如何判断 ie 是否支持 html5 的 audio 元素？如果支持执行 A.JS 代码，如果不支持则执行 B.JS

var audio = document.getElementById("audio");
audio.loop = false;
window. onload = function(){//页面加载完毕后调用
var ass = document.getElementById('audio').duration;//如果当前时常为NaN赋值
if(this.isNaN(ass)){
var ids = '[dance:id]'-2;
//this.self.location='127.0.0.1/ceshi/index.php/dance/play/id/'+ids;
}else{
var ids = '[dance:id]'-1;
};
audio.addEventListener('ended', function () {

this.self.location='127.0.0.1/ceshi/index.php/dance/play/id/'+ids;
}, false);
}