retrieve local proxy setting via getProxyConfigurationAsync

Question

I'm using javascript to developing Windows Store app. I'm having trouble in using getProxyConfigurationAsync() to retrieve local http/https proxy settings. My codes are sth. like these:

var uri = new Windows.Foundation.Uri("http://localhost");

Windows.Networking.Connectivity.NetworkInformation.getProxyConfigurationAsync(uri).done(myOnDone, myOnError, myOnProgress);

But none of the 3 callbacks got called. I also tried 127.0.0.1 with no luck.

I'm not sure if I'm doing this right, especially about uri part. Is there any sample code to show the usage of getProxyConfigurationAsync()? And even myOnDone callback got called, I've no idea about where I could get proxy info.

Any advice? Thanks!