Writing code for JS and Java - javascript

I'm trying to write a module of code which can be used with Javascript for the client side browser and Kotlin for a Java desktop application and Android app.
The main logic manipulates a bitmap/png file.
Is there a way which I can write an interface to be used and have different implementations of the interface for JS and Kotlin?
For example, write a wrapper class for an image (load from image, set pixels, get pixels) in Java (using BufferedImage) and JS (using Canvas)?
I'm new here so if anything doesn't make sense or needs more clarification, please let me know!

Yes, it's certainly possible to do that. This answer is a generic Java and JavaScript answer; there may also be a Kotlin-specific approach, see the link in zsmb13's comment. But the generic Java and JavaScript approach would be:
Write your interface around BufferedImage in Java
Write your interface around canvas in JavaScript
Write your manipulation code using that interface in JavaScript
On the browser, your manipulation code would run directly on the browser's JavaScript engine
In the Java app, you'd run your JavaScript code using javax.script to run it in Nashorn (or Rhino on older Java environments).
Whether it's the best solution to your problem is something only you can decide, but yes, you can do it.

Related

Javascript frameworks just "markup" for javascript?

I am a little curious about how javascript frameworks work. Web development isn't really my area of expertise (I'm more of a c/c++ guy), but do javascript frameworks get translated into vanilla javascript?
Upon inspection of website source, it seems like it is mostly just standard javascript. Do these javascript engines just translate code into javascript on the server side?
Yes, most of JavaScript Frameworks translates the code you write to vanilla JavaScript, however, this does not happen on the Server Side, that would be really slow (Server side code is used to check databases, serve files, authenticate, etc.). This process of translation is done in compilation time (Although it is translation). (Just like when you compile c++ code into binary).
When it's source code to source code like JavaScript and React (JSX) to Vanilla JavaScript (JS), it's translation. When it's source code to binary like C++ source code to an executable (.exe) is compilation.
After you're done writting your JavaScript code with frameworks, you most translate it to Vanilla JavaScript (if you also used other uncommon languages to write styles, you must translate them too, like SASS instead of CSS). It is also common to minify it, so it can load faster.
All this is mainly done by tools like webpack.
When your site is up and running, we can say that is run time.
Looking at the fact that they were written in js they would be resolved to js before running and as Robin said they are executed on client side except Node which is a runtime environment and not a framework

Create WebAssembly using c#

I went through below article
https://medium.freecodecamp.org/get-started-with-webassembly-using-only-14-lines-of-javascript-b37b6aaca1e4
and very impressed that we can use c++ code in javascript using web assembly.
Do we have any option to create such web assembly using c# where we can create web assembly and use in javascript like angular or react.
went through
https://learn.microsoft.com/en-us/aspnet/core/client-side/spa/blazor/get-started?view=aspnetcore-3.0&tabs=visual-studio
But that does not look like creating an assembly that can be used in a separate angular only project with by importing
Thanks
From msdn:
JavaScript interop
For apps that require third-party JavaScript libraries and browser APIs, Blazor interoperates with JavaScript. Components are capable of using any library or API that JavaScript is able to use. C# code can call into JavaScript code, and JavaScript code can call into C# code. For more information, see JavaScript interop.
[https://learn.microsoft.com/en-us/aspnet/core/client-side/spa/blazor/?view=aspnetcore-3.0][1]
Ithink looking to Blazor source code can help you to.
I think what you're looking for isn't Blazor, because it's a complete UI framework for ASP.NET client/server stuff using SignalR, that uses WASM at the client side. Maybe too much for your purposes, even if you're able to use any JavaScript framework together with Blazor, too.
But you're looking for a simple way to create just a WASM that exports methods to JavaScript that you can write using C#, right? Well, then I suggest you to have a look here:
https://itnext.io/run-c-natively-in-the-browser-through-the-web-assembly-via-mono-wasm-60f3d55dd05a
It seems the Mono way is working as you'd expect: You write methods in C#, compile a WASM and then you're ready to load and call them from any JavaScript client app, and you don't have to deal with ASP.NET stuff at all.
Compared to a WASM that has been created using lower level C++, you'll have a big bunch of DLLs for the Mono runtime, that need to be loaded to the client browser (!). That's a huge overhead, if you plan only a small feature set to be exported by the WASM. The best argument for creating WASM using Mono for me is, that I can use my existing codebase with all the algorithms and business logic for a really complex app, so I don't have to write and maintenance the same code twice in different languages.

How to execute Javascript code in a WinRT C# application?

I am writing a WinRT application in C#.
I would like to execute some Javascript code. An entire WebView is not needed in my case, I just need to interface with a Javascript virtual machine. The C# code would call Javascript functions and would export some objects to the Javascript side.
I know there is JsRT, the C API of Chakra, the jsvm used by Internet Explorer. But JsRT, as far as I know, is not available to WinRT. Other virtual machines are not allowed under WinRT.
So, the question is: is it even possible to call Javascript code from C# code? If not, waiting for the release of JsRT for WinRT is the only option?
It's possible to call JavaScript from C# but not without a WebView control.

Expose javascript logic to a web service

How to expose a javascript logic which is currently there in a legacy system as a webservice?
Only way to do this is convert javascipt code to a another language right? Im finiding a way of expose the javascript code directly as a webservice because it has thousand of codes. So convert those to a java or other language is a huge effort.
You need to put some sort of wrapper around the JS that can take input and output via HTTP and call the appropriate JS functions.
You could write the entire thing using node.js or you could use another language which has an interface to a JS engine such as Perl or Java.

Is there a Java byte code reader implemented in javascript?

I know there are lots of libraries that read byte codes that are written in Java. Does someone know of a byte code library that is implemented in Javascript?
Since javascript is typically run inside a browser, it generally cannot read the actual bytes out of files, which makes it less-than-ideal for reading java bytes. If you somehow got the byte codes encoded in a form that the javascript could read, what would you expect the library to do with it? Can you provide more details about what you're trying to do?
If you're looking to be able to write code in Java, and have it run inside a browser, take a look at GWT. It uses Java to recompile your byte-code into optimized javascript.
Edit
Based on your added comment, that you are hoping to "find out the classes and methods used in a jar file on my local disk":
Since javascript is unable to access files on a local disk (at least, without using ActiveX), the technology simply won't allow for this sort of thing. Is there a reason you wanted to use javascript for this, rather than java?
And please accept my apologies if it sounded like I was questioning your motives. I really just wanted to get enough information to be able to adequately answer your question.
Update:
It looks like the Japanese project I tried to link to below is long gone.
In any case, time has passed and now there are a couple of hits for "jvm in javascript" on Google. Namely:
Doppio
BicaVM
Look what I found:
http://ejohn.org/blog/running-java-in-javascript/
Does this help?
Edit: unfortunately it looks like the original project's site is dead.
You could try through the Web Archive, here (in Japanese, tried to Google translate it, but I guess it was too much indirection :))
For goodness sake, if you follow that link, run your download through an anti-virus.
I don't know if it's trustworhty.
There are compilers which can compile Java to JavaScript. As a last resort, you can use one of those compilers to take a JVML bytecode disassembler written in Java and compile it to JavaScript. One example of such a compiler is GWT.
Similarly, there are compilers which can compile JVML bytecode to JavaScript. Again, you can take one of the above JVML bytecode disassemblers written in Java, use any Java-to-JVML compiler (javac, ecj, gcj, …) to compile it to JVML (i.e. .class files), then compile those .class files to JavaScript.

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