代码如下：
<SCRIPT LANGUAGE="JavaScript"><br />
<!--<br />
//checkbox元素的名字前缀，本例为sample1,sample2,sample3...<br />
var sCtrlPrefix = "sample";<br />
//checkbox元素数量，本例有18个；<br />
var iMaxCheckbox = 18;<br />
//设置最大允许选择的数量；<br />
var iMaxSelected = 5; <br />
function doCheck(ctrl) {<br />
var iNumChecked = 0;<br />
var thisCtrl;<br />
var i;<br />
//初始化<br />
i = 1;<br />
//循环直到选中了最多的checkbox;<br />
while ((i <= iMaxCheckbox) && (iNumChecked <= iMaxSelected)) {<br />
thisCtrl = eval("ctrl.form." + sCtrlPrefix + i);<br />
if ((thisCtrl != ctrl) && (thisCtrl.checked)) {<br />
iNumChecked++;<br />
}<br />
i++;<br />
}<br />
// 检查是否达到了最大选择数量；<br />
if (iNumChecked == iMaxSelected) {<br />
// 如果是则uncheck刚选择的元素；<br />
ctrl.checked = false;<br />
}<br />
}<br />
// --><br />
</SCRIPT><br />
<br />
<form name="form" method="post"><br />
<table align="center" border="1" cellpadding="5" cellspacing="0"><br />
<tr> <br />
<td> <br />
<input type="CHECKBOX" name="sample1" onClick="doCheck(this)"><br />
A</td><br />
<td> <br />
<input type="CHECKBOX" name="sample2" onClick="doCheck(this)"><br />
B</td><br />
<td> <br />
<input type="CHECKBOX" name="sample3" onClick="doCheck(this)"><br />
C</td><br />
</tr><br />
<tr> <br />
<td> <br />
<input type="CHECKBOX" name="sample4" onClick="doCheck(this)"><br />
D</td><br />
<td> <br />
<input type="CHECKBOX" name="sample5" onClick="doCheck(this)"><br />
E</td><br />
<td> <br />
<input type="CHECKBOX" name="sample6" onClick="doCheck(this)"><br />
F</td><br />
</tr><br />
<tr> <br />
<td> <br />
<input type="CHECKBOX" name="sample7" onClick="doCheck(this)"><br />
G</td><br />
<td> <br />
<input type="CHECKBOX" name="sample8" onClick="doCheck(this)"><br />
H</td><br />
<td> <br />
<input type="CHECKBOX" name="sample9" onClick="doCheck(this)"><br />
I</td><br />
</tr><br />
<tr> <br />
<td> <br />
<input type="CHECKBOX" name="sample10" onClick="doCheck(this)"><br />
J</td><br />
<td> <br />
<input type="CHECKBOX" name="sample11" onClick="doCheck(this)"><br />
K</td><br />
<td> <br />
<input type="CHECKBOX" name="sample12" onClick="doCheck(this)"><br />
L</td><br />
</tr><br />
<tr> <br />
<td> <br />
<input type="CHECKBOX" name="sample13" onClick="doCheck(this)"><br />
M</td><br />
<td> <br />
<input type="CHECKBOX" name="sample14" onClick="doCheck(this)"><br />
N</td><br />
<td> <br />
<input type="CHECKBOX" name="sample15" onClick="doCheck(this)"><br />
O</td><br />
</tr><br />
<tr> <br />
<td> <br />
<input type="CHECKBOX" name="sample16" onClick="doCheck(this)"><br />
P</td><br />
<td> <br />
<input type="CHECKBOX" name="sample17" onClick="doCheck(this)"><br />
Q</td><br />
<td> <br />
<input type="CHECKBOX" name="sample18" onClick="doCheck(this)"><br />
R</td><br />
</tr><br />
</table><br />
</form>
[Ctrl+A 全选 提示:你可先修改部分代码,再点运行代码]
