Symptoms

After the just-in-time (JIT) compilation of certain JavaScript functions, Internet Explorer 11 may return an incorrect JavaScript typeof result for host and DOM objects in non-edge document modes.

Resolution

Update information

To resolve this problem, install the most recent cumulative security update for Internet Explorer. To do this, go to Microsoft Update. Additionally, see the technical information about the most recent cumulative security update for Internet Explorer.

Note This update was first included in March cumulative security update for Internet Explorer (MS15-018).

More information

This issue occurs because of a timing issue with Internet Explorer when it requests the embedded resources. The working status is listed as follows:

"if (typeof x == …)" // works fine
"y = (typeof x == …)" // does not work fine. Work around: "y = (typeof x == … || false)"
"return (typeof x == …)" // does not work fine. Work around: "return (typeof x == … || false)"

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

References

See the terminology that Microsoft uses to describe software updates.

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