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

Dart in 2016: The fastest growing programming language at Google, 2nd fastest growing in TIOBE Index

Dart was the fastest growing programming language at Google in 2016 with millions of lines of code written. It also made it to TIOBE Index Top 20 this month (see TIOBE's methodology).

It takes time to build something as ambitious as Dart and, in some ways, Dart is still in its infancy. But we're glad the hard work is starting to pay off.

Many thanks to our amazing community!

We're going to celebrate by ... releasing 1.22 next week (as per our usual 6 week release schedule).

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 2.1 and new Components

AngularDart got its own dedicated team 5 months ago. Last month, we launched 2.0 final on the Dart Developer Summit. Today, we’re releasing the first minor release after that: 2.1.

Since the focus of AngularDart is Productivity, Performance, Stability, there are no major breaking changes (see the changelog) — but a lot of behind-the-scenes improvements. Your apps will get slightly smaller and faster (even relative to 2.0 which already made huge strides in size and performance since the compiled-from-TypeScript days).

Many features that AngularJS had to implement for JavaScript and TypeScript are not needed in Dart (because Dart already has those features out-of-the-box). So we’re removing them from AngularDart. Renderer is deprecated in favor of plain-old dart:html. NgPlural is going away — Dart programs can use the package:intl library.

New components

On the Dart Developer Summit, we launched AngularDart Components — the material design widgets Google is using in customer-facing apps …