怎么在javascript获得表单中单选按钮的值 _JavaScript

如何在javascript获得表单中单选按钮的值
如何在javascript获得表单中单选按钮的值并判断选择的是哪一个，请大家帮帮忙，谢谢

------解决方案--------------------
getElementById
getElementsByName
getElementsByTagName

判断 checked 属性
------解决方案--------------------

HTML code

<form onsubmit='return check()'>
<input type='checkbox' name='cb'/>
<input type='checkbox' name='cb'/>
<input type='checkbox' name='cb'/>
<input type='checkbox' name='cb'/>
<input type='checkbox' name='cb'/>
<input type='checkbox' name='cb'/>
<input type='checkbox' name='cb'/>
<input type='submit'/>
</form>
<script type='text/javascript'>
function check(o)
{
    var msg = "";
    var checkboxes = document.getElementsByName('cb');
    for(var i = 0 ; i < checkboxes.length ; i ++)
    {
        if(checkboxes[i].checked) msg +='第'+(i + 1) + "个被选中\n";
    }
    alert(msg)
}
</script>