我下面有一个秒表代码，一开始运行的是ss：ms（秒.毫秒）格式，当它达到60秒以上时，我希望它运行的是mm：ss.ms（分钟：秒.毫秒）格式，这里是我的代码

let sec = 0;
let min = 0;
let millisecond = 0;
const stopwatch = document.getElementById("stopwatch");
function stopwatchStart() {
    sec = parseInt(sec);
    min = parseInt(min);
    millisecond = parseInt(millisecond);

    millisecond = millisecond + 1;

    if (millisecond == 100) {
      sec = sec + 1;
      millisecond = 0;
    }

    stopwatch.innerHTML = sec + '.' + millisecond;

    if (sec === 60) {
      min = min + 1;
      sec = 0;
      // how do i make it run on MM:SS:MS format
    };

    setTimeout("stopwatchStart()", 10);
}

我尝试了这段代码，但不起作用（不改变秒表的innerHTML）

 if (sec === 60) {
      min = min + 1;
      sec = 0;
      stopwatch.innerHTML = min  + ":" + sec + "." + millisecond;
    };