, one for minifying JavaScripts with the YUI Compressor and one for minifying stylesheets:


Windows users need to remember to update config to proper Java location. In Windows7 x64 bit by default it's C:\Program Files (x86)\Java\jre6\bin\java.exe.

You now have access to two new Assetic filters in your application: yui_css and yui_js. These will use the YUI Compressor to minify stylesheets and JavaScripts, respectively.

Minify your Assets

You have YUI Compressor configured now, but nothing is going to happen until you apply one of these filters to an asset. Since your assets are a part of the view layer, this work is done in your templates:


The above example assumes that you have a bundle called AppBundle and your JavaScript files are in the Resources/public/js directory under your bundle. This isn't important however - you can include your JavaScript files no matter where they are.

With the addition of the yui_js filter to the asset tags above, you should now see minified JavaScripts coming over the wire much faster. The same process can be repeated to minify your stylesheets.

Disable Minification in Debug Mode

Minified JavaScripts and stylesheets are very difficult to read, let alone debug. Because of this, Assetic lets you disable a certain filter when your application is in debug mode. You can do this by prefixing the filter name in your template with a question mark: ?. This tells Assetic to only apply this filter when debug mode is off.


Instead of adding the filter to the asset tags, you can also globally enable it by adding the apply_to attribute to the filter configuration, for example in the yui_js filter apply_to: "\.js$". To only have the filter applied in production, add this to the config_prod file rather than the common config file. For details on applying filters by file extension, see Filtering Based on a File Extension.

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