Java (via GWT) vs Dart

That's Java, so it is strongly typed, and we can use fully the IDE: error detection, refactoring, auto-completion, etc.

Perfect if you have a strong background in Java programming, and need to code for the client side.

Because Java is statically typed, integrated development environments (IDEs) for Java can provide a lot more feedback on errors you will encounter. Java IDEs can give you specific errors in the location where they occur without having to run the code every time. This makes is faster to debug and learn from your mistakes.

IDEs also have extensive auto complete capabilities that can help you learn the programming libraries you are using faster and tell you what functions are available.

Java is one of the most popular languages in industry, consistently ranking either first, or occasionally second (behind C or Javascript) in terms of usage. Polls (see sources below) show it to be consistently in high demand, particularly as measured by job board postings. This makes Java a great time investment, as you will be easily able to get a job utilizing your skills, particularly as those Java applications in production now will continue to need maintenance in the future. It also results in great support for tools and plenty of computer science books, example projects and online tutorials.

Most Java code follows very standardized coding styles. This means that when you're starting out, there are fewer questions about how you should implement something as the programming styles and patterns are well established and consistent. This consistent style means that it's often easier to follow others' example code, and that it's more likely to meet at least a certain minimum standard of quality. This discipline with consistent stylistic standards also becomes useful later, when collaborating on projects with larger teams.

Produced JS is highly optimized, can be separated in modules with lazy loading, can be internationalized while loading only the chosen language.

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.

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.

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.

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.

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.

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.

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.

Strong mode applies a more restrictive type system to Dart to address its unsound, surprising behavior in certain cases.

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.

Dart to Javascript compiler (dart2js) generates very high quality source code with very high optimization. The output code is also very readable and easy to understand.

Dart does not just compile to JavaScript, it also compiles to native code on mobile platforms like iOS and Android as demonstrated by flutter.io