jquery, domain, get URL

You don't need jQuery for this, as simple javascript will suffice:

alert(document.domain);

See it in action:

console.log("Output;");  
console.log(location.hostname);
console.log(document.domain);
alert(window.location.hostname)

console.log("document.URL : "+document.URL);
console.log("document.location.href : "+document.location.href);
console.log("document.location.origin : "+document.location.origin);
console.log("document.location.hostname : "+document.location.hostname);
console.log("document.location.host : "+document.location.host);
console.log("document.location.pathname : "+document.location.pathname);

For further domain-related values, check out the properties of window.location online. You may find that location.host is a better option, as its content could differ from document.domain. For instance, the url http://192.168.1.80:8080 will have only the ipaddress in document.domain, but both the ipaddress and port number in location.host.

EDIT:

If you don't need to support IE10, you can simply use: document.location.origin

Original answer, if you need legacy support

You can get all this and more by inspecting the location object:

location = {
  host: "stackoverflow.com",
  hostname: "stackoverflow.com",
  href: "http://stackoverflow.com/questions/2300771/jquery-domain-get-url",
  pathname: "/questions/2300771/jquery-domain-get-url",
  port: "",
  protocol: "http:"
}

so:

location.host 

would be the domain, in this case stackoverflow.com. For the complete first part of the url, you can use:

location.protocol + "//" + location.host

which in this case would be http://stackoverflow.com

No jQuery required.

Similar to the answer before there there is

location.host

The location global has more fun facts about the current url as well. ( protocol, host, port, pathname, search, hash )