请教js的for in的用法
<input   type= "checkbox "   name= "base "   id= "base1 "   value= "1 "   onClick= "javaScript:Checkbase(); "> 1
  <input   type= "checkbox "   name= "base "   id= "base2 "   value= "2 "   onClick= "javaScript:Checkbase(); "> 2
<script>
function   Checkbase()
{
var   boxs   =   document.getElementsByName( "base ");
for   (elm   in   boxs)
{
alert(boxs[elm].value);
}
}
</script>
为什么全都是undefine
而不是value呢

------解决方案--------------------
恩，調試下是很奇怪，爲何elm除了length之外，不是base1 base2，而都是base