System.Diagnostics.Trace.Write()

Microsoft.LightSwitch.Trace.TraceInformation("test info");
Microsoft.LightSwitch.Trace.TraceError(new Exception("test exception"));

Microsoft.LightSwitch.Trace.TraceInformation("CustomCategory", "test info");

<!-- The semicolon-separated list of categories that will be enabled at the specified trace level -->
<add key="Microsoft.LightSwitch.Trace.Categories" value="Microsoft.LightSwitch;CustomCategory" />

var message = encodeURIComponent("Hello JavaScript World");
var url = "../api/Trace/Information/" + message;
$.ajax({
    type: "GET",
    url: url,
    context: document.body
});

Microsoft.LightSwitch.Threading.Dispatchers.Main.BeginInvoke(async () =>
    {
        System.Net.WebRequest.RegisterPrefix("http://", System.Net.Browser.WebRequestCreator.BrowserHttp);
        System.Net.WebRequest.RegisterPrefix("https://", System.Net.Browser.WebRequestCreator.BrowserHttp);
        var message = "Hello Silverlight World";
        var uri = new Uri(System.Windows.Application.Current.Host.Source, "/api/Trace/Information/" + message);
        var request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(uri);
        request.BeginGetResponse(ac => { }, null);
    });
}