https://www.daysjapan.net/wp-content/plugins/scroll-back-to-top/assets/js/scroll-back-to-top.js

1(function($){
2
3	$(function(){
4		if(typeof scrollBackToTop.autoFontSize !== 'undefined' && scrollBackToTop.autoFontSize){
5			$('.scroll-back-to-top-wrapper').textfill({ maxFontPixels: 36 });
6		}
7
8		$('.scroll-back-to-top-wrapper').on('click', function(){
9			if(typeof scrollBackToTop.scrollDuration !== 'undefined'){
10				scrollToElement("body", scrollBackToTop.scrollDuration, 0);
11			}
12		});
13
14		$(document).on( 'scroll', function(){
15
16			if ($(window).scrollTop() > 100) {
17				$('.scroll-back-to-top-wrapper').addClass('show');
18			} else {
19				$('.scroll-back-to-top-wrapper').removeClass('show');
20			}
21		});
22
23		if(typeof scrollBackToTop.visibilityDuration !== 'undefined' && scrollBackToTop.visibilityDuration){
24			$(window).on('scroll', function() {
25				clearTimeout($.data(this, 'sbttScrollTimer'));
26				$.data(this, 'sbttScrollTimer', setTimeout(function() {
27					$('.scroll-back-to-top-wrapper').removeClass('show');
28				}, scrollBackToTop.visibilityDuration));
29			});
30		}
31	});
32
33	function scrollToElement(selector, time, verticalOffset) {
34
35		time = typeof(time) != 'undefined' ? time : 1000;
36		verticalOffset = typeof(verticalOffset) != 'undefined' ? verticalOffset : 0;
37		element = $(selector);
38		offset = element.offset();
39		offsetTop = offset.top + verticalOffset;
40		$('html, body').animate({scrollTop: offsetTop}, parseInt(time), 'linear');
41	}
42
43	function isFullyVisible(el) {
44
45		if ( ! el.length ) {
46			return false;
47		}
48
49		if ( el instanceof jQuery ) {
50			el = el[0];
51		}
52
53		var top = el.offsetTop;
54		var left = el.offsetLeft;
55		var width = el.offsetWidth;
56		var height = el.offsetHeight;
57
58		while(el.offsetParent) {
59			el = el.offsetParent;
60			top += el.offsetTop;
61			left += el.offsetLeft;
62		}
63
64		return (
65			top >= window.pageYOffset &&
66				left >= window.pageXOffset &&
67				(top + height) <= (window.pageYOffset + window.innerHeight) &&
68				(left + width) <= (window.pageXOffset + window.innerWidth)
69			);
70	}
71
72	function isPartiallyVisible(el) {
73
74		if ( ! el.length ) {
75			return false;
76		}
77
78		if ( el instanceof jQuery ) {
79			el = el[0];
80		}
81
82		var top = el.offsetTop;
83		var left = el.offsetLeft;
84		var width = el.offsetWidth;
85		var height = el.offsetHeight;
86
87		while(el.offsetParent) {
88			el = el.offsetParent;
89			top += el.offsetTop;
90			left += el.offsetLeft;
91		}
92
93		return (
94			top < (window.pageYOffset + window.innerHeight) &&
95				left < (window.pageXOffset + window.innerWidth) &&
96				(top + height) > window.pageYOffset &&
97				(left + width) > window.pageXOffset
98			);
99	}
100})(jQuery);