https://gsgundam.com/js/totop.js

1(function($) {
2    
3    // When to show the scroll link
4    // higher number = scroll link appears further down the page    
5    var upperLimit = 200; 
6        
7    // Our scroll link element
8    var scrollElem = $('#totop');
9    var scrollElem2 = $('#shortcut');
10    
11    // Scroll to top speed
12    var scrollSpeed = 500;
13    
14    // Show and hide the scroll to top link based on scroll position    
15    scrollElem.hide();
16    scrollElem2.hide();
17    $(window).scroll(function () {             
18        var scrollTop = $(document).scrollTop();        
19        if ( scrollTop > upperLimit ) {
20            $(scrollElem).stop().fadeTo(300, 1); // fade back in            
21            $(scrollElem2).stop().fadeTo(300, 1);
22        }else{        
23            $(scrollElem).stop().fadeTo(300, 0); // fade out
24            $(scrollElem2).stop().fadeTo(300, 0);
25        }
26    });
27
28    // Scroll to top animation on click
29    $(scrollElem).click(function(){ 
30        $('html, body').animate({scrollTop:0}, scrollSpeed); return false; 
31    });
32
33})(jQuery);