问Jquery倒计时:如何在倒计时的不同时刻进行回调？

EN

$(function() {
    //Initialization
    var minutes = 30;
    var seconds = 0;
    //Make sure your div exists
    var countDownContext = $("#divCountdown");
    //Showing things initially
    countDownContext.text(minutes + ":" + seconds);
    //15 seconds
    var initialTime = 15;
    //We store the interval to be able to stop the repetition later
    var myInterval = setInterval(function() {
        //Are we still inside those 15 seconds at the start?
        if (initialTime > 0) {
            //Was this the last second?
            if (--initialTime === 0) {
                //Then hide
                countDownContext.hide();
            }
        }
        //We decrease seconds and check whether it, before decreasing was 0
        if (seconds-- === 0) {
            //If it was, then we decrease a minute and set seconds to 59
            minutes--;
            seconds = 59;
        }
        //Refresh inner text
        countDownContext.text(minutes + ":" + seconds);
        //Is the last minute reached?
        if ((minutes === 1) && (seconds === 0)) {
            //Then show
            countDownContext.show();
        }
        //Is the time expired?
        if ((minutes <= 0) && (seconds <= 0)) {
            //Then alert about it
            alert("Your time is up");
            //And clear the interval
            clearInterval(myInterval);
        }
    }, 1000);
});

$("#divCountdown")
   .countdown(timeToExpire, function (event) {
      $(this).text(
        event.strftime('%M:%S')
      );
}).on('update.countdown',function(event) {
   //check event.offset.totalMinutes value to show/hide object
}).on('finish.countdown',function(event){
   //display alert
});

var $countdown = $("#divCountdown"),
    countdownMinutes = 30,
    timeStart = new Date().getTime(),
    timeEnd = timeStart + countdownMinutes * 60 * 1000;

$countdown
    .countdown(timeEnd, function (e) {

        var now = e.timeStamp,
            secondsElapsed = Math.floor((now - timeStart) / 1000),
            secondsRemaining = Math.ceil((timeEnd - now) / 1000);

        $countdown.text(e.strftime('%M:%S'));

        switch (secondsElapsed) {
            case 15:
                $countdown.hide();
                break;
        }

        switch (secondsRemaining) {
            case 60:
                $countdown.show();
                break;
        }
    })
    .on('finish.countdown', function (e) {
        setTimeout(function () {
            alert('boom');
        });
    });