https://e-promag.pl/web/js/lazy-load.js

1$.fn.lazyLoad = function(margin) {
2    var _self = this;
3    var elements = [];
4
5    _self.each(function () {
6        if ($(this).data('src')) {
7            elements.push(this);
8        }
9    });
10
11    var lazyLoader = function () {
12        var windowHeight = $(window).height();
13        var windowScrollTop = $(window).scrollTop();
14        var i = 0;
15
16        while (i < elements.length) {
17            var element = $(elements[i]);
18            var offset = element.offset();
19            var height = element.outerHeight(true);
20
21            if (element.is(':hidden') && offset.top === 0 && offset.left === 0) {
22                i++;
23                continue;
24            }
25
26            if (offset.top - margin <= windowHeight + windowScrollTop &&
27                offset.top + height + margin >= windowScrollTop
28            ) {
29                element.attr('src', element.data('src'));
30                element.removeData( "src" );
31                elements.splice(i, 1);
32            } else {
33                i++;
34            }
35        }
36    };
37
38    $(window).on('scroll', lazyLoader);
39    $(window).on('resize', lazyLoader);
40    lazyLoader();
41
42    return _self;
43};