trigger function

function trigger (match, offset, func){
  var trigger_height = $(match).offset().top + offset;
  var element_height = $(match).height();
  $(window).on('scroll-tick', function() {
    var scrolltop = $(window).scrollTop();
    if(scrolltop > trigger_height && scrolltop < trigger_height + element_height){
      func();
    }
  });
}