时间:2021-07-01 10:21:17 帮助过:10人阅读
通过js实现页面的倒计时功能。
思路: 传入一个秒数c,c/60可以得到分钟m, c%60可以得到显示的秒数s,同理,再将m/60可是得到小时数, m/%可以得到分钟数。通过setInterval每次将总秒数-1,并将计算所得时间显示到页面上。
第一版的肮脏代码如下, 可以作为反面教材思考一下
<html> <head> <title>Tomato</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <script type="text/javascript"> var vTimeLength = 5; var vHour; var vMinutes; var vSeconds; var vRemainingTime; function countDown(){ vTimeLength = vTimeLength - 1; vMinutes = Math.floor(vTimeLength/60); vSeconds = Math.floor(vTimeLength%60); if (vMinutes >= 60){ vHour = Math.floor(vMinutes/60); var vMinutesNew = Math.floor(vMinutes%60); vRemainingTime = vHour + ":" + vMinutesNew + ":" + vSeconds; } else { vRemainingTime = vMinutes + ":" + vSeconds; } document.getElementById("div_countDown").innerHTML = vRemainingTime; if (vTimeLength < 1) { alert('do sth'); } } </script> </head> <body> <div id="div_countDown"></div> <script type="text/javascript"> setInterval("countDown()", 1000); </script> </body> </html>
缺陷:
1、定义了众多的全局变量,
2、没有复用性,
3、setInterval容易导致队列过多, 结束事件如果是非阻塞事件, 倒计时会继续执行出现负数,
4、不符合面向对象思想。。。
针对缺陷1的解决方案是, 定义一个函数, 将相关全局变量放到函数内部,使之成为局部变量
针对缺陷2:为函数指定参数,提高复用性。 这里定义了3个参数vTimeLength为倒计时总秒数,showTagId为显示到页面元素的id, callback为倒计时结束后的回掉方法
针对缺陷3:用setTimeout替代setInterval
优化后的代码如下:
<html> <head> <title>countdown</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <script type="text/javascript"> function countDown(vTimeLength, showTagId, callback) { var vHour; var vMinutes; var vMinutesNew var vSeconds; var vRemainingTime; function countDownInner(vTimeLength){ vMinutes = Math.floor(vTimeLength/60); vSeconds = Math.floor(vTimeLength%60); if (vMinutes >= 60){ vHour = Math.floor(vMinutes/60); vMinutesNew = Math.floor(vMinutes%60); vRemainingTime = vHour + ":" + vMinutesNew + ":" + vSeconds; } else { vRemainingTime = vMinutes + ":" + vSeconds; } document.getElementById(showTagId).innerHTML = vRemainingTime; vTimeLength = vTimeLength - 1; if (vTimeLength > 0) { setTimeout(function(){countDownInner(vTimeLength);}, 1000); } else { callback(); } } countDownInner(vTimeLength); } </script> </head> <body> <div id="div_countDown"></div> <script type="text/javascript"> countDown(5, "div_countDown", function(){alert('do sth');}); </script> </body> </html>
这里有一点需要注意
setTimeout(function(){countDownInner(vTimeLength);}, 1000);
第一次我将此句写成了
setTimeout(countDownInner(vTimeLength), 1000);
结果函数直接执行了, 没有等待1秒的时间。如果没有入参, 即setTimeout("countDownInner()", 1000); 则可正常执行。
至于前面提到的不够面向对象的缺陷, 也是刚刚接触, 这里贴出代码,希望能够互相交流
<html> <head> <title>count_down</title> <script type="text/javascript"> var countDown = { flag: true, hour: 0, minutes: 0, minutesNew: 0, seconds: 0, show: 0, current: 0, length: 0, showTagId: null, // callback: null, countDownInner: function(vTimeLength){ if (!this.flag) { return; } var that=this; this.current = vTimeLength; minutes = Math.floor(vTimeLength/60); seconds = Math.floor(vTimeLength%60); if (minutes >= 60){ hour = Math.floor(minutes/60); minutesNew = Math.floor(minutes%60); show = hour + ":" + minutesNew + ":" + seconds; } else { show = minutes + ":" + seconds; } document.getElementById(this.showTagId).innerHTML = show; vTimeLength = vTimeLength - 1; if (vTimeLength > 0) { setTimeout(function(){that.countDownInner(vTimeLength);}, 1000); } else { setTimeout(function(){that.callback();}, 1000); } }, run: function(vTimeLength, showTagId, callback) { if (!this.flag) { this.flag = true; this.countDownInner(this.current); } else if (showTagId) { this.length = vTimeLength; this.showTagId = showTagId; this.callback = callback; this.countDownInner(vTimeLength); } }, stop: function(){ this.flag = false; }, restart: function(){ this.flag = true; this.countDownInner(this.length); } }; function countDownStart() { countDown.run(); } function countDownStop() { countDown.stop(); } </script> </head> <body> <div id="div_countDown"></div> <script type="text/javascript"> countDown.run(5, 'div_countDown',function(){alert('12')}); </script> <span> <button onclick="countDownStart();">start</button> <button onclick="countDownStop();">stop</button> </span> </body> </html>
一个难点是this的使用, 在函数内部, this是调用当前函数范围,所以setTimeout(function(){this.countDownInner(vTimeLength);}, 1000);会出现undefined。
解决方案是定义一个that变量接收外部函数的this指针,然后通过that即可调用外部域。
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