https://www.jeu-de-puzzle.net/js/theme_bg_1_00.js

1var bg_image_list;
2var bg_preload_img=new Array();
3var bg_loaded=new Array();
4var bg_timer_id;
5var bg_renew_id;
6var bg_curr_count=0;
7var bg_base_href;
8var bg_image_id=0;
9function theme_bg_preload_image_list(base_href,bg_image_list_str){
10	bg_base_href=base_href;
11	bg_image_list=bg_image_list_str.split(',');
12	bg_load_images();
13}
14function bg_load_images(){
15	var i;
16	for(i=0;i<bg_image_list.length;i++){
17		bg_preload_img[i]=new Image();
18		bg_preload_img[i].src=bg_base_href+bg_image_list[i];
19	}
20	for(i=0;i<bg_preload_img.length;i++){
21		bg_loaded[i]=false;
22	}
23	bg_timer_id=setInterval("bg_check_load()",250);
24	bg_renew_id=setInterval("bg_change_image()",6000);
25}
26function bg_check_load(){
27	var i;
28	if (bg_curr_count==bg_preload_img.length){
29		clearInterval(bg_timer_id);
30		bg_curr_count=0;
31		return;
32	}
33  	for(i=0;i<=bg_preload_img.length;i++){
34  		if((bg_loaded[i]==false)&&(bg_preload_img[i].complete)){
35  			bg_loaded[i]=true;
36  			bg_curr_count++;
37  		}
38  	}
39}
40
41function bg_change_image(){
42	bg_image_id++;
43	if(bg_image_id>=bg_image_list.length){
44		bg_image_id=0;
45	}
46	document.getElementById('theme_content_div').style.backgroundImage='url('+bg_base_href+bg_image_list[bg_image_id]+')';
47}
48
49function bg_stop_renew(){
50	bg_image_id=0;
51	clearInterval(bg_renew_id);
52}