https://www.parc-naturel-chevreuse.fr/themes/custom/chevreuse/js/views/ScrollHitView.js?tm7vqo

1var ScrollHitView = Backbone.View.extend({
2  initialize: function(tag){
3    this.$tag = $(tag);
4    this.$tag.removeClass('show');
5    $(window).bind('resize', this.onResize.bind(this));
6    this.onResize();
7    $(window).bind('scroll', this.onScroll.bind(this));
8    this.onScroll();
9  },
10  onResize: function() {
11    this.topPosition = this.$tag.offset().top;
12    this.height = this.$tag.height();
13    this.windowHeight = $(window).height();
14  },
15  onScroll: function() {
16    var adjustement;
17    if ($(window).width() < 768) {
18      adjustement = 220;
19    }
20    else {
21      adjustement = $(window).height() / 2 - 180;
22    }
23    if ((this.topPosition - adjustement) < ($(window).scrollTop() + this.windowHeight / 2)) {
24      this.show();
25    }
26    else {
27      this.hide();
28    }
29  },
30  show: function() {
31    this.$tag.addClass('show');
32  },
33  hide: function() {
34    this.$tag.removeClass('show');
35  }
36});