Dart 1.5

Not sure what you mean: MS has a history of abandoning its developer platforms and frameworks that thier developers have invested in, so much so that there's no longer a clear UI story for building native desktop windows apps, i.e. VB6, Silverlight, WinForms and WPF are all effectively deprecated. Although they have long support life, when they officially abandon a platform they also refuse to Open Source it so others can keep it alive (e.g. VB6 http://bit.ly/KPMUS6). I personally can't see how anyone can put trust into building native Windows desktop apps (i.e. over web apps) given the repeated a history of abandonment.

Even the #1 feature for VS.NET is to continue developing very popular XNA framework: http://visualstudio.uservoice.com/forums/121579-visual-studi...

Likewise on the server side there's been history of deprecated frameworks a lot of developers have invested a lot of energy into learning, e.g: .asmx, CSF, WCF, WCF/REST, WSE, WCF DataServices, RIA

Whilst VisualStudio is a great IDE, I find it a subpar experience without R#. The major advantages Dart has over C# is that it still provides an enjoyable experience to develop even without an IDE which also includes support for the most popular text editors: https://www.dartlang.org/tools/ If you like IDE and tooling support, the DartEditor offers a good experience with built-in analyzer, debugging and refactoring support you can expect from a well engineered language.

By contrast, C#'s configuration model, msbuild project format, heavy frameworks and tooling makes it unfeasible to develop without an IDE.

The other major advantage Dart has is that it compiles down to JS where even the compiler is completely self-hosting and runs inside a browser without plugins: http://try.dartlang.org/ Being able to share the same code on client and server and having a single integrated development full-stack experience is a huge win in re-usability and utility.

Another killer feature is that the language and tooling is cross-platform which supports Windows, OSX and Linux. Something .NET devs often miss out on is the value and utility of being able to host apps on cost-effective Linux servers.

Google continues to invest a tonne of resources in Dart and Polymer which are massive undertakings that are providing a much simplified and consistent experience for developing large, complex web apps. Nothing like Dart or Polymer exists. Dart is a platform that transpiles to JS, includes a native Dart VM, an entire toolchain including IDE, analyzer and debugger both in Dart Editor as well as in Chrome, in both the Dart VM as well as debugging with Source maps.

The worlds best VM engineers work on the Dart VM, i.e. the same pedigree responsible for the StrongTalk VM that was later acquired by Sun to form the basis of the world-class Java Hotspot VM that later went on to develop V8, are now leading the development on the Dart VM.

The excellence shows itself in the consistency and minimalism goals in the language, providing a productive, iterative dynamic language experience for fast prototyping with the benefit of static analysis with optional typing when scaling up to a maintainable, well-documented code-base (best of both worlds).

Not only is Dart a productive dynamic language, it also has excellent performance, the best performance of all languages I benchmarked with a port of Peter Norvig's Sudoku solver: https://github.com/dartist/sudoku_solver#benchmarks

re: GWT. GWT is still actively developed and making progress. I just talked with some GWT team members at I/O, and they're adding better JS-interop (like we are), incremental compilation, and are looking at web components support. One thing we talked about that would be nice is GWT-Dart interop, (if we get everything else done).

I'm biased, being on the Dart team, but I think Dart is a much nicer language that Java, so I would choose Dart for a new project. GWT might still be a good choice though if you have a large existing investment in Java that you can repurpose in the client. Many enterprises have hundreds of thousands or millions of lines of Java code that aren't going anywhere anytime soon.

So, should you think about Dart? I guess that depends on how ready or willing you are to migrate your code away form Java. If you were thinking about rewriting in JavaScript, then I'd definitely say consider Dart. If you're happy with Java and GWT, then you can keep going that direction.

The main thing I miss from Swift is its extensibility letting you extend primitive types like Arrays or Strings, this lets you easily add LINQ-like capabilities even tho Swift doesn't ship with many, see: https://github.com/mythz/swift-linq-examples

Dart comes with a rich functional and Stream API's on collections so most of the time you wont need to extend it (same LINQ examples in Dart: https://github.com/dartist/101LinqSamples), but unfortunately you can't extend built-in (or external) types which means you need to use top-level methods which can break-up the flow of your beautiful expression flows. Extensions is also important for minimizing unnecessary abstraction and maximizing re-usability since you can extend without being forced to create foreign wrapper API's.

IMO Extensions are one of the most important traits for keeping a minimal friction-free language, something I see Go and Swift benefiting a lot from.

Dart does have powerful mixins (https://www.dartlang.org/articles/mixins/) but you can only mixin into classes you define (i.e. not built-in or external types).

But otherwise I find Dart's optional-typing a tonne more productive than Swift's strict type inference / generic enforcement, Dart also has a rich consistent library, integrated package manager, static analyzer and overall better development experience.

Although there's little overlap as Swift is mainly for creating iOS/OSX desktop apps and Dart is focused on rich Web Apps. Basically the only times when you'd be able to choose one or the other is in command-line scripts, I'd still prefer to use Dart for.

How practical is today to start with Dart for web apps instead of Javascript? speaking from someone who doesn't know JS.

Wow, seriously? I've been using Beta and not noticed any breakage (but that doesn't mean there isn't any). Do you have any more context?