Skip to main content

New Dart to JavaScript compiler ready for testing

Posted by Kasper Lund

We're getting close to replacing our old friend "frog"—the current
Dart-to-JavaScript compiler—with a new version called "dart2js". We've
built the new version with an emphasis on correctness and
compatibility with the Dart VM. This means that you can now take
advantage of some of the niceties of closures and code like this:

  main() {
    var closures = [];
    for (var i = 0; i < 8; i++) closures.add(() => i);
    for (var closure in closures) print(closure());
  }


will no longer print 88888888 when compiled to JavaScript, but
01234567 just like on the VM.

The new compiler is available in the latest continuous builds of the
Dart Editor and SDK. If you click on [Tools > Generate JavaScript] in
the editor menu, you'll see that we're automatically compiling your
code with both frog and dart2js allowing you to easily compare the
output:

 Generating JavaScript using frog...
 Wrote ...Sunflower.dart.js [103.0kb written in 1.9 seconds]
 Generating JavaScript using dart2js...
 Wrote ...Sunflower.dart.js_ [126.0kb written in 2.6 seconds]

We're actively working on making the output smaller and faster, so
expect improvements over the next weeks. If you want to try to use the
dart2js output in your web app, you need to change the <script> tag in
the HTML file to include the data-compiler="dart2js" attribute like
this:

 <script type="application/dart" src="..." data-compiler="dart2js"></script>

Writing a new compiler isn't completely trivial, and we're not done yet.
There are a few features remaining before we are at parity with the VM,
such as "support continue in switch statement" and
"support closures in initializer lists". 
As always we appreciate any feedback you
might be able to provide us with in the form of bug reports or e-mails
sent to the mailing list (http://www.dartlang.org/support/). If you
find that your project doesn't work when compiled with dart2js, we
really want to work with you to fix that.

For the technically interested, I can tell you that the new compiler
uses an internal representation in SSA form (static single assignment)
and that the compiler is implemented entirely in Dart.
Performance-wise it isn't highly tuned yet, but we feel like we have a
good infrastructure in place for interesting and effective
optimizations. We will keep you posted on our progress!

Cheers,
Kasper on behalf of the dart2js team

Popular posts from this blog

A stronger Dart for everyone

We are constantly asking ourselves:
How do we make developers even more productive when writing Dart apps? We believe that a critical part of the answer to this question is to make strongmode – a sound static type system for Dart – the standard for all Dart developers.

Teams that use Dart to build apps like Soundtrap, AdWords, AdSense, and Greentea say they really enjoy using strong mode features, such as early error detection. In fact, teams that have switched completely to strong mode cite not only early error detection but also better code readability and maintainability as major benefits. We hear this both from small teams and – even more so – from large teams with hundreds of developers writing and maintaining millions of lines of Dart code. As Björn Sperber from Soundtrap says,
Strong mode and the smooth integration with IntelliJ is a joy to use and a huge improvement. If you’ve tried out Flutter, you’ve already used strong mode checks from the Dart analyzer.

Given the benefits …

AngularDart 4

AngularDart v4 is now available. We've been busy since the release angular2 v3.1.0 in May. Not only did we "drop the 2", but we also improved the compiler and tightened up the framework to give you smaller code, we updated the package structure to improve usability, and we added several new features. Check out the updated documentation to get started.
Just angular Upgrading to v4 will require more than updating your version constraint. The package has changed names (back) to angular – dropping the 2. You'll need to update your pubspec.yaml and the corresponding imports in your code. In most instances, find-and-replace should do the trick. Going forward, the package will be called package:angular. We'll just update the version number.
Smaller code The updated compiler in 4.0 allows type-based optimizations that not only improve runtime performance but generate better code because we are able to strongly type templates. A big result of the update is that many ap…

Dart 1.24: Faster edit-refresh cycle on the web & new function type syntax

Dart 1.24 is now available. It includes the Dart Development Compiler and supports a new generic function type syntax. Get it now!


Figure 1: DDC debugging in Chrome.

Some notable changes in this release:
pub serve now has support for the Dart Development Compiler. Unlike dart2js, this new compiler is modular, which allows pub to do incremental re-builds for pub serve.In practice what that means is you can edit your Dart files, refresh in Chrome (or other supported browsers), and see your edits almost immediately. This is because pub is only recompiling your package, not all packages that you depend on.There is one caveat with the new compiler, which is that your package and your dependencies must all be strong mode clean.You can also use the new compiler to run your tests in Chrome much more quickly than you can with dart2js.Read more in the changelog.You can now publish packages that depend on the Flutter SDK to pub. Moreover, pub.dartlang.org has started tagging Flutter plugins with …