Unspecified error on Internet Explorer in an iframe with document.activeElement

[michaelwnelson]

This was brought up as an issue in VueJS as well.

In short, when inside an iframe in Internet Explorer, the document.activeElement check causes an unspecified error. Here is a screenshot of the error in the console:

It appears it has been resolved as an Internet Explorer bug recently However, it would appear this could also be addressed without waiting on an Internet Explorer update for users.

As benvirus' comment points out, it appears this can be address by changing the logic to check for document.activeElement to something along these lines:

try {
    return document.activeElement !== elm && elm.value !== checkVal
} catch (e) {
    return true;
}

[michaelwnelson]

After more research, it appears this can be mitigated by updating the check on window.document.activeElement.

I logged out window.document to find activeElement labeled as Permission denied.

I was curious how this resolved, so I logged out typeof window.document.activeElement and, surprisingly, it resolved to a type I did not know existed, unknown.

Here is my console.log() from my editor:

And here is the associated output in Internet Explorer:

Apparently, typeof value: unknown is recognized in IEs >=8 , see: http://stackoverflow.com/a/10982960/369687.

Therefore, I suggest updating the casted boolean check of canUseActiveElement from:

var canUseActiveElement = !!(typeof window !== 'undefined' && window.document && typeof window.document.activeElement);

To:

var canUseActiveElement = !!(typeof window !== 'undefined' && window.document && typeof window.document.activeElement !== 'unknown');