图片分左右不同点击效果不同的处理方法

<script>
function upNext(event){
var img = document.getElementById("imgId");
var lefturl = document.location;
var righturl = document.location;

var imgurl = righturl;
var width = (img.width==undefined) ? img.getAttribute("width") : img.width;
var x = (event.offsetX==undefined) ? getOffset(event).offsetX : event.offsetX;

function move(){
img.style.cursor = '';
if(event.offsetX<width/2){
if(lefturl != ''){
if(window.attachEvent){
img.style.cursor = 'url(images/left.cur),auto';
}else{
img.setAttribute("style","cursor:url(images/left.cur),auto;");
}
}
}else{
if(righturl != ''){
if(window.attachEvent){
img.style.cursor = 'url(images/right.cur),auto';
}else{
img.setAttribute("style","cursor:url(images/right.cur),auto;");
}
}
}

}

function up(){
if(event.offsetX<width/2){
if(lefturl != ''){
top.location = lefturl;
}
}else{
if(righturl != ''){
top.location = righturl;
}
}
}

if(window.attachEvent){
img.attachEvent("onmousemove",move);
img.attachEvent("onmouseup",up);
}else{
img.addEventListener("mousemove",move,false);
img.addEventListener("mouseup",up,false);
}

}

function getOffset(e){
var target = e.target;
if(target.offsetLeft == undefined){
target = target.parentNode;
}
var pageCoord = getPageCoord(target);
var eventCoord ={
x: window.pageXOffset + e.clientX,
y: window.pageYOffset + e.clientY
};
var offset ={
offsetX: eventCoord.x - pageCoord.x,
offsetY: eventCoord.y - pageCoord.y
};
return offset;
}
function getPageCoord(element)    {
var coord = {x: 0, y: 0};
while (element){
coord.x += element.offsetLeft;
coord.y += element.offsetTop;
element = element.offsetParent;
}
return coord;
}

if(window.attachEvent){
document.getElementById("imgId").attachEvent("onmouseover",upNext);
}else{
document.getElementById("imgId").addEventListener("mouseover",upNext,false);
}
</script>