Rails - May 2006 - Very strange javascript error

Some strange javascript errors happen in the situation:
Browser commits a xmlhttprequest to rails server,which will response 
some DOM data and javascript scriplets to add some operation to those 
DOM data.
All the following script are the responseText from webrick.
Error 1):
<script>
function Circle(x, y, r)
{
    this.x = x;
    this.y = y;
    this.r = r;
}
new Circle(0,0,0);
</script>
The above code will through "Circle undefined" error under both 
firefox1.5 and IE6
<script>
Circle=function(x, y, r)
{
    this.x = x;
    this.y = y;
    this.r = r;
}
new Circle(0,0,0);
</script>
This code will work normally,therefore,the following returned code will 
also through "xx undefined" error
<select  onchange="refresh();">......</select>
<script>
function refresh(){}//will cause "refresh undefined" error
/*
refresh=function(){}//will work normally
*/
</script>

What a strange!


Error 2):
Considering the follwing three scriptlets as a responseText to ajax 
request:
code one:
<script>
for (i=0;i<$(''divId'').options.length;i++){
  justforTest=0;
}
</script>

code two:
<script>
var len=$(''divId'').options.length
for (i=0;i<len;i++){
  justforTest=0;
}
</script>

code three:
<script>
len=$(''divId'').options.length
for (i=0;i<$(''divId'').options.length;i++){
  justforTest=0;
}
</script>

Of the three scriplets,only the last one will work normally,the former 
two will cause Firefox1.5 to collapse! (All three codes will be normal 
under IE)
Oooo~~~~~~

Anyone who can explain me for these errors?

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