When comparing Scala.js vs C#, the Slant community recommends C# for most people. In the question“What is the best language to use simultaneously for front and back end?” C# is ranked 5th while Scala.js is ranked 6th. The most important reason people chose C# is:
.NET offers rich functionality.
Ranked in these QuestionsQuestion Ranking
Pro Type inference
Scala offers type inference, which, while giving the same safety as Java's type system, allows programmers to focus on the code itself, rather than on updating type annotations.
Pro Immutable values
The immutable values make it perfect for working with concurrency.
Pro Extensive standard libraries
Scala.js implements most of the Scala standard library and many parts of the Java one. Among others, it supports Scala's rich collection library.
Pro Implements a mature language
In contrast to other options, Scala.js is a compiler plugin for an already existing and mature language: Scala.
As such, it benefits automatically from the existing compiler, from the language design choices made for Scala, which exists and is established in the industry since years.
Pro The strength of Scala on the server
The strength of Scala (JVM) on the server can not be underestimated, and is probably superior to any other choice listed here (where applicable; many have no server-side equivalent).
Being able to use such a powerful language (and ecosystem) on the server AND on the client, and sharing code between the two, is a big advantage.
Because Scala.js is a plugin to the Scala compiler, the whole power of the Scala language is available at compile-time. Which includes macros. Very expressive things can be done, in a type-safe way, which are difficult or impossible in other languages.
Pro Dead-code elimination
Scala.js performs dead-code elimination out of the box (when running in the "fullOpts" mode).
Scala supports both Functional and Object Oriented styles of programming. Beginners can learn both paradigms without having to learn a new language, and experts can switch between the two according to what best suits their needs at the time.
Keeps your client and server sources in sync.
Pro Incremental compilation
Through SBT, Scala.js supports incremental compilation out of the box. That is: SBT automatically picks-up the changes (think "watch" in other tools) and only recompiles what is needed.
This makes the development cycle fast and very pleasant to work with.
Pro Excellent tooling (IDE) support
The same good and mature tooling that can be used for Scala can be used for Scala.js out of the box (code-completion, refactoring, immediate feedback, etc.).
.NET offers rich functionality.
Pro 3rd Party support
Lot's of tools and libraries available.
Pro Visual Studio
The Visual Studio IDE offers one of the best development environments. The Community Edition can be used for free.
Pro Can be used in a variety of fields
with Xamarin for Mobile (ios, android)
with .net core asp for server (linux, windows)
with .net core for desktop (windows, mac)
with mono for desktop (windows, linux)
with blazor for web client with webassembly.
However, it is not considered top for any of those categories
top choice for windows desktop with .net framework
top choice for Unity
.net 5 will unify frameworks similar to JVM (just one)
Runs on Linux, Mac, and Windows
Can be designed visually with the Visual Studio designer for traditional Windows forms, WPF, or Web forms.
Pro It is a C like language.
Being a C like language counts in favor for it as a general purpose programming language, given the ease of using existing skills to pick up this language easily.
there are other superior languages that could be used as a general purpose, such as: F#, Haskell, but the complexity of those languages, being functional, make them strange to the usual C Syntax.
C# is better than C whenever garbage collection, Objects, classes, data access, are needed. But C is going to be the choice when hardware access and performance are paramount.
Con Can be intimidating for beginners
Scala is an industrial language. It brings functional programming to the JVM. All books/tutorials cover friendly aspects of Scala, but there are corners of the language that one can wander into that are not friendly to beginners.
Con A complex language with a lot of incidental complexity that results in significant mental overhead
Con Combines OOP and functional programming for a hodge-podge paradigm
Its excellent mix of functional and OOP programming just like Python to use the tool best suited
Con Learning curve
For a beginner the .NET framework can be daunting, the rich functionality means that things often can be done in several ways.
Con Microsoft will mess up with the Visual studio installation
And all of a sudden you'll need to reinstall the entire thing just because it stopped working.
Microsoft assumes that every workstation is connected to the Internet then it is always pushing updates.
Con Very large runtime
Cannot be used for embedded programming