[spricket]

Java uses reflection and annotations to support all kinds of language extensions. Js has a lot of nasty issues with the "prototype chain" and annotation support is still experimental. For example, in java, scanning your classes and their annotations to generate code for them at compile time is a standardized feature.

Maybe I'm just complaining that JS is too dynamic, but being able to generate code at compile time with reflection and know it will generally work (type checked) is nice.

[kangoo1707]

Do you have any concrete example for "For example, in java, scanning your classes and their annotations to generate code for them at compile time is a standardized feature"?

Tip: in JS, I don't want OOP class. If you really want class, could you show me the intention behind it?

[gwright]

In general this what java annotation processors are all about. As a specific example, Dagger, a compile time, type safe dependency injection framework. https://google.github.io/dagger/

[spricket]

Java only works in classes :) . They're actually the compilation unit as well so no way around it. (Files are compiled a .class file at a time from single source files)

Adding another example, JPA MetaModel generator that allows you to make strongly typed calls in ORM.

Basically, it let's you generate code at compile time that's seamlessly integrated into the existing code. So it's generated code that still gives you IDE autocomplete support etc.

[stickfigure]

Every popular ORM uses reflection to determine how to map fields to columns. For example, what type of date or money object to use.

I automagically map some postgres JSONB columns to a parsed object form. Looks just like a regular typed nested object.

[hajile]

That's a solution looking for a problem in JS. You're thinking in types instead of in terms of a dynamic language.

You basically HAVE to do this in Java otherwise your program won't work. In JS, you can look everything over at runtime and dispatch from there (made much easier because first-class functions and closures are a thing).

[stickfigure]

you can look everything over at runtime

Correct, that's what you have to do in dynamic languages - look at what came in from the database and manually validate+convert it into the format you actually want. Also with pretty much every other form of input (JSON bodies, form posts, queue messages, etc). It's a lot of tedium.

When working with node/python/ruby, I often find myself wishing I could just declare a type and be assured that "the system" will get it right instead of me having to code it out myself. You know, like Java.

Well-written Java programs are generally more concise and less verbose than well-written JS/Python/Ruby programs. Which is to say, when programmers actually validate input instead of (ahem node) crashing the process and dropping all inflight connections when someone submits a json body missing an expected field.

BTW absolutely nothing prevents you from building Java apps by declaring everything as Map<String, Object>. Nobody does that because it's a horrible way to program.

[joshuamorton]

> Well-written Java programs are generally more concise and less verbose than well-written JS/Python/Ruby programs.

This isn't at all true. I can say this from experience using statically typed Python extensively, in an average code base, 80% of your functions, if not more, are already statically correct in Python, one just need add an annotation. Then you're just as "well written" as the Java.

With or without the annotations, the code is still just as "correct".

> BTW absolutely nothing prevents you from building Java apps by declaring everything as Map<String, Object>. Nobody does that because it's a horrible way to program

Yes, but only because you'd need to explicitly cast things everywhere and write out declarations everywhere. If you could always elide casts and type defs, it becomes a lot less horrible.

> Correct, that's what you have to do in dynamic languages - look at what came in from the database and manually validate+convert it into the format you actually want.

You still have to do this in static languages. Maybe a library does it for you, and it gives your an error or something you know is a DbRecordFieldStream or whatever, but dynamic languages can do the same thing. Orms validate input in dynamic languages too. Rails and Django can validate request formats. Protobufs work in every language.

[stickfigure]

> This isn't at all true.

Well I guess we'll just have to disagree there. I spend a lot of time writing code in all of these languages. By the time you've bulletproofed your dynamic code, you've got more code than if you'd just declared a simple static Java type.

I can define this...

    @Data
    public class Thing {
        final String text;
        final Instant when;
    }

    @Path("/thing")
    public class ThingResource {
        @POST
        public void doSomething(final Thing thing) {
            // ...blah
        }
    }

...and stop worrying in my implementation about what was actually passed in, or how a JSON string date got turned into a real date representation. This is mostly-vanilla Java.

Sure you can, with enough extra code and clever libraries, hack together a crude typing system into dynamic languages to automate much of the conversion. At the end of the day you're still declaring types, and it doesn't end up being as elegant as having the type system built into the language.

[tracker1]

Why do I need to manually convert anything? Even then...

    var results = (await sql.query`
      ...
    `).recordsets[0].map(rowToObject);

It's really easy... no need for complicated ORM/ODM tooling at all.

As far as the size... create a docker container from node:10-alpine to run a given node application, and create a similar container with any application running full Java. And compare the final size.

[stickfigure]

Did a date column get mapped to Date, moment, date-fns, luxon, or any of the dozen other choices that your shop might standardize on?

I've never heard anyone server-side care about the size of a deployable. It's the size of the codebase that's an issue. Tedious conversion code does not work in javascript's favor.

[tmerse]

You should have a look at typeorm [1]. Typescript ORM with decorator support.

1: http://typeorm.io/

[stickfigure]

That's cool, and will keep it in mind for the next time I work on a node project.

Looks like it works by having the typescript compiler generate experimental annotations in the output javascript, and reading it using a polyfill for the proposed ES7 reflection api. On one hand, yeay looks like proper runtime reflection is coming! On the other hand, it doesn't sound fully baked yet... <insert here a general grumble about how everything in the JS ecosystem is in this state>

[gwright]

Retrofit is another example: https://square.github.io/retrofit/

[buerkle]

http://immutables.github.io/ makes great use of this feature in Java