Detect mobile javascript

gistfile1.js

function detectmob() { 
 if( navigator.userAgent.match(/Android/i)
 || navigator.userAgent.match(/webOS/i)
 || navigator.userAgent.match(/iPhone/i)
 || navigator.userAgent.match(/iPad/i)
 || navigator.userAgent.match(/iPod/i)
 || navigator.userAgent.match(/BlackBerry/i)
 || navigator.userAgent.match(/Windows Phone/i)
 ){
    return true;
  }
 else {
    return false;
  }
}

//ooooor

function detectmob() {
   if(window.innerWidth <= 800 && window.innerHeight <= 600) {
     return true;
   } else {
     return false;
   }
}