this should be decodable as JSON

Note that JSON is only a subset of JavaScript, you can see the grammar e.g. here - it doesn't even allow comments. That's why Perl's most common JSON modules, or browsers, won't handle it. Although the example code can be parsed with JavaScript's eval, of course that's a huge security hole because it allows for arbitrary code execution, which is one of the reasons why JSON was invented in the first place.