如何获得layer的id，急

Question

alert(document.all.Layer1.children[0].name)
alert(document.all.Layer1.childNodes[0].name)
alert(document.all.Layer1.nextSibling.name)

Answer 1

alert(document.all.Layer1.firstChild.name)
alert(document.all.Layer1.lastChild.name)

Answer 2

alert(document.all.Layer1.all[0].name)

Answer 3

<SCRIPT LANGUAGE="JavaScript">
<!--
   var i;
   for (i=1;i<=2;i++)
   {
    alert(document.all.Layer[i].all[0].name);
   }
//-->
</SCRIPT>
我希望时这样的效果，请问如何做到

Answer 4

alert(eval("document.all.Layer"+i+".all[0]").name);