Tested in Safari 12 and Safari Technology Preview 12.1.
In the console I see:
[Error] SyntaxError: JSON Parse error: Unexpected identifier "undefined"
parse (linter.js:345:255)
(anonymous function) (linter.js:345:255)
s (linter.js:1:259)
e (linter.js:1:427)
Global Code (linter.js:1:444)
Tested in Safari 12 and Safari Technology Preview 12.1.
In the console I see: