How can I quote iframe's javascript variable in parent's window

In A.html I open an iframe with B.html in it.

in B.html,I write js:

<script type="javascript">
    var b=0;

   function test(){
       alert(b);
       return b;
   }
</script>

so in A.html I want quote the variable b in B.html I write this:

<script type="javascript">
    var a;

    a=window.frames[0].b;
    alert(a);
</script>

but the resault is "undefined"; however,I quote the function test in A.html

<开发者_运维知识库;script type="javascript">
    var a;

    a=window.frames[0]. test();
    alert(a);
</script>

both the variable a and b could alert correctly

so why the second quote method could not work?

---

This works for me.

Which browser do you use? Are you sure that the document inside the frame is already loaded when you access the property?