如何实现节点图标没展开时图标是+号 ,展开后图标变为-号
如何实现节点图标没展开时图标是+号  展开后图标变为-号  是要用js控制吗  如何实现 谢谢各位
页面如下
<html>
<head>
<meta http-equiv="Content-Language" content="zh-cn">
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>数据展现</title>
<style type="text/css">
.spanstyle {
COLOR: #00cccc; FONT-FAMILY: 宋体; FONT-SIZE: 10pt; POSITION: absolute; TOP: -50px; VISIBILITY: visible
}
</style>     
<script language="JavaScript1.2">
scores = new Array(20);var numTotal=0;NS4 = (document.layers) ? 1 : 0;IE4 = (document.all) ? 1 : 0;ver4 = (NS4 || IE4) ? 1 : 0;if (ver4) {    with (document) {        write
("<STYLE TYPE='text/css'>");        if (NS4) {            write(".parent {position:absolute; visibility:visible}");            write(".child {position:absolute;  
visibility:visible}");            write(".regular {position:absolute; visibility:visible}")        }        else {            write(".child {display:none}")        }         
write("</STYLE>");    }}function getIndex(el) {    ind = null;    for (i=0; i<document.layers.length; i++) {        whichEl = document.layers[i];        if (whichEl.id == el) {   
           ind = i;            break;        }    }    return ind;}function arrange() {    nextY = document.layers[firstInd].pageY +document.layers[firstInd].document.height;     
for (i=firstInd+1; i<document.layers.length; i++) {        whichEl = document.layers[i];        if (whichEl.visibility != "hide") {            whichEl.pageY = nextY;             
nextY += whichEl.document.height;        }    }}function initIt(){    if (!ver4) return;    if (NS4) {        for (i=0; i<document.layers.length; i++) {            whichEl =  
document.layers[i];            if (whichEl.id.indexOf("Child") != -1) whichEl.visibility = "hide";       }        arrange();    }    else {        divColl = document.all.tags
("DIV");        for (i=0; i<divColl.length; i++) {            whichEl = divColl(i);            if (whichEl.className == "child") whichEl.style.display = "none";        }    }}
function expandIt(el) {	if (!ver4) return;    if (IE4) {        whichEl1 = eval(el + "Child");		for(i=1;i<=numTotal;i++){			whichEl = eval(scores[i]  
+ "Child");			if(whichEl!=whichEl1) {				whichEl.style.display = "none";			}		}        whichEl1 = eval(el +  
"Child");        if (whichEl1.style.display == "none") {            whichEl1.style.display = "block";        }        else {            whichEl1.style.display = "none";        }  
    }    else {        whichEl = eval("document." + el + "Child");		for(i=1;i<=numTotal;i++){			whichEl = eval("document." + scores[i] +  
"Child");			if(whichEl!=whichEl1) {				whichEl.visibility = "hide";			}		}        if (whichEl.visibility  
== "hide") {            whichEl.visibility = "show";        }        else {            whichEl.visibility = "hide";        }        arrange();    }}onload = initIt;
</script>
<style>
<!--
.line3 {
	BORDER-RIGHT: #b1e397 1px solid; BORDER-TOP: #b1e397 1px solid; BORDER-LEFT: #b1e397 1px solid; BORDER-BOTTOM: #b1e397 1px solid
}
-->
</style>
</head>
<body >
<div id='KB1Parent' class='parent'>
		<b><font size="6" color="