js计时功能

        //个位秒加
        function time4jia() {
            //分钟60为上限 所有加停止
            if (sz(a('time1').innerHTML) == 6) {
                return;
            }
            var m4 = sz(a('time4').innerHTML);//取个位秒
            if (m4 < 9) {
                //0-8秒 个位秒+1 并计算理论分
                a('time4').innerHTML = (m4 + 1);
                Llf();
            }
            else {
                //当前9秒 个位秒置0 
                a('time4').innerHTML = 0;
                //执行十位秒加1操作
                time3jia();
            }
        };

        //十位秒加
        function time3jia() {
            //分钟60为上限 所有加停止
            if (sz(a('time1').innerHTML) == 6) {
                return;
            }
            var m3 = sz(a('time3').innerHTML);//取十位秒
            if (m3 < 5) {
                //0-4秒 十位秒+1 并计算理论分
                a('time3').innerHTML = (m3 + 1);
                Llf();
            }
            else {
                //当前5秒 十位秒置0 
                a('time3').innerHTML = 0;
                //执行个位分加1操作
                time2jia();
            }
        };

        //个位分加
        function time2jia() {
            //分钟60为上限 所有加停止
            if (sz(a('time1').innerHTML) == 6) {
                return;
            }
            var m2 = sz(a('time2').innerHTML);//取个位分
            if (m2 < 9) {
                //0-8分 个位分+1 并计算理论分
                a('time2').innerHTML = (m2 + 1);
                Llf();
            }
            else {
                //当前9分 个位分置0 
                a('time2').innerHTML = 0;
                //执行十位分加1操作
                time1jia()
            }
        };

        //十位分加
        function time1jia() {
            //分钟60为上限 所有加停止
            if (sz(a('time1').innerHTML) == 6) {
                return;
            }
            var m1 = sz(a('time1').innerHTML);//取十位分
            if (m1 < 6) {
                //0-5分 十位分+1 
                a('time1').innerHTML = (m1 + 1);
                if (sz(a('time1').innerHTML) == 6) {
                    //十位分+1后为上限6 则其它归0
                    a('time4').innerHTML = 0;
                    a('time3').innerHTML = 0;
                    a('time2').innerHTML = 0;
                }
            }
            Llf();//最后计算理论分
        };

        //个位秒减
        function time4jian() {
            var m4 = sz(a('time4').innerHTML);//取个位秒
            if (m4 > 0) {
                //个位秒大于0 则-1 并计算理论分
                a('time4').innerHTML = (m4 - 1);
                Llf();
            }
            else {
                //个位秒为0时 减成9 再执行十位秒减1操作
                a('time4').innerHTML = 9;
                time3jian();
            }
        };

        //十位秒减
        function time3jian() {
            var m3 = sz(a('time3').innerHTML);//取十位秒
            if (m3 > 0) {
                //十位秒大于0 则-1 并计算理论分
                a('time3').innerHTML = (m3 - 1);
                Llf();
            }
            else {
                //十位秒为0时 减成5 再执行个位分减1操作
                a('time3').innerHTML = 5;
                time2jian();
            }
        };

        //个位分减
        function time2jian() {
            var m2 = sz(a('time2').innerHTML);//取个位分
            if (m2 > 0) {
                //个位分大于0 则-1 并计算理论分
                a('time2').innerHTML = (m2 - 1);
                Llf();
            }
            else {
                //个位分为0时 减成9 再执行十位分减1操作
                a('time2').innerHTML = 9;
                time1jian();
            }
        };

        //十位分减
        function time1jian() {
            var m1 = sz(a('time1').innerHTML);//取十位分
            if (m1 > 0) {
                //十位分大于0 则-1 并计算理论分
                a('time1').innerHTML = (m1 - 1);
            }
            else {
                //当十位分为0时 再减 则全部归0
                a('time4').innerHTML = 0;
                a('time3').innerHTML = 0;
                a('time2').innerHTML = 0;
                a('time1').innerHTML = 0;
            }
            Llf();//最后计算理论分
        };

        //循环事件标记变量
        var int = 0;

        //倒计时启动
        function qidong() {
            time4jian();
            int = self.setInterval("time4jian()", 1000);
            a('startbtn').style.display = "none";
            a('stopbtn').style.display = "";
        };

        //倒计时停止
        function tingzhi() {
            window.clearInterval(int);
            a('startbtn').style.display = "";
            a('stopbtn').style.display = "none";
        };

<table border="0" width="100%" cellpadding="0" style="border-collapse: collapse" height="100%">
                            <tr>
                                <td align="right" valign="bottom" class="auto-style1"></td>
                                <td align="center" valign="bottom" class="auto-style1">
                                    <input type="button" value="+" class="shengyu" onClick="time2jia();"></td>
                                <td align="center" valign="bottom" class="auto-style1">
                                    <input type="button" value="+" class="shengyu" onClick="time3jia();"></td>
                                <td align="left" valign="bottom" class="auto-style4">
                                    <input type="button" value="+" class="shengyu" onClick="time4jia();"></td>
                            </tr>
                            <tr>
                                <td align="right" class="auto-style1">
                                    <span id="time1" class="daojishi">2</span>
                                </td>
                                <td align="center" class="auto-style1">
                                    <span id="time2" class="daojishi">0</span>
                                </td>
                                <td align="left" class="auto-style1">
                                    <span class="daojishi">:</span>
                                    <span id="time3" class="daojishi">0</span>
                                </td>
                                <td align="left" class="auto-style4">
                                    <span id="time4" class="daojishi">0</span>
                                </td>
                            </tr>
                            <tr>
                                <td align="right" valign="top" class="auto-style1"></td>
                                <td align="center" valign="top" class="auto-style1">
                                    <input type="button" value="-" class="shengyu" onClick="time2jian();"></td>
                                <td align="center" valign="top" class="auto-style1">
                                    <input type="button" value="-" class="shengyu" onClick="time3jian();"></td>
                                <td align="left" valign="top" class="auto-style4">
                                    <input type="button" value="-" class="shengyu" onClick="time4jian();"></td>
                            </tr>
                        </table>