How to set Tridion ApplicationData using Anguilla JavaScript?

I have a Tab GUI Extension with a form and a text field. I would like to save the values of the form field to ApplicatioData. I was thinking of an 'Update' button calling an Anguilla method.

Is there an Anguilla method to do this? I don't see any method in Anguilla for this. Start of the code:

var c = $display.getItem();
var uri = c.getId();

Anguilla doesn't expose any (webservice or JavaScript) methods to generically modify ApplicationData. You will have to provide your own server-side code to set the ApplicationData.

So in my last need for this I wrote a simply WCF web service that sets the application data:

[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Multiple)]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]
[ServiceContract(Namespace= "ExtensionsModel.Services")]
public class ExtensionsService
{
    [OperationContract]
    [WebInvoke(Method = "POST",
                RequestFormat = WebMessageFormat.Json,
                ResponseFormat = WebMessageFormat.Json)]
    public void SetEnabled(string[] itemIDs, bool enabled)
    {
        using (var client = TridionCoreService.GetSessionAwareClient())
        {
            var appdata = new ApplicationData();
            appdata.ApplicationId = "ext:IsEnabled";
            appdata.Data = new ASCIIEncoding().GetBytes(enabled ? bool.TrueString : bool.FalseString);
            foreach (var itemID in itemIDs)
            {
                client.SaveApplicationData(itemID, new[] {appdata});
            }
        }
    }
}

Wired it up in the configuration file of my model:

<?xml version="1.0" encoding="utf-8" ?>
<Configuration> <!-- namespaces removed for readability -->
  <resources cache="true">
    <cfg:filters/>
    <cfg:groups>
      <cfg:group name="Extensions.Models">
        <cfg:domainmodel name="Extensions.Models">
          <cfg:services>
            <cfg:service type="wcf">Services/ExtensionsService.svc</cfg:service>
          </cfg:services>
        </cfg:domainmodel>
      </cfg:group>
    </cfg:groups>
  ...

And then call this web method from my command._execute

Extensions.Commands.DisableExtension.prototype._execute = function (selection) {
  ExtensionsModel.Services.ExtensionsService.SetEnabled(selection.getItems(), false);
};