倒计时计时器:暂停按钮获胜't暂停或改回播放按钮

我在尝试暂停倒计时计时器时遇到问题。我正在努力做到这一点，所以在我点击播放按钮后，按钮变成了暂停按钮。但出于某种原因，它不会暂停。

我试图将id"pButton"更改为"pauseButton"，这是有效的，但我的暂停onclick功能似乎不会更改回pButton，有什么帮助吗？（clearinterval（timecounter），timercounter是一个全局可变变量，因此它可以访问它。）如果您需要查看，这里还有代码笔上的完整代码：http://codepen.io/freefora11/pen/eJdVjZ

//when play button is pressed
    if(document.getElementById("pButton")){
        document.getElementById("pButton").onclick=function(){
            //change the id of the button
            if(document.getElementById("pButton")){
                document.getElementById("pButton").id = "pauseButton";
            }
            //variables
            strMin = document.getElementById("test").innerHTML;
            var res = strMin.split(":",2);
            min = parseInt(res[0]);
            min= min * 60;
            var sec = parseInt(res[1]);
            timeInSeconds = min + sec;

            //set interval to start keeping track each second that has passed
            timeCounter = setInterval(function() {
              timeInSeconds--;
              // If we hit 0 seconds clear the timer
              if (timeInSeconds <= 0) {
                clearInterval(timeCounter);
              }
              // Display the current time
              displayTime();
            }, 1000);
        }
    }
    //when the pause button is clicked
    if(document.getElementById("pauseButton")){
        document.getElementById("pauseButton").onclick=function(){
            //stop the interval
            clearInterval(timeCounter);
            //change the id of the play button from pauseButton to pButton again
            if(document.getElementById("pauseButton")){
                document.getElementById("pauseButton").id ="pButton";
            }
        }
    }