共有四个复选框,当有两个选中,在点击第三个时,提示只能选两个。怎么实现?
如题
------解决方案-------------------- <head>  
      <title> Untitled Page </title>  
      <script type= "text/javascript ">  
         function cktest(ckvalue) 
         { 
             p=0; 
             var ck=document.getElementsByName( "test "); 
             for(i=0;i <ck.length;i++) 
             { 
                 if(ck[i].checked) p++; 
             } 
             if(p> =3) 
             { 
                 alert( "!!! "); 
                 ck[ckvalue-1].checked=false; 
             } 
         } 
      </script>  
  </head>  
  <body>  
      <form>  
      <input type= "checkbox " id= "test " value= "1 " onclick= "cktest(this.value) " />  
      <input type= "checkbox " id= "test " value= "2 " onclick= "cktest(this.value) " />  
      <input type= "checkbox " id= "test " value= "3 " onclick= "cktest(this.value) " />  
      <input type= "checkbox " id= "test " value= "4 " onclick= "cktest(this.value) " />  
      </form>  
  </body>  
  </html>      
 不好意思~   
 我实在想不出怎么取消特定的选择...所以就用了value 
 应该少通用性了...
------解决方案-------------------- <script language= "javascript ">  
 function chkbox(elm) 
 {var obj=document.getElementsByName( "cbox "); 
  var num=0; 
  for (i=0;i <obj.length ;i++ ) 
 	if (obj[i].checked ) 
      num+=1;	     
 	if (num> 2) 
 	{alert( "最多可以选择两个! "); 
 	 elm.status=false; 
 	} 
   } 
  </script>    
  <input type= "checkbox " name= "cbox " value=1 onclick= "chkbox(this); ">  
  <input type= "checkbox " name= "cbox " value=2 onclick= "chkbox(this); ">  
  <input type= "checkbox " name= "cbox " value=3 onclick= "chkbox(this); ">  
  <input type= "checkbox " name= "cbox " value=4 onclick= "chkbox(this); ">
------解决方案-------------------- <script language= "javascript ">  
 function chkbox(elm) 
 {var obj=document.getElementsByName( "cbox "); 
  var num=0; 
  for (var i=0;i <obj.length ;i++ ) 
 	if (obj[i].checked ) 
      num+=1;	     
 	if (num> 2) 
 	{alert( "最多可以选择两个! "); 
 	 elm.status=false; 
 	} 
   } 
  </script>    
  <input type= "checkbox " name= "cbox " value=1 onclick= "chkbox(this); ">  
  <input type= "checkbox " name= "cbox " value=2 onclick= "chkbox(this); ">  
  <input type= "checkbox " name= "cbox " value=3 onclick= "chkbox(this); ">  
  <input type= "checkbox " name= "cbox " value=4 onclick= "chkbox(this); ">  
------解决方案-------------------- <script language= "JavaScript " type= "text/javascript ">  
 var ichk=0; 
 function chksel(chk,sel){ 
 	if(ichk==2){ 
 		if(chk.checked){ 
 		alert( "最多只能选中两个! "); 
 		chk.checked=false; 
 		return null; 
 		} 
 	} 
 	ichk+=(chk.checked?1:-1); 
 	document.getElementById(sel).style.visibility=(chk.checked? "visible ": "hidden ");