function cngjpg(n){
var imgsrc = document.images[n].src;
if(imgsrc.indexOf("-on") < 0){
document.images[n].src = imgsrc.substring(0,imgsrc.length-4) + "-on.jpg";
}else{
document.images[n].src = imgsrc.substring(0,imgsrc.length-7) + ".jpg";
}
}
function cnggif(n){
var imgsrc = document.images[n].src;
if(imgsrc.indexOf("-on") < 0){
document.images[n].src = imgsrc.substring(0,imgsrc.length-4) + "-on.gif";
}else{
document.images[n].src = imgsrc.substring(0,imgsrc.length-7) + ".gif";
}
}
function cnimg(key, n){
var mapObj = key.parentNode;
var mapId = mapObj.getAttribute('id');
var imgObj = document.getElementsByTagName('img');
var imgNum = imgObj.length;
var usemap = '#' + mapId;
for (var i = 0; i < imgNum; i++){
if(imgObj[i].getAttribute('usemap') === usemap){
var imgPath = imgObj[i].src;
var ext = imgPath.substring(imgPath.lastIndexOf('.'), imgPath.length);
var suffix = '-' + n;
if(imgPath.indexOf(suffix) < 0){
imgObj[i].src = imgPath.substring(0, imgPath.length-ext.length) + suffix + ext;
}else{
imgObj[i].src = imgPath.substring(0, imgPath.length-(suffix.length + ext.length)) + ext;
}
break;
}
}
}