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

My feeling is that reflection is almost moot in JS since you can inspect/mutate objects at runtime however you like. But maybe I'm missing the point of reflection.

There is a Reflect object with a bunch of static methods on it in ES6. It mostly just replicates functonality that already exists in the language, and my suspicion is that it's mainly there so it can be extended at a later date without breaking backwards compatiblity.

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.

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

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

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?

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

Ah, that's quite cool.

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

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.

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

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.

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

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).

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.

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.

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
        }
    }

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.

No, its Java EE, which like I said, has an entire library devoted to safe marshalling[1]. Marshmallow does the same thing for you in python. Java EE including a marshalling library has nothing to do with static typing.

This is python + flask + marshmallow (2 very common web libraries)+ a 2 line helper function:

    @dataclass
    class Thing():
        text: str
        when: datetime.datetime

    @app.route('/thing', methods=['POST'])
    def handle():
        thing = unmarshall(Thing, request.form)
        # blah

    from thingproto import Thing, ThingService, ThingResponse

    class ThingServiceHandler(ThingService):
        def HandleThing(request: Thing, response: ThingResponse):
            # blah

[1]: https://dennis-xlc.gitbooks.io/restful-java-with-jax-rs-2-0-...

Dragging protobufs into this is weird too; you've ignored the IDL and build infrastructure required to set that up, and in any case that's specific to when you're working with protobuf APIs.

I'll go back to my earlier point, which I think you've illustrated fairly well, which is that well-written Java code tends to be more concise and less verbose than Python (and friends). Our two examples are nearly identical in terms of meaningful lines of code, but in the Python example you have to ask for marshaling.

I'll also point out that flask (which I use myself for python webapps) handlers are forced to interact with flask-specific objects and therefore are obnoxious to test; the JAX-RS example is pure program logic and can be tested as vanilla Java code. This is one of the big advantages of moving marshaling "out" of your program code.

That's only an API wart. It'd be possible to elide that pretty easily if someone wanted to write a library to do that.

I could write a library function or flask extension or whatnot that resulted in

    @app.myroute('thing', method=['POST')
    def handle(thing: Thing):
        # work with thing

>I'll also point out that flask (which I use myself for python webapps) handlers are forced to interact with flask-specific objects and therefore are obnoxious to test

Huh? Here's an example of a test from the flask docs[0] that makes a request and checks the result.

    def test_empty_db(client):
        rv = client.get('/')
        assert b'No entries here so far' in rv.data

1. There should be minimal logic in the handler. You should defer most logic to a library function, you can also not use the decorator form and instead declare `app.route('/path')(function)` and just test function itself.

2. Even testing the handlers and doing end to end stuff with a running server isn't that hard. I'm not sure what you're experience was, but my guess is you weren't leveraging existing libraries.

>This is one of the big advantages of moving marshaling "out" of your program code.

Here's the implementation of that:

    def myroute(self, *args, **kwargs):
        def wrapper(f):
            @self.route(*args, **kwargs) 
            def new_route(*args):
                arg, schema  = f.__annotations__.items()
                parsed = schema.load(request.form)
                return f(arg=parsed)
            return new_route
         return wrapper

Flask however is relatively generic, it can handle things that your java examples can't, like an endpoint where you don't know the schema, which might happen if you're doing something like hosting a user-provided function or something of that nature (I implemented an AWS-lambda style thing in a hackathon with that). Something like

    @route('/user_endpoint')
    def handle():
        return convert_to_html_response(user_function(**request.form))

Flask lets you do that. If you want to restrict yourself to schematized requests, you have more information and can make more assumptions, but flask isn't a REST framework, its a generic web framework. If you want to restrict yourself to something with known schemas, you can do that pretty concisely[1], even when dealing with relatively complex marshalling (and you can do it outside of your logical code under test via decorators).

[0]: http://flask.pocoo.org/docs/1.0/testing/

[1]: https://flask-restful.readthedocs.io/en/0.3.6/fields.html

    @POST
    public void doSomething(final Map<String, Object> thing) { ... }

Also you kinda missed my point about unit tests. Your test requires specialized flask-oriented objects (client, rv). Tests of the Java doSomething() can be written entirely without knowledge of the container; doSomething() is pure program logic. And the methods support refactoring.

you picked something that java has libraries specifically catered toward

I picked a basic REST service. I'd call that a pretty common use case.

There should be minimal logic in the handler. You should defer most logic to a library function

Again illustrating my point that well-written Java is more concise. You don't need to do this! The Java "handlers" I've shown are pure logic. There is no point in wrapping it with another layer.

Sure, you probably could build a webapp framework that makes Python a lot more like Java. But so far nobody's done that. So Python programmers write wordy verbose flask apps with tons of validation and marshaling logic. It's tragic.

More verbose than the Python.

>Sure, you probably could build a webapp framework that makes Python a lot more like Java

Not could, did. Literally just did, in 10 lines of code. Or there's flask-rest, which I linked.

>Again illustrating my point that well-written Java is more concise. You don't need to do this! The Java "handlers" I've shown are pure logic.

And flask-rest does that! If you're writing a restful service the more concise, better specialized tooling is readily available.

Now write the unmarshalling code and tell me Java is still more concise.

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

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.

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.

1: http://typeorm.io/

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>

    router.get('/users/:id', (id: UUID) => ...)
    router.get('/products/:id', (id: Int) => ...)

    router.get('/users/:id'. skipNonUuid(id => ...))

You can do function composition that is nearly as simple and far more flexible in general with JS

There's no way to hook into the loading of modules in a standard way - you have to know how the modules are compiled and required.

One thing comes to mind, how to twinkle stuff inside closures?

Though Java was 'designed', it was not 'designed' to be an http/web server.

JS, particularly Node.js has really adapted itself to that well.

And one small but massive difference: JSON is how data is passed and it fits seamlessly into Javascript, and doing JSON in Java is an ugly, ugly thing.

As soon as you compare not JS/Java, but Java/Tomcat vs. JS/NodeJS - then you get a different comparison.

I quite like using Typescript on Node.js over Java - development speed is faster, and this is a really important thing.

It is only a matter of browsers getting native support for gRPC.

With gPRC there's still a lot of binding code, and you need to map all of that in Java, but you do get some validation etc. out of it. It does make the 'data transfer' comparison a little less harsh.

[1] https://github.com/grpc/grpc-web

It's a very specific technology, and as long as it can be implemented fairly efficiently 'up the stack' in JS, then it mostly belongs there. Aside from HTTP2 (which is a roadblock now, but not soon) it'll be fine in JS.

https://en.wikipedia.org/wiki/Billion_laughs_attack

It got me thinking about it. JSON is annoyingly simple at times, yes. But that also protects it from some pretty gnarly stuff seen in XML and YAML. I suspect it's a considerable contributor as to why it's the choice transport format.

I wouldn't toss it in with XML just yet.

Why do you think so? Jackson and Gson work very well. Serialising and deserialising from/to POJO/JSON is trivial with them.

In Java, you have to abstract the document and write a lot of code to access, add, remove things etc. - or - because there is no such thing as an untyped POJO in java, you have to set up a ton of things if you want to use real objects.

You could also use a POJO for the fields you know and put a map inside for the fields you don't know.

If that's not enough you can use JsonNode, or ObjectNode where you can freely add and remove json values.

But yeah json is much nicer in JS generally

At least, that is how I find it, my productivity shoots up when I don't have to be moving between two imperative languages that most likely share a lot of their syntactical DNA with C but each have their own fun little differences.

I guess you could hire less proficient engineers which is a sell for startups, but I don't think it's worth the downsides of the current js ecosystem

I have mixed feelings about this. I don't feel comfortable with assuming that just because I use the same library in backend and frontend, I don't have to ensure consistency and behaviour. But then again, I've used this approach in one ClojureScript project (ClojureScript can transpile a lot of Clojure libraries to JS), and it is convenient.

And don't associate less proficient engineers with Javascript dude !

And that is only when not using JSF, Spring, Forms, MVC, Liferay, Sitecore, which generate the JavaScript validators automatically from type annotations anyway.

For my projects, the Web layer is only the View part of MVC.

Aside from form validation I find I might have a number of utility functions that are used on both layers.

I find there are a few other edge cases, but those are the most common situations where reuse is nice (on the other hand what I often do for personal projects is just build the server side and client side code from a gulp pipeline and not worry about needing 'isomorphic' code reuse, but often teams on paid for projects find this approach confusing)

[1] Whoever came up with isomorphic really liked their fancy math terms. Personally I'd have chosen automorphic, as it's all contained inside JS.

There is something precious to being able to do more with substantially less code, which is why I avoid OOP all together. You can't do that in Java.

Oh god...

Yeah, no. None of this stuff is a substitute for actual code quality. Give me a good engineer that refuses to write tests over a mediocre one that does TDD any day.

Linters: ErrorProne Checkstyle PMD SpotBugs Nullaway

All with highly customized settings

All warnings enabled on javac

Google-java-format to autoformat everything on build.

For runtime analysis: LeakCanary to find memory leaks

Hibernate with interceptors to find long queries

Rest framework or gRPC with interceptors for long calls

Proxied JDBC connector to find long or N+1 queries

Opentracing/Zipkin integration to make debugging crazy stuff easier

NewRelic for projects where the $ makes sense

And I'm always on the lookout for more of these tools. In the long-run they save enormous amounts of time by preventing buggy code and keeping most shitty hacks out of the codebase.

Unlike tests, they don't break constantly and add more maintenance burden to the codebase. And it's less work, one time setup vs ~50% codebase bloat to add tests.

I see project leads call for more tests all the time to "fix" an unreliable codebase where there's zero linting. It won't save you from everything but I swear it's like 95% bug reduction. You should have most/all of these tools in place before you consider writing the first tests

No, you can't.

In fact, I can't even begin to see how "apply this specific standard to the code" (linting) is even remotely related to "know everything about this particular domain so you don't make any mistakes in creating an application for it" or "know everything about this particular system so that a given difference in configuration screws up your application at run time".

You seem to be primarily a java developer so I understand why you prefer avoiding tests (among the many things that Java makes absurdly difficult, writing tests is one of them) but you should still write tests .

Look at any serious open source project, most of them have hundreds, thousands of tests. It's almost presumptuous to think that one knows more than the community.

> I swear it's like 95% bug reduction.

The only situation where linting really causes that much of an impact, that I've seen, is in an application where a huge portion of the code was just connecting or boilerplate that should've been brought from third party libraries anyway, and was written only because of the NIH syndrome.

Mind you, having code style is necessary so that any given developer can quickly get up to speed and more easily review other developer's code, but it doesn't (nor it shouldn't) tell you whether whatever you wrote actually works.

Assuming otherwise is like pretending that a movie featuring state of the art special effects, cinematography, etc, isn't still Transformers or similar garbage.

For the average crud app, if you're wrong about the requirements the tests will be wrong anyways. It sounds like you're talking more about TDD which IMO is a cargo cult. And I'm hardly the only one with that opinion. Integration tests are important but that's more about running data through the code all at once than testing each function in isolation.

Also, many open source projects get along with hardly any tests. The Linux kernel is probably the best example, but there's tons of popular projects without good or any tests. Check NPM popular repositories, I'll bet you more than half of the top 500 are under 10% code coverage. Tons of huge apps are doing fine without tests, and many I've worked on with tests are still horrible.

I haven't really noticed any contribution from having lots of tests. IMO what's far more important is linting and maintaining code standards. It's hard to write a function that's horrible to debug when the linter limits you to 300 lines. Or a class that's totally incomprehensibly long when the linter limits you to 1000. All of my debugging nightmare projects have been due to lack of sound OOP principles, huge files of spaghetti. Good linting prevents that from happening.

Besides Java my other big language is TypeScript. Using Mockito in java isn't that bad, and JUnit5 or TestNg are decent. Certainly easier than getting tests working in the garbage fire that is Angular6 + Jasmine + Karma.

You might be surprised how much bad logic static analyzers can catch though.

But TDD is about neither, it's about test-first approach at the unit test level, which is arguably less useful and leads to design by random walk.

There's always a trade off.

CRUD apps generally go into production, unless something goes horribly wrong.

Compared to when I'd have to use ActionScript, JavaScript, VBScript, VB6, T-SQL daily... that was sometimes painful... then adding C# and VB.Net to the mix was ugly having to switch from one area of code to another.

Just choose the best programming language, and everyone can learn it; and they'll be happy and grateful in the long run that they chose to learn this new language, rather than use whatever they were familiar with.

Moreover, Java is such a simple and an easy language to pick up. If the cruft is too much to deal with, go with Kotlin. An experienced developer could learn either language (Java or Kotlin) easily over a single weekend.

Also, it's easy to learn a language's syntax over a weekend, but it generally takes a lot longer to start being productive and writing idiomatic code in a new language, especially if you're also learning a new platform. That's time that you or your team may not have.

Since ES6 it's even better.

Python not as scalable, Rails is stagnating, the ecosystem doesn't evolve anymore/dying, doesn't play well with SPAs, C# weak to none ecosystem outside of Windows and devs earn a fraction, Java verbose and dev productivity subpar (there was a reason people came up with Scala), Java devs also suffer lower salaries

Not scalable in what way? Every aspect of scalable that I can think of is in no way limited by choosing python as your language.

Mayne that is your problem. Try new stuff. V8 is still one of the fastest and most optimized VMs.

If you reach out to the Java ecosystem you can find libraries, frameworks, and language extensions that make it relatively easy to code in. For example, with Lombok you don't have to write any getters and setters, or catch checked exceptions. Java 11 also makes good improvements to lamdas making method chaining a lot nicer. The Java I write at work is barely more verbose than the TypeScript, maybe 15% more code to do the same thing.

Java devs also get paid really well honestly, pretty sure it's better than the pay for JS and Python actually.

Huh? Rails ships with built-in, no-config webpack support (https://github.com/rails/webpacker#installation) as well as install tasks for the most-popular front-end solutions (https://github.com/rails/webpacker#integrations)