Kathy Walrath - What is Dart?: A new language for building structured web apps

Copyright 2012

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We want you to be able to create great web apps. Great web apps improve the web, and when the web does better, everyone wins.

Engineers at Google have been thinking about web apps for a long time. Weve written a bunch of complex and widely used large-scale web apps (think Gmail, Google+, and Google Docs), so were quite familiar with the challenges of architecting web apps. Weve also written a browser (Chrome) and a JavaScript engine (V8), so weve thought a lot about how to make web apps run faster.

Basically, we created Dart because we think itll help bring more great apps to the web, and we think it should be easier to create more complex web applications.

App developers from all platforms should be able to build for the modern web, but many non-endemic web developers have different expectations and requirements from their language, tools, and development platform than what is available today. We believe there is room for a new platform, one that is not encumbered by 15 years of cruft, that is familiar to developers of different backgrounds, and that is structured to enable the larger, more complex apps that users are demanding.

We dont think JavaScript is going away. In fact, Google is actively working with TC39 to improve JavaScript, and new features are already landing in V8 and Chrome. However, our commitment to improving JavaScript doesnt prevent us from thinking about other solutions. For example, Dart will take advantage of the continued work on JavaScript, because Dart programs compile to JavaScript to run across the entire modern web.

We believe Dart is a compelling and familiar platform that meets the needs of developers from different backgrounds and experiences, including endemic web developers. We believe that Dart brings fresh ideas to web programming, and that innovation in both Dart and JavaScript will help push the web forward for app developers and users.

Show Me the Code

Enough talk, lets see some code. Whether you know JavaScript or Java, Dart code should look familiar. Heres an example of a simple web page in Dart:

hi.dart:

#import('dart:html');main() { document.query('#status').text = 'Hi, Dart';}

hi.html:

...

...

Now lets look at some Dart code that uses functions:

send(msg, to, from, [rate='First Class']) { return '${from} said ${msg} to ${to} via ${rate}';}main() => print(send('hello', 'Seth', 'Bob'));> "Bob said hello to Seth via First Class"

The => syntax used to implement main() is a nice, compact way to implement a function that evaluates and returns a single expression. Without =>, the implementation of the main() method would look like this:

main() { print(send('hello', 'Seth', 'Bob'));}

In the send() method implementation above, rate is an optional parameter with a default value. That method also illustrates string interpolation at work (${var}).

Heres some Dart code thats more object-oriented:

class Point { Point(this.x, this.y); distanceTo(other) { var dx = x - other.x; var dy = y - other.y; return Math.sqrt(dx * dx + dy * dy); } var x, y;}main() { var p = new Point(2, 3); var q = new Point(3, 4); print('distance from p to q = ${p.distanceTo(q)}');}

This code should look pretty familiar if youve ever used a class-based language.

How Can I Play with Dart?

The easiest way to try out Dart is to use Dartboard, a way to execute Dart code interactively in any modern browser. Dartboard is embedded in the Dart site, at www.dartlang.org. You can also use Dartboard by going directly to try.dartlang.org. Heres a picture of what youll see on that site:

Change the code as you like, and then click the Run button (at the upper left). Youll see the results of your code in a new area below:

The URL at the upper right of the Dartboard is a link to the code you just ran.

Like most things related to Dart, Dartboard is still changing. For the latest information, see the Dartboard tutorial.

How About a Real Editor?

When you outgrow Dartboard, try Dart Editor. Its a downloadable editor for Windows, Mac, and Linux that lets you write, modify, and run Dart web apps. Dart Editor can run your Dart code via the VM, or it can compile it to JavaScript and launch it in your browser. Heres a picture of what Dart Editor currently looks like: