which is best way detect mobile device javascript or media?

Question

which is best way detect mobile device javascript or media query? 

     javascript       

              $(document).ready(function () {

                     alert(detectmob());

               });

function detectmob() {

               if (window.innerWidth <= 800 && window.innerHeight <= 600) {

                              return false;

                 } else {

                           $(".blackbutton").addClass("ismobileblockbutton");

                           $('.ismobileblockbutton').removeAttr("href")

                        }

                  }

 

media query

@media screen and (min-width:600px) and (max-width: 800px) {

.tbms {

height: 60px !important;

}

}