如何在音频HTML5上淡入/淡出(how to have fade in/out on audio HTML5)

 你必须注意HTMLAudioElement（ $('#musicBeat')[0] ）和jQuery Object（ $('#musicBeat') ）之间的$('#musicBeat') 。 
 
 play是HTMLAudioElement的一个方法，所以你必须通过它访问它（就像你一样），但.animate是一个jQuery方法，只能在jQuery对象上调用。 
 
 而且你必须指定newVolume（不能将其留空）。 
 
var beepTwo = $("#musicBeat");
beepTwo[0].play();

$("#dan").click(function() {  
    if (beepTwo[0].paused == false) {
        beepTwo.animate({volume: 0}, 2000, 'swing', function() {
            // really stop the music 
            beepTwo[0].pause();   
        });
     } else {
         beepTwo[0].play();  
         beepTwo.animate({volume: 1}, 2000);
     }
});

You have to watch out for the difference between the HTMLAudioElement ($('#musicBeat')[0]) and the jQuery Object ($('#musicBeat')).
 
play is a method of the HTMLAudioElement, so you'll have to access it over that (as you did), but .animate is a jQuery method and can only be called on a jQuery object.
 
And you have to specify newVolume (can't leave it empty).
 
var beepTwo = $("#musicBeat");
beepTwo[0].play();

$("#dan").click(function() {  
    if (beepTwo[0].paused == false) {
        beepTwo.animate({volume: 0}, 2000, 'swing', function() {
            // really stop the music 
            beepTwo[0].pause();   
        });
     } else {
         beepTwo[0].play();  
         beepTwo.animate({volume: 1}, 2000);
     }
});