xml数据筛选，请帮忙！

Question

<?xml version="1.0" encoding="utf-8"?>
<TreeNodes>
  <Treenode CategoryID="1" CategoryName="基本设置" FatherID="0" IsChild="">
  </Treenode>
  <Treenode CategoryID="2" CategoryName="个人设置" FatherID="1">
  </Treenode>
  <Treenode CategoryID="3" CategoryName="部门代码设置" FatherID="1">
  </Treenode>
  <Treenode CategoryID="4" CategoryName="储位设置" FatherID="1">
  </Treenode>
  <Treenode CategoryID="5" CategoryName="请购作业" FatherID="5">
  </Treenode>
  <Treenode CategoryID="6" CategoryName="请购申请" FatherID="5">
  </Treenode>
  <Treenode CategoryID="7" CategoryName="请购查询" FatherID="5">
  </Treenode>
</TreeNodes>如上xml数据，怎样用javascript根据FatherID和CategoryID选数据?

Answer 1

var v = getElementsByTagName("Treenode");
if(v.CategoryID=="5")
{}

Answer 2

var v = getElementsByTagName("Treenode");
怎样得到多少条记录？可以给个例子吗？