Comments on: Javascript puzzler: throw null

By: Adam

Adam — Mon, 15 Aug 2011 21:29:39 +0000

This particular case isn’t actually an example of static typing helping you.

Null is a perfectly valid value for something of type Exception or Throwable to have in java, so from a typing point of view there’s no reason that null exceptions couldn’t be thrown around. What stops this from happening in Java is simply the special case you linked to in the JLS (and the fact that underneath, it’s almost certainly doing something like expression.getClass().isAssignableFrom(Throwable.class) during the throw and expression.getClass() obviously throws a NullPointerException if expression is null).

It probably would make sense for Javascript to do something similar – throwing null is almost certainly a mistake, so when it happens automatically changing it to an Error(“null thrown”) might be better.

By: Nik

Nik — Wed, 30 May 2007 20:05:11 +0000

aarondr, you’re right that it’s not good practice to use the thrown object to identify the fact of the exception, but that’s much easier to say that after the event. The pain I experienced was due to someone else’s very poor code which threw null. But it was allowed to throw null due to Javascript’s typing being so loose its trousers are round its ankles.

Meanwhile, I’m not sure about that particular argument in favour of loose typing. I wouldn’t speak too ill of loose typing — it certainly has its place. But just because a language doesn’t trap compile-time errors it doesn’t follow that it therefore helps you trap runtime errors.

By: aarondr

aarondr — Wed, 30 May 2007 18:04:32 +0000

I know this is old, but I never really felt like using the object that is thrown is a good practice. Honestly, you know if the catch block executes that there was a problem, so why not just say,
problem_found = true;
One thing I have learned is to expect that ‘null’ may exist where I don’t expect, and if I don’t have control over the object, then I certainly don’t know what to expect out of it.

I prefer JavaScript over Java only to the fact that I have much more freedom of expression, and I am not having to keep strict types. Strict typing only offers compile time safety and error checking, runtime errors are much more dangerous anyways. I one respect, JavaScript lets you concentrate on removing the more important errors. This instance I blame the interpreter, not the language.

By: zproxy

zproxy — Wed, 11 Apr 2007 07:42:53 +0000

But you could compile statically typed language to javascript

visit http://jsc.sf.net