<input type="checkbox" value="yes" id="hhh" onclick="xx()">
<script>
function xx()
{
if (document.getElementById("hhh").value=="yes")
{
document.getElementById("hhh").value="no"
return false;
}
if (document.getElementById("hhh").value=="no")
{
document.getElementById("hhh").value="yes"
return false;
}
}
</script>
<script>
function xx()
{
if (document.getElementById("hhh").value=="yes")
{
document.getElementById("hhh").value="no"
return false;
}
if (document.getElementById("hhh").value=="no")
{
document.getElementById("hhh").value="yes"
return false;
}
}
</script>
if(document.form1.tt.checked)
{
document.form1.tt.value="yes";
}
else{
document.form1.tt.value="no";
}
}
<form name="form1">
<input type="checkbox" value="yes" name="tt">
</form>