Version 4 supported
This version of Silverstripe CMS is still supported though will not receive any additional features. Go to documentation for the most recent stable version.


The requirements class takes care of including CSS and JavaScript into your applications. This is preferred to hard coding any references in the <head> tag of your template, as it enables a more flexible handling through the Requirements class.

The examples below are using certain folder naming conventions (CSS files in css/, JavaScript files in javascript/). Silverstripe CMS core modules like cms use a different naming convention (CSS and JavaScript files in client/src/). The Requirements class can work with arbitrary file paths.

Exposing static assets

Before requiring static asset files in PHP code or in a template, those assets need to be "exposed". This process allows Silverstripe CMS projects and Silverstripe CMS modules to make static asset files available via the web server from locations that would otherwise be blocked from web server access, such as the vendor folder.

Configuring your project "exposed" folders

Exposed assets are made available in your web root in a dedicated "resources" directory. Prior to Silverstripe CMS 4.4, the name of this directory was hardcoded to resources. In Silverstripe CMS 4.4 and above, the name of the resources directory can be configured by defining the extra.resources-dir key in your composer.json. Silverstripe CMS projects created from silverstripe/installer 4.4 and above will automatically be configured to use _resources as their resource directory.

Each folder that needs to be exposed must be entered under the extra.expose key in your composer.json file. Module developers should use a path relative to the root of their module (don't include the "vendor/package-developer/package-name" path).

This is a sample Silverstripe CMS project composer.json file configured to expose some assets.

    "name": "app/myproject",
    "type": "silverstripe-project",
    "require": {
        "silverstripe/recipe-cms": "4.4.x-dev"
    "extra": {
        "resources-dir": "_resources",
        "expose": [

Files contained inside the app/client/dist and app/images will be made publicly available under the _resources directory.

Silverstripe CMS projects should not track the "resources" directory in their source control system.

Exposing assets in the web root

Silverstripe CMS projects ship with silverstripe/vendor-plugin. This Composer plugin automatically tries to expose assets from your project and installed modules after installation, or after an update.

Developers can explicitly expose static assets by calling composer vendor-expose. This is necessary after updating your resources-dir or expose configuration in your composer.json file.

composer vendor-expose accepts an optional method argument (e.g: composer vendor-expose auto). This controls how the files are exposed in the "resources" directory:

  • none disables all symlink / copy
  • copy copies the exposed files
  • symlink create symbolic links to the exposed folder
  • junction uses a junction (Windows only)
  • auto creates symbolic links (or junctions on Windows), but fails over to copy.

Referencing exposed assets

When referencing exposed static assets, use either the project file path (relative to the project root folder) or a module name and relative file path to that module's root folder. e.g:

use SilverStripe\View\Requirements;

// When referencing project files, use the same path defined in your `composer.json` file.

// When referencing theme files, use a path relative to the root of your project

// When referencing files from a module, you need to prefix the path with the module name.

When rendered in HTML code, these URLs will be rewritten to their matching path inside the "resources" directory.

Template requirements API

<%-- <my-module-dir>/templates/ --%>
<% require css("<my-module-dir>/css/some_file.css") %>
<% require themedCSS("some_themed_file") %>
<% require javascript("<my-module-dir>/javascript/some_file.js") %>

Requiring assets from the template is restricted compared to the PHP API.

PHP requirements API

It is common practice to include most Requirements either in the init()-method of your controller, or as close to rendering as possible (e.g. in FormField).

namespace App\Control;

use SilverStripe\View\Requirements;

class MyCustomController extends Controller
    protected function init()


CSS files

use SilverStripe\View\Requirements;

Requirements::css($path, $media);

If you're using the CSS method a second argument can be used. This argument defines the 'media' attribute of the <link> element, so you can define 'screen' or 'print' for example.

Requirements::css('<my-module-dir>/css/some_file.css', 'screen,projection');

JavaScript files

use SilverStripe\View\Requirements;

Requirements::javascript($path, $options);

A variant on the inclusion of custom JavaScript is the inclusion of templated JavaScript. Here, you keep your JavaScript in a separate file and instead load, via search and replace, several PHP generated variables into that code.

use SilverStripe\Security\Security;
use SilverStripe\View\Requirements;

$vars = [
    'MemberID' => Security::getCurrentUser()->ID,

Requirements::javascriptTemplate('<my-module-dir>/javascript/some_file.js', $vars);

In this example, some_file.js is expected to contain a replaceable variable expressed as MemberID.

If you are using front-end script combination mechanisms, you can optionally declare that your included files provide these scripts. This will ensure that subsequent Requirement calls that rely on those included scripts will not double include those files.

use SilverStripe\View\Requirements;

Requirements::javascript('<my-module-dir>/javascript/dist/bundle.js', ['provides' => [
// Will skip this file

You can also use the second argument to add the 'async' and/or 'defer attributes to the script tag generated:

use SilverStripe\View\Requirements;

        'async' => true,
        'defer' => true,

Custom inline CSS or JavaScript

You can also quote custom scripts directly. This may seem a bit ugly, but is useful when you need to transfer some kind of 'configuration' from the database in a raw format. You'll need to use the heredoc syntax to quote JS and CSS, this is generally speaking the best way to do these things - it clearly marks the copy as belonging to a different language.

use SilverStripe\View\Requirements;

  alert("hi there");

  .tree li.$className {
    background-image: url($icon);

Combining files

You can concatenate several CSS or JavaScript files into a single dynamically generated file. This increases performance by reducing HTTP requests.

use SilverStripe\View\Requirements;


To make debugging easier in your local environment, combined files is disabled when running your application in dev mode. You can re-enable dev combination by setting Requirements_Backend.combine_in_dev to true.

Configuring combined file storage

In some situations or server configurations, it may be necessary to customise the behaviour of generated JavaScript files in order to ensure that current files are served in requests.

By default, files will be generated on demand in the format assets/_combinedfiles/name-<hash>.js, where <hash> represents the hash of the source files used to generate that content. The default flysystem backend, as used by the [AssetStore](api:SilverStripe\Assets\Storage\AssetStore) backend, is used for this storage, but it can be substituted for any other backend.

You can also use any of the below options in order to tweak this behaviour:

  • Requirements.disable_flush_combined - By default all combined files are deleted on flush. If combined files are stored in source control, and thus updated manually, you might want to turn this on to disable this behaviour.
  • Requirements_Backend.combine_hash_querystring - By default the <hash> of the source files is appended to the end of the combined file (prior to the file extension). If combined files are versioned in source control, or running in a distributed environment (such as one where the newest version of a file may not always be immediately available) then it may sometimes be necessary to disable this. When this is set to true, the hash will instead be appended via a querystring parameter to enable cache busting, but not in the filename itself. I.e. assets/_combinedfiles/name.js?m=<hash>
  • Requirements_Backend.default_combined_files_folder - This defaults to _combinedfiles, and is the folder within the configured asset backend that combined files will be stored in. If using a backend shared with other systems, it is usually necessary to distinguish combined files from other assets.
  • Requirements_Backend.combine_in_dev - By default combined files will not be combined except in test or live environments. Turning this on will allow for pre-combining of files in development mode.
  • Requirements_Backend.resolve_relative_css_refs - Enables rewriting of relative paths to image/font assets to accommodate the fact that the combined CSS is placed in a totally different folder than the source CSS files. Disabled by default.

In some cases it may be necessary to create a new storage backend for combined files, if the default location is not appropriate. Normally a single backend is used for all site assets, so a number of objects must be replaced. For instance, the below will set a new set of dependencies to write to app/javascript/combined

Name: myrequirements
  disable_flush_combined: true
  combine_in_dev: true
  combine_hash_querystring: true
  default_combined_files_folder: 'combined'
  resolve_relative_css_refs: true
  # Create adapter that points to the custom directory root
    class: SilverStripe\Assets\Flysystem\PublicAssetAdapter
      Root: ./app/javascript
  # Set flysystem filesystem that uses this adapter
    class: 'League\Flysystem\Filesystem'
      Adapter: '%$SilverStripe\Assets\Flysystem\PublicAdapter.custom-adapter'
  # Create handler to generate assets using this filesystem
    class: SilverStripe\Assets\Flysystem\GeneratedAssets
      Filesystem: '%$League\Flysystem\Filesystem.custom-filesystem'
  # Assign this generator to the requirements builder
      AssetHandler: '%$SilverStripe\Assets\Storage\GeneratedAssetHandler.custom-generated-assets'

In the above configuration, automatic expiry of generated files has been disabled, and it is necessary for the developer to maintain these files manually. This may be useful in environments where assets must be pre-cached, where scripts must be served alongside static files, or where no framework PHP request is guaranteed. Alternatively, files may be served from instances other than the one which generated the page response, and file synchronisation might not occur fast enough to propagate combined files to mirrored filesystems.

In any case, care should be taken to determine the mechanism appropriate for your development and production environments.

Combined CSS files

You can also combine CSS files into a media-specific stylesheets as you would with the Requirements::css call - use the third parameter of the combine_files function:

use SilverStripe\View\Requirements;
use SilverStripe\View\SSViewer;
use SilverStripe\View\ThemeResourceLoader;

$loader = ThemeResourceLoader::inst();
$themes = SSViewer::get_themes();

$printStylesheets = [
    $loader->findThemedCSS('print_HomePage.css', $themes),
    $loader->findThemedCSS('print_Page.css', $themes),

Requirements::combine_files('print.css', $printStylesheets, 'print');

By default, all requirements files are flushed (deleted) when ?flush querystring parameter is set. This can be disabled by setting the Requirements.disable_flush_combined config to true.

When combining CSS files, take care of relative urls, as these will not be re-written to match the destination location of the resulting combined CSS.

Combined JS files

You can also add the 'async' and/or 'defer' attributes to combined JavaScript files as you would with the Requirements::javascript call - use the third parameter of the combine_files function:

use SilverStripe\View\Requirements;
use SilverStripe\View\SSViewer;
use SilverStripe\View\ThemeResourceLoader;

$loader = ThemeResourceLoader::inst();
$themes = SSViewer::get_themes();

$scripts = [
    $loader->findThemedJavascript('some_script.js', $themes),
    $loader->findThemedJavascript('some_other_script.js', $themes),

Requirements::combine_files('scripts.js', $scripts, ['async' => true, 'defer' => true]);

Minification of CSS and JS files

You can minify combined JavaScript and CSS files at runtime using an implementation of the SilverStripe\View\Requirements_Minifier interface.

namespace App;

use SilverStripe\View\Requirements_Minifier;

class MyMinifier implements Requirements_Minifier
     * Minify the given content
     * @param string $content
     * @param string $type Either js or css
     * @param string $filename Name of file to display in case of error
     * @return string minified content
    public function minify($content, $type, $fileName)
        // Minify $content;

        return $minifiedContent;

Then, inject this service in Requirements_Backend.

      MinifyCombinedFiles: true
      Minifier: '%$App\MyMinifier'

While the framework does afford you the option of minification at runtime, we recommend using one of many frontend build tools to do this for you, e.g. Webpack, Gulp, or Grunt.

Clearing assets

use SilverStripe\View\Requirements;


Clears all defined requirements. You can also clear specific requirements.

use SilverStripe\View\Requirements;


Depending on where you call this command, a Requirement might be re-included afterwards.


Requirements can also be explicitly blocked from inclusion, which is useful to avoid conflicting JavaScript logic or CSS rules. These blocking rules are independent of where the block() call is made. It applies both for already included requirements, and ones included after the block() call.

One common example is to block the core jquery.js added by various form fields and core controllers, and use a newer version in a custom location. This assumes you have tested your application with the newer version.

use SilverStripe\View\Requirements;


The CMS also uses the Requirements system, and its operation can be affected by block() calls. Avoid this by limiting the scope of your blocking operations, e.g. in init() of your controller.

Inclusion order

Requirements acts like a stack, where everything is rendered sequentially in the order it was included. There is no way to change inclusion-order, other than using Requirements::clear and rebuilding the whole set of requirements.

Inclusion order is both relevant for CSS and JavaScript files in terms of dependencies, inheritance and overlays - be careful when messing with the order of requirements.

JavaScript placement

By default, Silverstripe CMS includes all JavaScript files at the bottom of the page body, unless there's another script already loaded, then, it's inserted before the first <script> tag. If this causes problems, it can be configured.

use SilverStripe\View\Requirements;


Requirements.force_js_to_bottom, will force Silverstripe CMS to write the JavaScript to the bottom of the page body, even if there is an earlier script tag.

If the JavaScript files are preferred to be placed in the <head> tag rather than in the <body> tag, Requirements.write_js_to_body should be set to false.

use SilverStripe\View\Requirements;


Direct resource urls

In templates, you can use the $resourcePath() or $resourceURL() helper methods to inject links to resources directly. If you want to link to resources within a specific module you can use the vendor/module:some/path/to/file.jpg syntax.

For example:

<div class="loading">
    <img src="$resourceURL('silverstripe/admin:client/dist/images/spinner.gif')" />

In PHP you can directly resolve these urls using the ModuleResourceLoader helper.

use SilverStripe\Core\Manifest\ModuleResourceLoader;

$file = ModuleResourceLoader::singleton()

Related lessons

API documentation