Javascript 如果身体有类在mp3声音淡入，否则淡出

如果主体具有fp-VIGING-0类，我尝试将mp3音量衰减为1 这怎么会不起作用，而且音量也不会改变？我该如何解决这个问题

代码：

var audio0 = document.getElementById('audio-0');
audio0.volume = 0;

setInterval( function(){
          if ($("body").hasClass("fp-viewing-0")) {
             audio0.animate({volume: 1}, 1000);
            }

else {
   audio0.animate({volume: 0}, 1000);
            }

 }, 100);

HTML

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亲切的问候

我已将jquery动画部分更改为手动淡入淡出。为此，我创建了一个淡入淡出时间和步骤计数来操纵淡入淡出效果

var audio0 = document.getElementById('audio-0');
audio0.volume = 0;

if ($("body").hasClass("fp-viewing-0")) {
     audio0.volume = 1; //max volume
     var fadeTime = 1500; //in milliseconds 
     var steps = 150; //increasing makes the fade smoother
     var stepTime = fadeTime/steps;
     var audioDecrement = audio0.volume/steps;

     var timer = setInterval(function(){
         audio0.volume -= audioDecrement; //fading out

         if (audio0.volume <= 0.03){ //if its already inaudible stop it
              audio0.volume = 0;
              clearInterval(timer); //clearing the timer so that it doesn't keep getting called
         }
     }, stepTime);
}

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非常感谢。如果if条件使音频淡出，我将如何处理else语句？我可以在else条件中添加什么使音频淡出？@Neths我不确定我是否理解你的问题。如果

正文中有
fp-viewing-0
类，则最后一个块中的
if
会使音频淡入淡出状态，否则它不会做任何事情。它以前也有
volume=0
。因此，最终的结果是，如果类存在，它会淡出音频，否则你将听不到任何声音。如果删除上面的
audio0.volume=0
，则如果该类存在，它将淡出，否则它将保持音频播放。
$("#audio-0").prop("volume", 0);


setInterval( function(){
          if ($("body").hasClass("fp-viewing-0")) {
            $("#audio-0").animate({volume: 1}, 3000);
            }

else {
   $("#audio-0").animate({volume: 0}, 3000);
            }

 }, 100);

var audio0 = document.getElementById('audio-0');
audio0.volume = 0;

if ($("body").hasClass("fp-viewing-0")) {
     audio0.volume = 1; //max volume
     var fadeTime = 1500; //in milliseconds 
     var steps = 150; //increasing makes the fade smoother
     var stepTime = fadeTime/steps;
     var audioDecrement = audio0.volume/steps;

     var timer = setInterval(function(){
         audio0.volume -= audioDecrement; //fading out

         if (audio0.volume <= 0.03){ //if its already inaudible stop it
              audio0.volume = 0;
              clearInterval(timer); //clearing the timer so that it doesn't keep getting called
         }
     }, stepTime);
}

function fadeAudio(audio, fadeTime, steps){ 
    audio.volume = 1; //max 
    steps = steps || 150; //turning steps into an optional parameter that defaults to 150
    var stepTime = fadeTime/steps;
    var audioDecrement = audio.volume/steps;

    var timer = setInterval(function(){
        audio.volume -= audioDecrement;

        if (audio.volume <= 0.03){ //if its already inaudible stop it
             audio.volume = 0;
             clearInterval(timer);
        }
    }, stepTime);
}

var audio0 = document.getElementById('audio-0');
audio0.volume = 0;
if ($("body").hasClass("fp-viewing-0")) {
    fadeAudio(audio0, 1500);
}