UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36

Steps to reproduce the problem:
1. Open the attached file
2. Look at the console

What is the expected behavior?
Changing prototype of a NamedNodeMap instance should not affect values of own properties, so values before and after changing the prototype should be the same.

What went wrong?
After changing object's prototype to a Proxy instance, we loose access to some properties, which are object's own properties and therefore should not be affected by changing prototype.

The property "test" in this NamedNodeMap instance (attributes of a newly created div) is inaccessible. We can get it's value only via getOwnPropertyDescriptor.
Also, "in" operator returns false, while hasOwnProperty returns true, which is incorrect.

Did this work before? N/A 

Chrome version: 52.0.2743.82  Channel: stable
OS Version: 
Flash Version: 

Note that even if we change the prototype to null, it still works as it should, only changing prototype to a Proxy instance causes it to misbehave.

This works as expected in Firefox, and doesn't work in chromium 54
 

Deleted: test_proxy_namednodemap.html 909 bytes

test_proxy_namednodemap.html 909 bytes View Download