html - Want to load javascript for mobile devices only

Question

I want to show these 4 buttons in a row in desktop mode and show carousel like this only for mobile view The first pic is for mobile view and the second pic is for pc view Here is the link to my code https://jsfiddle.net/FODraciel/wehc8ryv/4/ I am trying with javascript and tried some steps which were set width technique but it does not work. Any idea of how to do it? I have tried some steps like this

window.onload=function(){
w = document.documentElement.clientWidth || document.body.clientWidth || window.innerWidth;
var targetWidth = 768;
if ( w >= targetWidth) {     
  //Add your javascript for screens wider than or equal to 768 here
}
else {
  //Add your javascript for screens smaller than 768 here
}  

};

Answer 1

等待大神答复