javascript - Code screws up when viewport changes -


i have following function makes 'up-btn' appear @ bottom of page when user scrolls 250px bottom ( , not on mobile)

html ( in head tags )

<script>  if ($(window).width() > 768) { $(window).scroll(function () {     if ($(window).scrolltop() + $(window).height() > ($(document).height() - 250)) {         $("#up-btn").fadein(500);     } else {         $("#up-btn").fadeout(500);     }    });  }; </script>

html (body)

<a id="up-btn" href="javascript:void(0);" onclick="scrolltop();"><i class="fa fa-chevron-up fa-lg"></i></a>

it works properly. however, when scale window mobile ceen size. or if window opens @ mobile size, etc. code doesn't work , button remains invisible.

wondering if there's changes code make more foolproof?

just remove if-statement:

<script>   $(window).on('scroll', function() {     if ($(window).scrolltop() + $(window).height() > ($(document).height() - 250)) {       $("#up-btn").fadein(500);     }     else {         $("#up-btn").fadeout(500);     }   }); </script>

when said, might consider debouncing function, avoid having recalculate time, eg. recalculate when scrolling stops.


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