window.opera = null problem

[alisherdavronov]

I want to report a bug.

When there is a var named opera with value null in window before loading react then react app crashes.

Steps to reproduce:

1. Create a new app using create-react-app my-app
2. cd my-app && yarn start
3. Add one line (<script>window.opera=null</script>) just before closing body tag into file public/index.html
4. The app crashes here.

Couldn't reproduce on jsfiddle.net. I think because problem appears if we execute window.opera=null BEFORE loading react.

Expected behavior is to not crash.

React v16.2.0 and Google Chrome Version 63.0.3239.84 (Official Build) (64-bit).
Have no info about problematic behavior with previous versions of React.

[aweary]

Closed by #11854