How do I decode an encoded URL

How do I decode an encoded URL?
This question has been asked frequently (and variants of 'decode' keep showing up in this site's search logs). While the Server object provides a Server.URLEncode() method, they didn't bother providing a Server.URLDecode() or Server.URLUnEncode() method. I assume they didn't think it would ever be needed, but they were wrong... I've been in a few situations where this function would have been very handy. Here are both URLEncode and URLDecode functions (for completeness) in VBScript and JScript:

In VBScript:

<% 
    Function URLDecode(str) 
        str = Replace(str, "+", " ") 
        For i = 1 To Len(str) 
            sT = Mid(str, i, 1) 
            If sT = "%" Then 
                If i+2 < Len(str) Then 
                    sR = sR & _ 
                        Chr(CLng("&H" & Mid(str, i+1, 2))) 
                    i = i+2 
                End If 
            Else 
                sR = sR & sT 
            End If 
        Next 
        URLDecode = sR 
    End Function 
 
    Function URLEncode(str) 
        URLEncode = Server.URLEncode(str) 
    End Function 
 
    str1 = "http://www.foo.com/blah.asp?foo=1 & 2 &g=0" 
    str2 = URLEncode(str1) 
    str3 = URLDecode(str2) 
    Response.Write(str1 & "
" & str2 & "
" & str3) 
%> 

And here in JScript:

<script language=JScript runat=server> 
 
    function URLDecode(str) 
    { 
        return unescape(str); 
    } 
 
    function URLEncode(str) 
    { 
        str = escape(str); 
 
        // JScript doesn't think '/' needs to be escaped... 
        // I'm not sure it does either, but take it out to be 
        // consistent with VBScript's built-in URLEncode() 
 
        while (str.indexOf("/")!=-1) 
        { 
            str = str.replace("/","%2F"); 
        } 
        return str; 
    } 
 
    var str1 = "http://www.foo.com/blah.asp?foo=1 & 2 &g=0"; 
    var str2 = URLEncode(str1); 
    var str3 = URLDecode(str2); 
    Response.Write(str1 + "
" + str2 + "
" + str3) 
 
</script>