How to Use Assetic for Asset Management

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Read the updated version of this page for Symfony 7.1 (the current stable version).

Installing and Enabling Assetic

Starting from Symfony 2.8, Assetic is no longer included by default in the Symfony Standard Edition. Before using any of its features, install the AsseticBundle executing this console command in your project:

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$ composer require symfony/assetic-bundle

Then, enable the bundle in the AppKernel.php file of your Symfony application:

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// app/AppKernel.php

// ...
class AppKernel extends Kernel
{
    // ...

    public function registerBundles()
    {
        $bundles = array(
            // ...
            new Symfony\Bundle\AsseticBundle\AsseticBundle(),
        );

        // ...
    }
}

Finally, add the following minimal configuration to enable Assetic support in your application:

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# app/config/config.yml
assetic:
    debug:          '%kernel.debug%'
    use_controller: '%kernel.debug%'
    filters:
        cssrewrite: ~

# ...

Introducing Assetic

Assetic combines two major ideas: assets and filters. The assets are files such as CSS, JavaScript and image files. The filters are things that can be applied to these files before they are served to the browser. This allows a separation between the asset files stored in the application and the files actually presented to the user.

Without Assetic, you just serve the files that are stored in the application directly:

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<script src="{{ asset('js/script.js') }}"></script>

But with Assetic, you can manipulate these assets however you want (or load them from anywhere) before serving them. This means you can:

  • Minify and combine all of your CSS and JS files
  • Run all (or just some) of your CSS or JS files through some sort of compiler, such as LESS, SASS or CoffeeScript
  • Run image optimizations on your images

Assets

Using Assetic provides many advantages over directly serving the files. The files do not need to be stored where they are served from and can be drawn from various sources such as from within a bundle.

You can use Assetic to process CSS stylesheets, JavaScript files and images. The philosophy behind adding either is basically the same, but with a slightly different syntax.

Including JavaScript Files

To include JavaScript files, use the javascripts tag in any template:

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{% javascripts '@AppBundle/Resources/public/js/*' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

Note

If your application templates use the default block names from the Symfony Standard Edition, the javascripts tag will most commonly live in the javascripts block:

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{# ... #}
{% block javascripts %}
    {% javascripts '@AppBundle/Resources/public/js/*' %}
        <script src="{{ asset_url }}"></script>
    {% endjavascripts %}
{% endblock %}
{# ... #}

Tip

You can also include CSS stylesheets: see How to Use Assetic for Asset Management.

In this example, all files in the Resources/public/js/ directory of the AppBundle will be loaded and served from a different location. The actual rendered tag might simply look like:

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<script src="/app_dev.php/js/abcd123.js"></script>

This is a key point: once you let Assetic handle your assets, the files are served from a different location. This will cause problems with CSS files that reference images by their relative path. See How to Use Assetic for Asset Management.

Including CSS Stylesheets

To bring in CSS stylesheets, you can use the same technique explained above, except with the stylesheets tag:

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{% stylesheets 'bundles/app/css/*' filter='cssrewrite' %}
    <link rel="stylesheet" href="{{ asset_url }}" />
{% endstylesheets %}

Note

If your application templates use the default block names from the Symfony Standard Edition, the stylesheets tag will most commonly live in the stylesheets block:

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{# ... #}
{% block stylesheets %}
    {% stylesheets 'bundles/app/css/*' filter='cssrewrite' %}
        <link rel="stylesheet" href="{{ asset_url }}" />
    {% endstylesheets %}
{% endblock %}
{# ... #}

But because Assetic changes the paths to your assets, this will break any background images (or other paths) that uses relative paths, unless you use the cssrewrite filter.

Note

Notice that in the original example that included JavaScript files, you referred to the files using a path like @AppBundle/Resources/public/file.js, but that in this example, you referred to the CSS files using their actual, publicly-accessible path: bundles/app/css. You can use either, except that there is a known issue that causes the cssrewrite filter to fail when using the @AppBundle syntax for CSS stylesheets.

Including Images

To include an image you can use the image tag.

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{% image '@AppBundle/Resources/public/images/example.jpg' %}
    <img src="{{ asset_url }}" alt="Example" />
{% endimage %}

You can also use Assetic for image optimization. More information in How to Use Assetic for Image Optimization with Twig Functions.

Tip

Instead of using Assetic to include images, you may consider using the LiipImagineBundle community bundle, which allows to compress and manipulate images (rotate, resize, watermark, etc.) before serving them.

Fixing CSS Paths with the cssrewrite Filter

Since Assetic generates new URLs for your assets, any relative paths inside your CSS files will break. To fix this, make sure to use the cssrewrite filter with your stylesheets tag. This parses your CSS files and corrects the paths internally to reflect the new location.

You can see an example in the previous section.

Caution

When using the cssrewrite filter, don't refer to your CSS files using the @AppBundle syntax. See the note in the above section for details.

Combining Assets

One feature of Assetic is that it will combine many files into one. This helps to reduce the number of HTTP requests, which is great for front-end performance. It also allows you to maintain the files more easily by splitting them into manageable parts. This can help with re-usability as you can easily split project-specific files from those which can be used in other applications, but still serve them as a single file:

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{% javascripts
    '@AppBundle/Resources/public/js/*'
    '@AcmeBarBundle/Resources/public/js/form.js'
    '@AcmeBarBundle/Resources/public/js/calendar.js' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

In the dev environment, each file is still served individually, so that you can debug problems more easily. However, in the prod environment (or more specifically, when the debug flag is false), this will be rendered as a single script tag, which contains the contents of all of the JavaScript files.

Tip

If you're new to Assetic and try to use your application in the prod environment (by using the app.php controller), you'll likely see that all of your CSS and JS breaks. Don't worry! This is on purpose. For details on using Assetic in the prod environment, see How to Use Assetic for Asset Management.

And combining files doesn't only apply to your files. You can also use Assetic to combine third party assets, such as jQuery, with your own into a single file:

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{% javascripts
    '@AppBundle/Resources/public/js/thirdparty/jquery.js'
    '@AppBundle/Resources/public/js/*' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

Using Named Assets

AsseticBundle configuration directives allow you to define named asset sets. You can do so by defining the input files, filters and output files in your configuration under the assetic section. Read more in the assetic config reference.

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# app/config/config.yml
assetic:
    assets:
        jquery_and_ui:
            inputs:
                - '@AppBundle/Resources/public/js/thirdparty/jquery.js'
                - '@AppBundle/Resources/public/js/thirdparty/jquery.ui.js'

After you have defined the named assets, you can reference them in your templates with the @named_asset notation:

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{% javascripts
    '@jquery_and_ui'
    '@AppBundle/Resources/public/js/*' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

Filters

Once they're managed by Assetic, you can apply filters to your assets before they are served. This includes filters that compress the output of your assets for smaller file sizes (and better frontend optimization). Other filters can compile CoffeeScript files to JavaScript and process SASS into CSS. In fact, Assetic has a long list of available filters.

Many of the filters do not do the work directly, but use existing third-party libraries to do the heavy-lifting. This means that you'll often need to install a third-party library to use a filter. The great advantage of using Assetic to invoke these libraries (as opposed to using them directly) is that instead of having to run them manually after you work on the files, Assetic will take care of this for you and remove this step altogether from your development and deployment processes.

To use a filter, you first need to specify it in the Assetic configuration. Adding a filter here doesn't mean it's being used - it just means that it's available to use (you'll use the filter below).

For example to use the UglifyJS JavaScript minifier the following configuration should be defined:

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# app/config/config.yml
assetic:
    filters:
        uglifyjs2:
            bin: /usr/local/bin/uglifyjs

Now, to actually use the filter on a group of JavaScript files, add it into your template:

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{% javascripts '@AppBundle/Resources/public/js/*' filter='uglifyjs2' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

A more detailed guide about configuring and using Assetic filters as well as details of Assetic's debug mode can be found in How to Minify CSS/JS Files (Using UglifyJS and UglifyCSS).

Controlling the URL Used

If you wish to, you can control the URLs that Assetic produces. This is done from the template and is relative to the public document root:

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{% javascripts '@AppBundle/Resources/public/js/*' output='js/compiled/main.js' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}

Note

Symfony also contains a method for cache busting, where the final URL generated by Assetic contains a query parameter that can be incremented via configuration on each deployment. For more information, see the Framework Configuration Reference (FrameworkBundle) configuration option.

Dumping Asset Files

In the dev environment, Assetic generates paths to CSS and JavaScript files that don't physically exist on your computer. But they render nonetheless because an internal Symfony controller opens the files and serves back the content (after running any filters).

This kind of dynamic serving of processed assets is great because it means that you can immediately see the new state of any asset files you change. It's also bad, because it can be quite slow. If you're using a lot of filters, it might be downright frustrating.

Fortunately, Assetic provides a way to dump your assets to real files, instead of being generated dynamically.

Dumping Asset Files in the prod Environment

In the prod environment, your JS and CSS files are represented by a single tag each. In other words, instead of seeing each JavaScript file you're including in your source, you'll likely just see something like this:

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<script src="/js/abcd123.js"></script>

Moreover, that file does not actually exist, nor is it dynamically rendered by Symfony (as the asset files are in the dev environment). This is on purpose - letting Symfony generate these files dynamically in a production environment is just too slow.

Instead, each time you use your application in the prod environment (and therefore, each time you deploy), you should run the following command:

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$ php app/console assetic:dump --env=prod --no-debug

This will physically generate and write each file that you need (e.g. /js/abcd123.js). If you update any of your assets, you'll need to run this again to regenerate the file.

Dumping Asset Files in the dev Environment

By default, each asset path generated in the dev environment is handled dynamically by Symfony. This has no disadvantage (you can see your changes immediately), except that assets can load noticeably slow. If you feel like your assets are loading too slowly, follow this guide.

First, tell Symfony to stop trying to process these files dynamically. Make the following change in your config_dev.yml file:

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# app/config/config_dev.yml
assetic:
    use_controller: false

Next, since Symfony is no longer generating these assets for you, you'll need to dump them manually. To do so, run the following command:

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$ php app/console assetic:dump

This physically writes all of the asset files you need for your dev environment. The big disadvantage is that you need to run this each time you update an asset. Fortunately, by using the assetic:watch command, assets will be regenerated automatically as they change:

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$ php app/console assetic:watch

The assetic:watch command was introduced in AsseticBundle 2.4. In prior versions, you had to use the --watch option of the assetic:dump command for the same behavior.

Since running this command in the dev environment may generate a bunch of files, it's usually a good idea to point your generated asset files to some isolated directory (e.g. /js/compiled), to keep things organized:

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{% javascripts '@AppBundle/Resources/public/js/*' output='js/compiled/main.js' %}
    <script src="{{ asset_url }}"></script>
{% endjavascripts %}
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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