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

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."