JS实现一次性弹窗的方法【刷新后不弹出】

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script>
  function openwin() {
    window.open("","","width=200,height=200");
  }
  function get_cookie(name) {
    var search = name+"=";
    var returnvalue = "";
    if(document.cookie.length>0) {
      offset = document.cookie.indexOf(search);
      if(offset!=-1) {
        offset = search.length;
        end = document.cookie.indexOf(";",offset);
        if(end==-1) {
          end = document.cookie.length;
        }
        returnvalue = unescape(document.cookie.substring(offset,end));
      }
    }
    return returnvalue;
  }
  function loadpopup() {
    if(get_cookie("popped")=='') {
      openwin();
      document.cookie="popped=yes";
    }
  }
</script>
</head>
<body onload="loadpopup();">
</body>
</html>