A problem with the checkbox of Javasript

Problem

The JavaScript checkbox framework can be used as follows:

<form name= "List" method= "POST" >
<input Name=no type=checkbox>
<input Name=no type=checkbox>
<input Name=no type=checkbox>
</FORM>

In JS:
for (Var i=0;i<document.list.no.length;i++) {
if (document.list.no[i].checked) {
Allvalue +=document.list.no[i].value+ ",";
}
}

But when there is only one checkbox, the code above will run incorrectly. For example:
<form name= "List" method= "POST" >
<input Name=no type=checkbox>
</FORM>

Then Document.list.no.length document.list.no[0] will be undefined
Because it is now no longer an array. So just take the value. For example:
Document.list.no.value
Document.list.no.checked

Synthesis of the above situation, as long as in JS to be judged on the OK.
if (typeof (document.list.no) = = "undefined") cbvalue= "";
else if (typeof (document.list.no.length) = = "undefined") {
if (document.list.no.checked) Cbvalue=document.list.no.value;
}else{
for (Var i=0;i<document.list.no.length;i++) {
if (document.list.no[i].checked) {
Cbvalue +=document.list.no[i].value+ ",";
}
}
}