UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36

Steps to reproduce the problem:
In the dev console, enter:

window["1"] = 1;

then

window["1"];

What is the expected behavior?
returns 1

What went wrong?
returns undefined

Did this work before? Yes Not sure, but worked in production Android System Webview until ~ one month ago

Does this work in other browsers? No
 Same behavior in Firefox

Chrome version: 60.0.3112.113  Channel: stable
OS Version: OS X 10.12.6
Flash Version: 

JTBC this is true for any key on the window that's just a string of a number.

our app (https://play.google.com/store/apps/details?id=com.makewonder.blockly&hl=en) relied on this working, and when it broke in the Android System Webview, it totally broke our app.

We're rolling out a fix but wanted to help resolve the underlying issue.

I don't have a strong view on whether you SHOULD be able to do window["1"] = 1, but the fact that you could before and can't now breaks existing apps that rely on it.
 

Deleted: window numerical key bug repro 264 bytes

window numerical key bug repro 264 bytes View Download