[WCJS] Uncaught error in IE11: SCRIPT5045 Assignment to read-only properties is not allowed in strict mode`

[LarsVonQualen]

Hi, so I have to support IE11, i know, not ideal.

When i include the webcomponents-bundle.js file, IE will throw this error SCRIPT5045: Assignment to read-only properties is not allowed in strict mode here: https://github.com/webcomponents/custom-elements/blob/master/src/CustomElementRegistry.js#L267

I'm not sure exactly why, or if this is even an issue, everything seems to actually work, it's just an annoyance, and i guess there's the risk of IE showing an unexpected error popup to the user.

It seems to me that the error should be handled gracefully thus not ending in console output.

Any thoughts? Or maybe even a way to get the error to go away? 😄