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Comment by mistercow | Hacker News Reader

>Dart interops with JavaScript...but it's not JS. It doesn't even use the JavaScript number type for example.

What is meant by this? As far as I know, the only way that you can use Dart in any browser currently is by compiling it to JS, and when you do that it most certainly does use native JS numbers. In fact, the type check function it creates for numbers contains this line:

      if (!(typeof value === 'number')) {

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He means that the semantics of Dart - including the data types provided by Dart - are different from JavaScript. This is in opposition to TypeScript, which is a superset of JavaScript, which means that it necessarily shares JavaScrips semantics.

If your example bothers you, consider that JavaScript just happens to be a target language for the Dart compiler. That is, it takes a program with Dart's semantics, and figures out how to map those to JavaScript semantics. That there is a mapping is not all that interesting, as such a mapping will exist from any Turing complete language to any other.

Really? Wow, that's cool. Can I have a reference?

I'm really just describing how a compiler works. Are you looking for references on the compilation process? There's a classic series called "Let's Build a Compiler" (http://news.ycombinator.com/item?id=1727004) available online that walks through building a simple compiler. Then there's also actual textbooks, but I was not impressed with either of the two textbooks I've had on the topic. Many people recommend "Compilers: Principles, Techniques, and Tools" (http://dragonbook.stanford.edu/) also referred to as just the dragon book. If you're not averse to textbooks, you may also want to check out Michael Scott's "Programming Language Pragmatics" (http://www.cs.rochester.edu/~scott/pragmatics/).

The native Dart VM distinguishes between integers and floats for performance reasons, and (I think) lets you explicitly cast back and forth between them, and if, at some point, Chrome ships a Dart interpreter, developers will be able to take advantage of that. I assume this all gets turned into noops when it's translated to JS, so to some extent it's academic, but I think they were just trying to illustrate that Dart's innate notions of built-in types are different than JS's, and are kludged into JS types at compile time, whereas TS sits much closer to current JS environments.

There is an experimental build of Chromium called Dartium that contains a Dart VM. It isn't practical for daily use, but it's a taste of things to come.

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