function downloadApp(){
 var u = navigator.userAgent; 
 var ua = navigator.userAgent.toLowerCase(); 
 var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Adr') > -1; //android终端 
  var isiOS = !!u.match(/\(i[^;]+;( U;)"micromessenger") { //微信内置浏览器
  $(".download a").click(function(){
   window.location.href='http://a.app.qq.com/o/simple.jsp".download a").click(function(){
    window.location.href='https://itunes.apple.com/cn/app/应用名'
   });
  }else if(isAndroid){
   $(".download a").click(function(){
    window.location.href='http://a.app.qq.com/o/simple.jsp".download a").click(function(){
    window.location.href='应用链接'

   });

  }

 }

  

 }