兼容各种浏览器的背景音乐循环播放的JS代码，具体代码如下：

var bgSoundFile = "http://www.phpernote.com/style/bgsound.mp3";

if (navigator.userAgent.toLowerCase().indexOf("msie") != -1) {
    document.write('<bgsound src="' + bgSoundFile + '" loop="-1">');
} else if (navigator.userAgent.toLowerCase().indexOf("firefox") != -1) {
    document.write('<object data="' + bgSoundFile + '" type="application/x-mplayer2" width="0" height="0"><param name="filename" value="' + bgSoundFile + '"><param name="autostart" value="1"><param name="playcount" value="infinite"></object>');
} else {
    document.write('<audio src="' + bgSoundFile + '" autoplay="autoplay" loop="loop"><object data="' + bgSoundFile + '" type="application/x-mplayer2" width="0" height="0"><param name="filename" value="' + bgSoundFile + '"><param name="autostart" value="1"><embed height="2" width="2" src="' + bgSoundFile + '" pluginspage="http://www.apple.com/quicktime/download/" type="video/quicktime" controller="false" controls="false" autoplay="true" autostart="true" loop="true" bgcolor="#000000"></embed></object></audio>');
}