JavaScript实现下班倒计时及桌面通知功能

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <meta name="author" content="By jxqlovejava" />
  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
  <title>下班倒计时</title>
  <style type="text/css">
    body {
      color:#333;
      font-family:meiryo, Arial, Helvetica, sans-serif;
      font-size:12px;
      height:100%;
      margin:0 auto;
      padding:0;
      width:100%;
    }
    html,body,div,dl,dt,dd,ul,ol,li,th,td {
      margin:0;
      padding:0;
    }
    body {
      background-color: #ccc;
    }
    #counterContainer {
      width:270px;
      height:150px;
      position:absolute;
      left:50%;
      top:50%;
      margin:-75px 0 0 -135px;
      border: 1px solid #ccc;
      background-color: #fff;
    }
    #timeContainer, #toolBarContainer, #msgContainer {
      text-align: center;
    }
    #timeContainer {
      margin-top: 38px;
    }
    #toolBarContainer {
      margin-top: 15px;
    }
    .timeBox {
      width: 30px;
    }
    #minute, #second {
      text-align: center;
    }
    .highLight {
      font-weight: bold;
      color: green;
    }
    .bt {
      width: 84px;
    }
    #msg {
      visibility:hidden;
      padding-top: 10px;
    }
  </style>
</head>
<body>
  <div id="counterContainer">
    <div id="timeContainer">
      还有
      <input type="text" id="minute" class="timeBox" value="00">分&nbsp;
      <input type="text" id="second" class="timeBox" value="00">秒&nbsp;
      <span class="highLight">下班！</span>
    </div>
    <div id="toolBarContainer">
      <input type="button" id="setOrResetBt" class="bt" value="设定" />
      <input type="button" id="startBt" class="bt" value="开始倒计时!" />
    </div>
    <div id="msgContainer">
      <span id="msg" class="highLight">可以下班了，哦耶~~</span>
    </div>
  </div>
  <script type="text/javascript" src="jquery-1.7.1.min.js"></script>
  <script type="text/javascript">
    var minuteLeft;   // 剩下的分
    var secondLeft;   // 剩下的秒
    var totalSeconds;  // 剩下的总秒数
    var myInterval;   // 倒计时用的time interval
    var isCounting = false; // 是否正在倒计时
    var hasSetted = false; // 是否已设定完毕
    var charLimit = 2; // 分和秒都只能为2位
    // 桌面通知
    function sendDesktopNotification(title, msg) {
      if(!window.webkitNotifications || (window.webkitNotifications.checkPermission()!=0)) { // 不支持桌面通知或未授权
        alert("不好意思，你的浏览器不支持桌面通知或者你未开启！");
        return; // 不支持桌面通知
      }
      var notificationMsgBox = window.webkitNotifications.createNotification(icon="images/favicon.ico", title, msg);
      notificationMsgBox.show();
    }
    $(function() {
      // 将两位字符串转成00-59格式
      function convertToStandardFormat(timeInput) {
        var val = $(timeInput).val();
        if(val.length == 0) {
          return;
        }
        else if(val.length == 1) {
          if(isNaN(val)) {
            $(timeInput).val('0');
          }
        }
        else if(val.length == 2 || val.length == 3) {
          var intVal = parseInt(val, 10);
          if(isNaN(intVal) || intVal <= 0) {
            $(timeInput).val('00');
          }
          else {
            var firstDigit = parseInt(val[0]);
            if(firstDigit > 5) {
              firstDigit = 0;
            }
            $(timeInput).val(firstDigit+val[1]);
          }
        }
      }
      // 限制分输入框和秒输入框都只能输入两个字符且范围为00-59
      $("#minute").keyup(function(e) {
        if(e.keyCode == 37 || e.keyCode == 39) // 方向键
          return;
        convertToStandardFormat($(this));
      });
      $("#second").keyup(function(e) {
        if(e.keyCode == 37 || e.keyCode == 39) // 方向键
          return;
        convertToStandardFormat($(this));
      });
      $("#setOrResetBt").click(function() {
        if($(this).val() === "设定") {
          if(parseInt($("#minute").val(), 10) == 0 && parseInt($("#second").val(), 10) == 0) {
            alert("请设定分、秒为0到59范围内的数字！");
            return;
          }
          hasSetted = true;
          // 设置分输入框和秒输入框不可编辑
          $("#minute").attr("readonly", true);
          $("#second").attr("readonly", true);
          minuteLeft = parseInt($("#minute").val(), 10);
          secondLeft = parseInt($("#second").val(), 10);
          totalSeconds = minuteLeft*60 + secondLeft;
          // 按钮文字切换
          $(this).val("重置");
        }
        else { // 点击了重置按钮
          clearInterval(myInterval);
          isCounting = false;
          hasSetted = false;
          $("#msg").css("visibility", "hidden");
          // 设置分输入框和秒输入框可编辑
          $("#minute").attr("readonly", false);
          $("#second").attr("readonly", false);
          $("#minute").val("00");
          $("#second").val("00");
          // 按钮文字切换
          $(this).val("设定");
        }
      }); 
      $("#startBt").click(function() {
        if(!hasSetted) {
          alert("请先设定时间！")
          return;
        }
        if(!isCounting) {
          myInterval = setInterval(function() {
            totalSeconds--;
            if(secondLeft == 0 && minuteLeft > 0) {
              minuteLeft--;
              secondLeft = 59;
            }
            else {
              secondLeft--;
            }
            // 更新分秒显示
            $("#minute").val(minuteLeft > 9 ? minuteLeft : ('0'+minuteLeft));
            $("#second").val(secondLeft > 9 ? secondLeft : ('0'+secondLeft));
            if(totalSeconds==0) {  // 下班时间到了
              clearInterval(myInterval);
              $("#msg").css("visibility", "visible");
              sendDesktopNotification("下班了", "亲，下班了！\nHappy Weekend!");
            }
          }, 1000); // 每一秒钟更新一下时间
        }
        isCounting = true;
      });
    });
  </script>
</body>
</html>