Determine scroll direction and trigger a function depending on whether user is scrolling up or down

hide-show-medium-style-nav.js

var previousScroll = 0;

  $(window).scroll(function(){

    var currentScroll = $(this).scrollTop();

    if ( currentScroll < $(document).height() - $(window).height() ){
      // If we're scrolling down the page or at the top of the page
      if ( currentScroll > previousScroll || previousScroll < 300 || currentScroll < 300){
	   	// hide nav
        window.setTimeout(hideNav, 100);
	  // if scrolling up the page
      } else if ( currentScroll < previousScroll ) {
	  	//show the nav
	    window.setTimeout(showNav, 100);
	      
      } else {
	    // if we have other conditions, lets just hide the nav
        window.setTimeout(hideNav, 100);
        
      }
      // reset these vars to be equal until scrolling again
      previousScroll = currentScroll;
      
    }

  });
  function hideNav() {
    $("#fixed-header, #share-footer").removeClass("is-visible").addClass("is-hidden");
  }
  function showNav() {
    $("#fixed-header, #share-footer").removeClass("is-hidden").addClass("is-visible");
  }