完整实例 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>蜜蜂教程(mifengjc.com)</title>
</head>
<head>
  <script>
    function setCookie(cname, cvalue, exdays) {
      var d = new Date();
      d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
      var expires = "expires=" + d.toGMTString();
      document.cookie = cname + "=" + cvalue + "; " + expires;
    }

    function getCookie(cname) {
      var name = cname + "=";
      var ca = document.cookie.split(';');
      for (var i = 0; i < ca.length; i++) {
        var c = ca[i].trim();
        if (c.indexOf(name) == 0) return c.substring(name.length, c.length);
      }
      return "";
    }

    function checkCookie() {
      var user = getCookie("username");
      if (user != "") {
        alert("Welcome again " + user);
      } else {
        user = prompt("Please enter your name:", "");
        if (user != "" & user != null) {
          setCookie("username", user, 30);
        }
      }
    }
  </script>
</head>

<body onload="checkCookie()"></body>

</html>
        