hostReachable.js

function hostReachable() {

  // Handle IE and more capable browsers
  var xhr = new ( window.ActiveXObject || XMLHttpRequest )( "Microsoft.XMLHTTP" );
  var status;
  var server = window.location.hostname;
  if (window.location.port != '') {
    server += ':'+window.location.port;
  }

  // Open new request as a HEAD to the root hostname with a random param to bust the cache
  xhr.open( "HEAD", "//" + server + "/?rand=" + Math.floor((1 + Math.random()) * 0x10000), false );

  // Issue request and handle response
  try {
    xhr.send();
    return ( xhr.status >= 200 && xhr.status < 300 || xhr.status === 304 );
  } catch (error) {
    return false;
  }

}

Because I m not good at javascript, I'd like to ask you why you prefer :

 if (window.location.port != '') {
  server += ':'+window.location.port;
}

instead of:

window.location.host

is there any fail with window.location.host ?

@Hettomei The XHR request needs to be sent to the server. If the server is listening on port 8080 for example, a request to a hostname without port 8080 will not give you a response.

it's Great, Thanks