How to open as popUp instead of New Tab

This question is frequently asking, I am looking for answer too. However I could't find, I have tried lots of example. While trying, I closed pop-up blockers and other restriction.

If new age browsers, automatically block pop-ups, according to me it is unlogical to use 'window.open()'.

However I would like to share with you my example onJsFiddle, maybe one of you lead me to solve.

//html
    <button onclick="showAsReservation('http://www.ucaknezaman.com'); retu false;">
    Test Link
    </button>

//javascript

var windowObjectReference = null; // global variable

function showAsReservation(url){    
   if(windowObjectReference == null || windowObjectReference.closed){
        windowObjectReference = window.open(url,
            "_blank","toolbar=no,scrollbars=no, resizable=yes,top=500, left=500, width=400, height=400");
      }
      else
      {
        windowObjectReference.focus();
      };
    windowObjectReference.focus();
}