jquery - Javascript syntax help for a back to top link that appears only on scroll up -


i have page set top link (in entire bar) slides down @ top of page, on scroll up.

i'm beginner javascript, have cobbled together, work (it shows on scroll up, unless we're 500px top, hides on scroll down), , uses code got here not check every pixel scrolled.

what want add if still scrolling once submenu, toplink should scroll off page again - don't need top once @ top.

i've gotten work adding second javascript script, know there must better way work in first call. second call uses window.scroll function i'm pretty sure wrong way it.

first script

// hide header on on scroll down var didscroll; var lastscrolltop = 0; var delta = 5; var submenu = $('#submenu').offset().top;  $(window).scroll(function(event){     didscroll = true; });  setinterval(function() {     if (didscroll) {         hasscrolled();         didscroll = false;     } }, 250);  function hasscrolled() {     var st = $(this).scrolltop();         // make sure scroll more delta     if(math.abs(lastscrolltop - st) <= delta)         return;      // if scroll down, add class .nav-up.      if (st > lastscrolltop && st ){         // scroll down          $('#backtotop').removeclass('nav-down').addclass('nav-up');          $(".toplink").fadeout("fast");       } else {         // scroll        if(st + $(window).height() < $(document).height() && st > 500) {         $('#backtotop').removeclass('nav-up').addclass('nav-down');         $(".toplink").fadein("slow");          }         }       lastscrolltop = st;  }

second script

    <script>     $(window).scroll (function ()    {var st = $(this).scrolltop();     var submenu = $('#submenu').offset().top;        if (st < submenu) {         $('#backtotop').removeclass('nav-down').addclass('nav-up');         $(".toplink").fadeout("fast");        }       });      </script>

fiddle html , css: https://jsfiddle.net/lu0jz3nc/11/

you should able in window scroll handler, of 1 global variable.

var min_delta = 5; var min_scrolltop = 500; var menu_height = $('#backtotop').height();  $('#backtotop').addclass('nav-up');  var lastscrolltop = 0; $(window).scroll(function (event) {     var scrolltop = $(window).scrolltop();     if (scrolltop > menu_height) {         if (scrolltop < lastscrolltop) { // scrolling             if (scrolltop > min_scrolltop) {                 if (scrolltop < (lastscrolltop - min_delta)) {                     $('#backtotop').removeclass('nav-up').addclass('nav-down');                     $(".toplink").fadein("slow");                     lastscrolltop = scrolltop;                 }             } else {                 lastscrolltop = scrolltop;             }         } else { // scrolling down             $('#backtotop').removeclass('nav-down').addclass('nav-up');             $(".toplink").fadeout("fast");             lastscrolltop = scrolltop;         }     } else {         $('#backtotop').removeclass('nav-down').addclass('nav-up');         $(".toplink").fadeout("fast");         lastscrolltop = scrolltop;     } });

notice lastscrolltop variable not updated when window has been scrolled down, past min_scrolltop, has not changed more min_delta.

jsfiddle


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