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Javascript and CSS Resources

DotVVM has a built-in mechanism for managing resources. It supports JavaScript files, inline JavaScript snippets and CSS files. It is extensible so it can be used to work with fonts, icons and other kinds of static files.

The resources are named and stored in a global repository which is configured in DotVVM configuration.

Each resource can also specify its dependencies. Thanks to this, DotVVM can include all required resources in the page in the correct order.

And finally, if any DotVVM control needs a particular resource, it can request the resource to be included in the page. DotVVM keeps track of the resources needed by controls in the page and renders only the those which are really needed.

We have the following types of resources:

  • ScriptResource renders the <script> element and is used to include JavaScript files.

  • StylesheetResource renders the <link rel="stylesheet"> element and is used to include CSS files.

  • InlineScriptResource renders the <script> element with JavaScript code snippet.

  • NullResource is a special type of resource that doesn't render anything. It is used when some control requests the resource to be included in the page, however you have included the resource itself (e.g. in the master page).

Resource Repository

The resource registration has changed in DotVVM 1.1. Visit the Upgrading to DotVVM 1.1 for more details.

All resources are registered in resource repository found in the config.Resources collection.

You can register a new resource with the Register method. This method can also replace existing resources if they exists. The resources should be registered in the DotvvmStartup.cs file.

config.Resources.Register("bootstrap-css", new StylesheetResource()
{
    Location = new UrlResourceLocation("~/Content/bootstrap.min.css")
});
config.Resources.Register("bootstrap", new ScriptResource()
{
    Location = new UrlResourceLocation("~/Scripts/bootstrap.min.js"),
    Dependencies = new[] { "bootstrap-css", "jquery" }
});

In the code, you can retrieve the resource by its name using FindResource method. If you need to change the path for the jquery resource, you can do it like this:

var jquery = config.Resources.FindResource("jquery") as ScriptResource;
jquery.Location = new UrlResourceLocation("~/Scripts/jquery.2.1.1.min.js");
jquery.LocationFallback = null;

Resource Location

Most resources have the Location property of type IResourceLocation which defines, how the resource file is obtained. You can use one of the following implementations:

  • UrlResourceLocation specifies just the URL where the resource can be found. You can use either absolute URL (e.g. to point to some CDN), a relative URL to your server, or even a data URI. DotVVM will render the <script> or <link> element with the exact URL you have specified.

  • LocalFileResourceLocation expects the app-relative filesystem path to the script or stylesheet file. This path should not start with / - it would point to the root of the filesystem. DotVVM will render the <script> or <link> element which points to a DotVVM resource handler (~/dotvvmResource/checksum/resourceName) that will serve the resource. This is useful for bundling or advanced scenarios.

  • EmbeddedResourceLocation can extract the embedded resource from an assembly. This is very useful if you need to pack some DotVVM controls in a library and embed the resources in the DLL file.

You can of course implement custom resource types and resource location implementations.

CDN Fallbacks

If you want to use CDN for script files, it is often a good idea to have a local fallback for the case that CDN is down, or if you are debugging the app without the Internet connection.

There is a property called LocationFallback. If it is set, the framework will try to load the script from the primary location (the CDN) first and will use the ResourceLocationFallback.JavasciptCondition to check whether the resource has loaded successfully. The JavascriptCondition property should contain a JavaScript expression which evaluates to true when used in the if statement. For jQuery, you can use window.jQuery.

If the resource could not be loaded from the CDN, it would fall back to the AlternativeLocations and use the first one that works.

configuration.Resources.Register(ResourceConstants.JQueryResourceName,
	new ScriptResource()
	{
		Location = new UrlResourceLocation("https://code.jquery.com/jquery-2.1.1.min.js"),
		LocationFallback = new ResourceLocationFallback("window.jQuery", new EmbeddedResourceLocation(typeof(DotvvmConfiguration).GetType().Assembly, "DotVVM.Framework.Resources.Scripts.jquery-2.1.1.min.js")),
		VerifyResourceIntegrity = true
	});

If the VerifyResourceIntegrity property on the ScriptResource is set to true, then it will use the LocationFallback to automatically compute the subresource integrity hash, for an extra guarantee that the remote resource being downloaded is the one intended.

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