Dart SDK Quick Tour

(This is part 9 in an ongoing series about Dart. Check out part 8, This is this in Dart.)

The Dart team quietly started to provide binary Dart SDKs for download. Without compiling or syncing large source repositories, you can now compile your Dart code to JavaScript with Frog, run the Dart VM, and browse the Dart libraries.

Download

There are two options for downloading the Dart SDK: continuous nightlies or integration releases.

Choose the continuous builds if you want to live on the edge, or choose the integration builds if you want more tested releases.

For the SDK, look for either dart-linux.zip, dart-macos.zip, or dart-win32.zip. The other files (starting with DartBuild) are the Dart Editor.

After you download and unzip the archive, you'll have a dart-sdk directory. The bin directory has dart, which is the Dart VM, and frogc, the Frog compiler.

The Frog compiler

When Dart was initially announced, we shipped a DartC compiler which turned your Dart code into JavaScript code. DartC is written in Java, and is the compiler behind the Dart Editor. DartC supported incremental compilation (making the editor faster) but generated large JavaScript.

Some time later, the team released an experiment: a Dart to JavaScript compiler written in Dart itself. This compiler would generate essentially human readable, and terse, JavaScript. This Frog compiler (named after the Dart Frog) will generate only the JavaScript required to run the program, resulting in smaller output.

Running Frog

Assuming you have the following test.dart file:

main() => print("hello from dart!");

you can then compile it to JavaScript with the following command:

$DART_SDK/bin/frogc test.dart

which will generate the following JavaScript code:

//  ********** Library dart:core **************
//  ********** Natives dart:core **************
// ********** Code for Object **************
Object.defineProperty(Object.prototype, "toString$0", { value: function() {
  return this.toString();
}, enumerable: false, writable: true, configurable: true });
// ********** Code for top level **************
function print(obj) {
  return _print(obj);
}
function _print(obj) {
  if (typeof console == 'object') {
    if (obj) obj = obj.toString();
    console.log(obj);
  } else {
    write(obj);
    write('\n');
  }
}
//  ********** Library dart:coreimpl **************
// ********** Code for NumImplementation **************
NumImplementation = Number;
// ********** Code for StringImplementation **************
StringImplementation = String;
// ********** Code for _Worker **************
// ********** Code for top level **************
//  ********** Library test **************
// ********** Code for top level **************
function main() {
  return print("hello from dart!");
}
main();

The Dart virtual machine

One of Dart's primary language design constraints is that it must compile to effective and performant JavaScript. However, Dart is also designed to run in its own virtual machine, and a Dart VM is shipped inside the Dart SDK. You can use the Dart VM to run Dart code on the server or directly in a browser (with Chrome + Dart integration coming soon.)

Using the same test.dart file from above, we can run it directly on the command line with:

$ ~/Downloads/dart-sdk/bin/dart test.dart
hello from dart!

Startup for the Dart VM is very fast, too.

The libraries

The source code for the Dart libraries is also included in the SDK. You can browse the API docs at api.dartlang.org, but it's still fun to check out the actual source.

You'll find directories for the core libs, the DOM and HTML libs, and the frog compiler. You'll also see a directory named builtin, which includes runtime libraries like directories, file, sockets, and streams.

Summary

You can play with Dart today, without having to compile any code. The Dart SDK is now available for download, bundling the Frog compiler, the Dart virtual machine, and the source code for the libraries.

Next steps

Continue to part 10, Numbers in Dart.

Read more of my Dart posts, try Dart in your browser, browse the API docs, or file an issue request. Dart is getting ready, please send us your feedback!