如何在倒计时中显示逗号？

function countdown() {
  var time = 60; // 倒计时时间，单位为秒
  var timer = setInterval(function() {
    var minutes = Math.floor(time / 60);
    var seconds = time % 60;
    
    // 判断是否需要显示逗号
    var displaySeconds = seconds;
    if (minutes > 0 && seconds < 10) {
      displaySeconds = "0" + seconds;
    }
    
    // 在页面中显示倒计时，并插入逗号
    document.getElementById("countdown").innerHTML = minutes + ":" + displaySeconds;
    
    time--;
    
    if (time < 0) {
      clearInterval(timer);
      document.getElementById("countdown").innerHTML = "倒计时结束";
    }
  }, 1000);
}