The tilde is that symbol you get when you press the upper left most key while holding Shift and (when it is not denoting a finalizer) it denotes the root of a web application!

Observe:

Whatever whatever;
using (var reader = new StreamReader(HttpContext.Server.MapPath("~/SiteMap.xml")))
{
   var xmlSerializer = new XmlSerializer(typeof(Whatever));
   whatever = xmlSerializer.Deserialize(reader) as Whatever;
}

 
 

Do note that the code above is C# and not JavaScript and there is no tilde in JavaScript. In JavaScript you need to do something like this:

function whereAmI() {
   var url = window.location.href;
   var urlChunks = url.split("/");
   var url = "";
   var matchMade = false;
   urlChunks.forEach(function(chunk) {
      if(!matchMade){
         if (url == "http://" || url == "https://" || url == "http://localhost/" || url ==
               "https://localhost/") {
            if (chunk.toLowerCase() != "localhost") {
               matchMade = true;
            }
         }
         url = url + chunk.toLowerCase() + "/";
      }
   });
   if (url.indexOf("?") > -1) {
      urlChunks = url.split("?");
      url = urlChunks[0] + "/";
   };
   if (url.indexOf("&") > -1) {
      urlChunks = url.split("?");
      url = urlChunks[0] + "/";
   };
   return url;
};

 
 

Why didn't I just use window.location.hostname you ask? Because .hostname will not find the base url for an IIS application which will have a base like so: http://localhost/whatever/