<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title> New Document </title>
<meta name="Generator" content="EditPlus">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<script language="JavaScript">
<!--
var ii = 0;
function boxnum(){
var box = document.getElementsByName("c");
for(var i=0;i<box.length;i++){
box[i].onclick = function chk(){
if(this.checked && ii <= 5) ii += 1;
if(! this.checked) ii -= 1;
if(ii>5){ ii -=1; this.checked = false;alert('最多不能超多5个主营项目！请重新选择！');}
}
}
}
window.onload = boxnum;
//-->
</script>
</head>
<body>
<table cellspacing="0" border="1" width="200" >
<tr>
<td><input type="checkbox" name="c"></td>
<td><input type="checkbox" name="c"></td>
<td><input type="checkbox" name="c"></td>
</tr>
<tr>
<td><input type="checkbox" name="c"></td>
<td><input type="checkbox" name="c"></td>
<td><input type="checkbox" name="c"></td>
</tr>
</body>
</html>
第二种方法
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
<script>
function boxnum(obj){
}
function checknum(){
var e,srcE
e=window.event?window.event:e;
srcE=e.srcElement?e.srcElement:e.target;
if(!srcE)return;
if(String(srcE.tagName).toLowerCase()!="input"||String(srcE.type).toLowerCase()!="checkbox")return;
var box = document.form1.elements['checkbox3'];
var ii = 0
for(var i=0;i<box.length;i++){
if(box[i].checked){ii++;}
}
if(ii>5){
alert('最多不能超多5个主营项目！请重新选择！');
srcE.checked=false;
}
}
document.onkeydown=document.onchange=document.onclick=checknum;
</script>
</head>
<body>
<form id="form1" name="form1" method="post" action="">
<table width="520" height="221" border="1">
<tr>
<td><label>
<input type="checkbox" name="checkbox3" value="checkboxa" />
1
<input type="checkbox" name="checkbox3" value="checkboxaa" />
2
<input type="checkbox" name="checkbox3" value="checkboxaaa" />
3
<input type="checkbox" name="checkbox3" value="checkboxaaaa" />
4
<input type="checkbox" name="checkbox3" value="checkboxcv" />
5
<input type="checkbox" name="checkbox3" value="checkboxcvb" />
6
<input type="checkbox" name="checkbox3" value="checkboxcvbcvb" />
7
<input type="checkbox" name="checkbox3" value="checkboxcvbcvbcv" />
8
<input type="checkbox" name="checkbox3" value="checcvb" />
9
<input type="checkbox" name="checkbox3" value="checvb" />
10
<input type="checkbox" name="checkbox3" value="chcvbox" />
<input type="checkbox" name="checkbox3" value="chcvbcvbox" />
<input type="checkbox" name="checkbox3" value="ccvbcvbcvox" />
</label></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td><input type="button" name="Submit" value="按钮" onclick="boxnum('checkbox3')" /></td>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td> </td>
<td> </td>
</tr>
</table>
</form>
</body>
</html>
<form method="post" action="" name="form1" id="form1">
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
<input type="checkbox" name="a" />
</form>
<script language="javascript" type="text/javascript">
var m_count = 0;
document.getElementById("form1").onclick = function(e){
ele = (document.all)?window.event.srcElement:e.target;
if (ele.nodeName.toLowerCase()=="input" && ele.type.toLowerCase()=="checkbox" && ele.checked)
m_count++;
if (ele.nodeName.toLowerCase()=="input" && ele.type.toLowerCase()=="checkbox" && !ele.checked)
m_count--;
if(m_count>5){
m_count--;
alert("最多不能超多5个主营项目！");
return false;
}
return true;
}
</script>
protected void chkAll_CheckedChanged(object sender, EventArgs e)
{
try
{
foreach (Control ctrl in Page.Form.Controls)
{
if (ctrl is System.Web.UI.WebControls.CheckBox)
{
((CheckBox)ctrl).Checked = chkAll.Checked;
}
}
}
catch (Exception ex)
{
throw ex;
}
}
var isChecked=true
function chALl()
{
o = document.getElementsByTagName("INPUT")
for(i=0;i<o.length;i++)
if(o[i].type=="checkbox") o[i].checked=isChecked
isChecked=!isChecked
}