I have this function in my < head > which puts a 'shrink' class onto 'header' class when scrolled 100px.
$(function(){
 var shrinkHeader = 100;
$(window).scroll(function() {
var scroll = getCurrentScroll();
  if ( scroll >= shrinkHeader ) {
       $('header').addClass('shrink');
    }
    else {
        $('header').removeClass('shrink');
    }
});
I want it not to work when the screen is mobile screen size. But I'm not sure how to adjust it for that.
EDIT - Looking for a responsive option (screen size shrinks/grows)
 
     
     
     
     
    