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Comment by kayoone | Hacker News Reader

"Just let that sink in for a moment — it's a mobile OS powered by JavaScript!"

Scary thought ;)

Web standards apps will always have to make bad compromises. We need browser byte code.

JavaScript is browser byte code. Just like Java byte code it's not that great for a lot of cases but, just like Java, eventually the JIT will get pretty decent.

Only by accident. It has terrible semantics for a target assembly.

I don't know. No matter how often I hear/see this, I just can't plausibly believe it. I think there are a lot of things missing to make JS a plausible Javacript.

For this reason I kinda want Dart to succeed. Why not make the browser truly polyglot if we are trying replace OS with browsers?

The JIT in the JVM is not for Java, but for Java bytecode. That, along with the easy integration into existing Java classes, is what makes the JVM such an attractive target for things like Scala, Jython, and Clojure.

Java bytecode is pretty close to Java "the language." You can try decompiling some Java classes and see how close to the original you end up getting.

Because of that it's also a pretty awful assembly target, something which is only now being addressed with things like invokedynamic, finally moving Java byte code beyond Java 'the language.'

What sort of compromises?

Having to target JavaScript. You then have issues with debugging, overly convoluted build processes etc.

It is. Sounds like a big waste of performance to me.

You'd be surprised at how well JavaScript performs when allowed.

The scary part of JavaScript is not performance, it is the hell of inconsistency.

'1' - 0 is 1. Guess what '1' + 0 is? Nope, it's '10'.

Crockford's JavaScript truth table is mind-bending. On top of that, semicolon insertion.

Type coercion and asi are probably the least troublesome odd parts of js I encounter day to day.

I find the weird scoping rules around 'this' and the verbosity of anonymous functions far worse. [1]

(Sincerely and non-rhetorically) Do you really find the former more annoying than the latter? I see a lot of people using those examples to call out JS inappropriateness for development, but it seems like they're focusing on the wrong things to me.

[1] I know they can be fixed by using a language that compiles down to JS. So can the parent's criticisms.

Not inconsistency to me. + is a string concatenation operator, - is not (maybe it could be) and '1' - 0 is just a fallback.

Not really scary day-to-day. If you want to do integer math, make sure you're dealing with integers.

It performs well, until the code is too complex for the JIT compiler to get type inference / speculative optimizations right. Then it suddenly performs very, very poor, because it falls back on dynamic (very slow compared to inline) dispatch and doubles instead of ints.

The language seems in need of refinement to get significant performance in match of JVM JIT, not to mention c.

Probably. I haven't witnessed that yet though.

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