https://bostonguide.com/engines//slideshow/js/slideshow.js

1var slideShowCurrent 	= 1;
2var t					= null;
3var slideShowOnext		= null;
4var slideShowOcurrent	= null;
5
6function gotoItemSlideshow(itemSS){
7	switch(itemSS){
8		case 'nextItemSS':
9			if(slideShowCurrent==totalItemsSS){
10				itemSS=1;
11			}else{
12				itemSS=slideShowCurrent+1;
13			}
14		break;		
15		case 'prevItemSS':
16			if(slideShowCurrent==1){
17				itemSS=totalItemsSS;
18			}else{
19				itemSS=slideShowCurrent-1
20			}
21		break;				
22	}
23	
24  
25	if(!document.images['slideShowItem'+itemSS].complete){
26		return false;
27	}
28	if(itemSS!=totalItemsSS){
29		if(!document.images['slideShowItem'+(itemSS+1)].complete){
30			return false;
31		}
32	}
33	
34	if(itemSS!=slideShowCurrent){
35		slideShowOcurrent	= $('idItemSS'+slideShowCurrent);	
36		nextItemSS			= 'idItemSS'+itemSS;	
37		slideShowOnext		= $(nextItemSS);	
38		document.getElementById('slideshow_content').style.background = 'url('+document.images['slideShowItem'+itemSS].src+')';		
39		document.getElementById('gotoItemSlideshow'+slideShowCurrent).className = '';	
40		document.getElementById('gotoItemSlideshow'+itemSS).className = 'active';					
41		effectCurrent();		
42		slideShowCurrent	= itemSS;
43	}
44	
45}
46
47function displayNextItemSS(obj){
48	slideShowOnext.style.display='block';
49}
50
51function initSlideshow(){
52    clearInterval(t);
53	
54    if(delaySS<1000){
55      delaySS=1000;
56    }
57	
58    t=setInterval("nextItemSlideshow()",delaySS);	
59}
60
61function nextItemSlideshow(){
62	gotoItemSlideshow('nextItemSS');
63}
64function prevItemSlideshow(){
65	gotoItemSlideshow('prevItemSS');
66}
67
68function stopSlideshow(){
69	clearInterval(t);
70}