``` <div id="timer"></div> var maxtime = 5 * 60; // function CountDown() { if (maxtime >= 0) { minutes = Math.floor(maxtime / 60); seconds = Math.floor(maxtime % 60); msg = "距离结束还有" + minutes + "分" + seconds + "秒"; document.all["timer"].innerHTML = msg; if (maxtime == 2 * 60){ alert("距离结束仅剩2分钟") }; --maxtime; } else{ clearInterval(timer); alert("免费上网时间到，请关注公众号获取更多时长!"); } } timer = setInterval("CountDown()", 1000); ```