https://mulberrygardens.org/Script%20Library/Global/inviewport.js?v=639246329620000000

1/*jslint browser: true, indent: 2 */
2(function ($) {
3  'use strict';
4  $.fn.inviewport = function (options) {
5    var settings = $.extend({
6      'minPercentageInView' : 25,
7      'standardClassName': 'in-view'
8    }, options);
9    this.each(function () {
10      var $this = $(this),
11        $win = $(window),
12        changed = false,
13        isVisible = function () {
14          var c = settings.className || settings.standardClassName,
15            min = (settings.threshold || settings.minPercentageInView) / 100,
16            xMin = $this.width() * min,
17            yMin = $this.height() * min,
18            winPosX = $win.scrollLeft() + $win.width(),
19            winPosY = $win.scrollTop() + $win.height(),
20            elPosX = $this.offset().left + xMin,
21            elPosY = $this.offset().top + yMin;
22          if (winPosX > elPosX && winPosY > elPosY) {
23            $this.addClass(c);
24          }
25        };
26      $win.on('ready', isVisible())
27        .on('resize scroll', function () {
28          changed = true;
29        });
30      setInterval(function () {
31        if (changed) {
32          changed = false;
33          isVisible();
34        }
35      }, 250);
36    });
37  };
38}(jQuery));