h5网页跳转到app，若未安装app，则跳转app下载页面

        if(isAndroid){     
                android();
              function android(){
                    var ifr = document.createElement("iframe");
                  ifr.src = ""; 
                  //app地址
                  ifr.style.display = "none"; 
                  document.body.appendChild(ifr);     
                  window.setTimeout(function(){
                    document.body.removeChild(ifr);
                    window.location.href = "";
                    //app下载地址
                   },500)
             }      
            }
          
           if(isiOS){ 
               ios()
             function ios(){
                   window.location.href="";
                    //app地址
                   window.setTimeout(function(){
                      window.location.href = ""; 
                      /***下载app的地址***/
                   },2000)
              }
           }