[orf]

> Can you explain what Java offers with regard to reflection that JS doesn't?

Among hundreds of other things, getting the return type of a method and getting the input parameter names (+ types) in a way that doesn't revolve around literally parsing the functions toString() representation.

Oh, and typeof checking that isn't disgustingly broken.

[pitaj]

> getting the return type of a method and getting the input parameter names (+ types)

Type information literally doesn't exist at runtime, though. Isn't it kind of ridiculous to compare languages like that?

[orf]

When you're comparing the relative power of reflection within the language, absolutely not.

[untog]

But what would you use that information for, given that the language has no types? A JS function has no guarantees of what type a function returns anyway. It's like taking issue with the fact that a car doesn't come equipped with skis.

[stickfigure]

It's like taking issue with the fact that a car doesn't come equipped with skis.

To draw out that analogy... we live in Greenland. Cars with skis are surprisingly useful.

[lopatin]

> Type information literally doesn't exist at runtime, though.

Correct if I'm wrong, not all types get erased in Java. Doesn't type erasure only happen for generics? Say I have a non generic, plain Java class and want to inspect one of it's method's return types at runtime to see if it returns class A or class B. I can do that, right?

[stickfigure]

Yes, you are correct. There are also a number of circumstances in which you can get generic type info - it isn't erased, for example, if you create a concrete subclass of a generic type.

[pitaj]

I was talking about JavaScript. In JavaScript there are no typed functions or arguments, so that information doesn't exist period.

[lopatin]

Right, so I guess I'm not understanding your point about why comparing two languages like this is ridiculous. Java has a full blown runtime reflection system (it's "types exist at runtime"). JS doesn't. So Java wins in the reflection category.

[tracker1]

But in JS, reflection is pretty much not needed... I don't need to use reflection to see if an object has a quack method, or that I call it with the right types... I just call instance.quack() ... It's up to you as the developer to keep your interfaces and composition in line.

It's actually WAY easier than with C# or Java. Since the use-case of reflection itself is largely unnecessary.

[lopatin]

Calling a method and seeing what happens is not a substitute for reflection. You can do that in Java too btw.

[orangeeater]

> Among hundreds of other things, getting the return type of a method and getting the input parameter names (+ types) in a way that doesn't revolve around literally parsing the functions toString() representation.

Ah, that's quite cool.

[orf]

You can do almost anything with Java reflection, JS really pales in comparison.

Which in some ways is a good thing as you can do a lot more optimizations.

[spricket]

Typeof is a good one, but holy crap I had no idea return type and param support was that horrific