I've read different defenses for JavaScript for cases like this, which usually runs somewhere from you shouldn't be doing that anyway all the way up to if you just understood the language better you'd know why. While I agree with both of those points strongly as general principles, JavaScript also violates the principle of least surprise enough to make it concerning.
For what it's worth, I do like JavaScript. I really don't think that there is any perfect programming language.
JavaScript, like some other languages of the time, was designed with the Robustness Principle in mind. Arguably the wrong end of the Robustness Principle, but still.
That is, it was designed to accept anything that wasn't a syntax error (if not a few other things besides) and not generate run-time errors unless absolutely necessary. The thinking was that the last thing the user of something written in JavaScript wants is for their browser to crash or lock up because something divided by zero or couldn't find an object property.
Also it was originally written in about five minutes by one guy who hadn't had enough sleep. (I may have misremembered this part, but I get the feeling I'm not too far off.)
Sure. But in a sane language doing something totally nonsensical like that is an error, and in a statically typed language it’s a compiler error. It doesn’t just silently do weird shit.
Agreed! Unfortunately these maddening behaviors were kind of set in stone several decades ago, and it has been (correctly) decided "Don't break the web", these weird quirks are kept in modern interpreters/compilers.
It's actually quite interesting to read through the logic to follow when implementing an interpreter:
