Dart is a single threaded programming language. So if any piece of code blocks the execution of the program, the program practically freezes. To avoid this Dart makes use of asynchronous operations which let your program run without getting blocked. This is done through Future objects. A Future is an object which represent a means for getting a value at a certain point in the future. A function may invoke a Future and when that happens, two outcomes can be achieved: 1. The function is unable to return a value, so it queues up work to be done and returns an uncompleted Future object. 2. Or later when a value is available to be returned, the Future object completes with that value.
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Pro Great async language support
Dart is a single threaded programming language. So if any piece of code blocks the execution of the program, the program practically freezes. To avoid this Dart makes use of asynchronous operations which let your program run without getting blocked. This is done through Future objects.
A Future is an object which represent a means for getting a value at a certain point in the future. A function may invoke a Future and when that happens, two outcomes can be achieved:
- The function is unable to return a value, so it queues up work to be done and returns an uncompleted Future object.
- Or later when a value is available to be returned, the Future object completes with that value.
Pro Great standard library
Dart includes a truly comprehensive core library, making it unnecessary to include disparate, external resources for basic functionalities Other than reducing the need to pull in various 3rd-party utilities this also ensures that all Dart code looks and feels the same.
Out of the box, the developer gets core libraries to help with: async, collections, strings, regexps, conversions, formats, file I/O, math, typed data, and more.
Pro No compile time in development
Dartium (Chromium derivative) is a browser with integrated Dart VM, which allows you to run and debug native Dart code during development for short edit-reload cycles. Only for testing on other browsers and deployment is transpiling to JS necessary.
Pro A lot of tools are available to help in developing with Dart
Dart has a lot of tools available which help with developing Dart applications. Some examples of those tools include:
- pub - package and dependency management and build tool
- analyzer - static syntax analysis with linter, quick fixes, autocompletion support for easy IDE integration
- test - powerful and flexible testing framework and test runner
- dev_compiler - generate reusable JS instead of tree-shaken minified JS output (work in progress)
- dartfmt_ - source code formatter
- server-side VM
- observatory - a powerful tool for profiling and debugging running Dart code (for Dartium and Dart server code)
In Dart many browser differences (subtle differences and also missing features) are abstracted away or polyfilled. When Dart is transpiled to JS the output works on all supported browsers. There is usually no need to load polyfills or to consider browser differences during development. No need for libraries like jQuery to make the same code work the same on all browsers.
Pro Will be familiar to Java developers
The language will look familiar to Java developers, easing the learning curve.
And yet, while it's similar, it has some nice syntax facilities to avoid common boilerplate code found in Java. Code is terser, yet readable.
Pro Easy prototyping
Dart has an optional type system which makes Dart a great language for prototyping. It encourages developers to gradually evolve their programs without worrying about types first.
Pro Can compile to efficient machine code
Dart was designed to be as expressive as possible. Ahead-of-time compilers can compile Dart code to efficient machine code. This is especially important when deploying to mobile where you don't want (or can't) use a JIT.
Pro AngularDart 2.0 support
Pro Optional strong mode.
Strong mode applies a more restrictive type system to Dart to address its unsound, surprising behavior in certain cases.
Pro Support of semi-coroutines (generators)
Generators, also known as semicoroutines, are also a generalization of subroutines.
Generators are primarily used to simplify the control of iteration behavior of a loop, the
yield statement in a generator passes a value back to a parent routine.
A generator is very similar to a function that returns an array, in that a generator has a certain number of values. But instead of building and returning an array that contains all the wanted values, a generator returns them one at a time, this saves memory and allows the caller function to start processing the first few values immediately.
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.).
Con Dart SDK does not provide standard (out of the box) way to access SQL-based databases on server side
This missing (but very popular) feature requires to use 3rd-party packages developed by the personal enthusiasts or very small groups of enthusiasts, which is not very convenient because they are all very fragmented in terms of content, the essence and capabilities.
Con Small community, little momentum
Con A complex language with a lot of incidental complexity that results in significant mental overhead
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 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