Seems like "this is why Javascript sucks!" is a common reaction here, which I find strange on a "hacker" community. It's a fun little brainteaser, not production code. Use your head a little?
About the only problem I can think of here is that it makes
it harder to filter/sanitize for XSS. But I don't think the problem here is Javascript. Look at SQL injection - trying to escape user input is just an endless game of whack-a-mole. The proper way to deal with it is parameterized queries. HTML doesn't have anything similar AFAIK.
I don't think this particular nuance of the languadge has much effect on productionilized code, this is a very specific observation built by someone who understands the nuances of JavaScript deeply. As such it would take the opposite of ignorance to get something like this into production, you would have to know the nuances of the language pretty deeply to get code like this into a system.
There are some gotchas is JavaScript like the (== for 0, null, ""), the floating scope of (this) and a few others but for the major use cases of JavaScript people only need to be aware of a handful of languadge nuances to not hang themselves. It has some quarks no doubt about it, but for the most part they are easily avoided or you have to know about them to be doing what you are doing in the first place.
