UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36

Steps to reproduce the problem:
1. Open dev console in browser
2. Type a
3. Throws ReferenceError: a is not defined
4. Type let a = JSON.parse("{")
5. Throws SyntaxError: Unexpected end of JSON input
6. Type a
7. Throws ReferenceError: a is not defined
8. Type let a = 5;
9: Throws SyntaxError: Identifier 'a' has already been declared

What is the expected behavior?

What went wrong?
Won't let me redeclare variable a when it fails defining, but still says it's not defined.

Did this work before? N/A 

Chrome version: 67.0.3396.99  Channel: n/a
OS Version: OS X 10.12.6
Flash Version: