純js實(shí)現(xiàn)倒計(jì)時(shí)功能

更新時(shí)間：2017年01月06日 11:06:14 作者：wangyuheng77

本文主要介紹了通過js實(shí)現(xiàn)頁面的倒計(jì)時(shí)功能的思路與方法，具有一定的參考價(jià)值，下面跟著小編一起來看下吧

通過js實(shí)現(xiàn)頁面的倒計(jì)時(shí)功能。

思路：傳入一個(gè)秒數(shù)c，c/60可以得到分鐘m, c%60可以得到顯示的秒數(shù)s，同理，再將m/60可是得到小時(shí)數(shù), m/%可以得到分鐘數(shù)。通過setInterval每次將總秒數(shù)-1，并將計(jì)算所得時(shí)間顯示到頁面上。

第一版的骯臟代碼如下，可以作為反面教材思考一下

<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、定義了眾多的全局變量，

2、沒有復(fù)用性，

3、setInterval容易導(dǎo)致隊(duì)列過多，結(jié)束事件如果是非阻塞事件，倒計(jì)時(shí)會(huì)繼續(xù)執(zhí)行出現(xiàn)負(fù)數(shù)，

4、不符合面向?qū)ο笏枷?。?！?/span>

針對(duì)缺陷1的解決方案是，定義一個(gè)函數(shù)，將相關(guān)全局變量放到函數(shù)內(nèi)部，使之成為局部變量

針對(duì)缺陷2：為函數(shù)指定參數(shù)，提高復(fù)用性。這里定義了3個(gè)參數(shù)vTimeLength為倒計(jì)時(shí)總秒數(shù)，showTagId為顯示到頁面元素的id， callback為倒計(jì)時(shí)結(jié)束后的回掉方法

針對(duì)缺陷3：用setTimeout替代setInterval

優(yōu)化后的代碼如下：

<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>

這里有一點(diǎn)需要注意

setTimeout(function(){countDownInner(vTimeLength);}, 1000);

第一次我將此句寫成了

setTimeout(countDownInner(vTimeLength), 1000);

結(jié)果函數(shù)直接執(zhí)行了，沒有等待1秒的時(shí)間。如果沒有入?yún)ⅲ?即setTimeout("countDownInner()", 1000); 則可正常執(zhí)行。

至于前面提到的不夠面向?qū)ο蟮娜毕荩?也是剛剛接觸，這里貼出代碼，希望能夠互相交流

<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>

一個(gè)難點(diǎn)是this的使用，在函數(shù)內(nèi)部， this是調(diào)用當(dāng)前函數(shù)范圍，所以setTimeout(function(){this.countDownInner(vTimeLength);}, 1000);會(huì)出現(xiàn)undefined。

解決方案是定義一個(gè)that變量接收外部函數(shù)的this指針，然后通過that即可調(diào)用外部域。

以上就是本文的全部?jī)?nèi)容，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作能帶來一定的幫助，同時(shí)也希望多多支持腳本之家！

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