typeof returning “unknown” in IE

Question

I have a window, where before being closed I refresh the underlying page.

if(opener && typeof(opener.Refresh) != \'undefined\')
{
    opener.Refresh(         


        

Answer 1

According to a duplicate question at Bytes, the typeof value unknown is added to JScript version 8, along with date.

A comment to a blog by Robert Nyman can also be explanatory:

Internet Explorer displays “unknown” when the object in question is on the other side of a COM+ bridge. You may not know this or realize this, but MS’s XMLHTTP object is part of a different COM+ object that implements IUnknown; when you call methods on it, you’re doing so over a COM bridge and not calling native JavaScript.

Basically that’s MS’s answer if you try to test or access something that’s not a true part of the JScript engine.

Answer 2

Try in operator. I had the same problem (with applet) and I solved it using in:

if("Refresh" in opener) {
    opener.Refresh();
}

Answer 3

The ECMAScript specification states that for host objects the return value of the typeof operator is:

Implementation-defined except may not be "undefined", "boolean", "number", or "string".

I believe the unknown value is only ever returned in Internet Explorer. Interestingly, MSDN does not mention it:

There are six possible values that typeof returns: "number," "string," "boolean," "object," "function," and "undefined."