纯js实现倒计时功能
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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