向Java倒数计时器添加分钟还是秒？

我有一个JavaScript倒数计时器。我需要做的是能够在倒数计时器运行时向计时器添加1分钟或几秒钟！

例如：如果我将分钟设置为1分钟并按“开始”按钮，则倒数计时器将按原样启动，但如果我在计时器运行时再增加一分钟，即32秒时，则不会添加该值到当前数字，它将继续倒计时添加的前1分钟的剩余时间，并且由于某种原因，它只会加快倒数的速度！

希望我不要让你们感到困惑。这是代码：

<form>
Minutes: <input type="text" id="mns" name="mns" value="0" size="3" maxlength="3" /> &nbsp; &nbsp; Seconds: <input type="text" id="scs" name="scs" value="0" size="2" maxlength="2" /><br/>
<input type="button" id="btnct" value="START" onclick="countdownTimer()"/>
</form>
Countdown Timer: &nbsp; <span id="showmns">00</span>:<span id="showscs">00</span>
<script type="text/javascript"><!--
    /* Function to display a Countdown timer with starting time from a form */
// sets variables for minutes and seconds
var ctmnts = 0;
var ctsecs = 0;
var startchr = 0;       // used to control when to read data from form

function countdownTimer() {
  // http://coursesweb.net/javascript/
  // if $startchr is 0, and form fields exists, gets data for minutes and seconds, and sets $startchr to 1
  if(startchr == 0 && document.getElementById('mns') && document.getElementById('scs')) {
    // makes sure the script uses integer numbers
    ctmnts = parseInt(document.getElementById('mns').value) + 0;
    ctsecs = parseInt(document.getElementById('scs').value) * 1;

    // if data not a number, sets the value to 0
    if(isNaN(ctmnts)) ctmnts = 0;
    if(isNaN(ctsecs)) ctsecs = 0;

    // rewrite data in form fields to be sure that the fields for minutes and seconds contain integer number
    document.getElementById('mns').value = ctmnts;
    document.getElementById('scs').value = ctsecs;
    startchr = 1;
  }

  // if minutes and seconds are 0, sets $startchr to 0, and return false
  if(ctmnts==0 && ctsecs==0) {
    startchr = 0;
    document.getElementById('btnct').removeAttribute('disabled');     // remove "disabled" to enable the button

    /* HERE YOU CAN ADD TO EXECUTE A JavaScript FUNCTION WHEN COUNTDOWN TIMER REACH TO 0 */

    return false;
  }
  else {
    // decrease seconds, and decrease minutes if seconds reach to 0
    ctsecs--;
    if(ctsecs < 0) {
      if(ctmnts > 0) {
        ctsecs = 59;
        ctmnts--;
      }
      else {
        ctsecs = 0;
        ctmnts = 0;
      }
    }
  }

  // display the time in page, and auto-calls this function after 1 seccond
  document.getElementById('showmns').innerHTML = ctmnts;
  document.getElementById('showscs').innerHTML = ctsecs;
  setTimeout('countdownTimer()', 1000);
}
//-->
</script>

任何帮助，将不胜感激。

这是小提琴