Chapter 1. Quick Start

Google cares a lot about helping to make the web great. We write a lot of web apps, many of them quite sophisticated—think Gmail, Google Calendar, Google+, and more. We want web apps to load quickly, run smoothly, and present engaging and fun experiences to users. We want developers of all backgrounds to be able to build great experiences for the browser.

As an example of Google’s commitment to the web, consider the Google Chrome browser. Google created it to spur competition at a time when the web platform seemed to be stagnating. It worked. As Figure 1.1, “Browser speed (V8 benchmark suite v7; higher numbers are better)” shows, browser speed has increased immensely since Chrome’s introduction in 2008.

Figure 1.1. Browser speed (V8 benchmark suite v7; higher numbers are better)

The number of new features in browsers has also increased, with APIs such as WebGL, FileSystem, Web workers, and WebSockets. Browsers now have automatic update capabilities, frequently delivering new features and fixes directly to the user. Mobile devices such as tablets and phones also have modern browsers with many HTML5 features.

Despite these improvements in the web platform, the developer experience hasn’t improved as much as we’d like. We believe it should be easier to build larger, more complex web apps. It’s taken far too long for productive tools to emerge, and they still don’t match the capabilities offered by other developer platforms. You shouldn’t have to be intimately familiar with web programming to start building great apps for the modern web. And even though JavaScript engines are getting faster, web apps still start up much too slowly.

We expect Dart to help in two main ways:

It’s hard to talk about a language without seeing it. Here’s a peek at a small Dart program:

lang-dart
import 'dart:math';

class Point {
  num x, y;
  Point(this.x, this.y);
  num distanceTo(Point other) {
    var dx = x - other.x;
    var dy = y - other.y;
    return sqrt(dx * dx + dy * dy);
  }
}

main() {
  var p = new Point(2, 3);
  var q = new Point(3, 4);
  print('distance from p to q = ${p.distanceTo(q)}');
}

Of course, Dart’s main use case is building modern web apps. Programming the browser is easy:

lang-dart
import 'dart:html';

main() {
  var button = new ButtonElement();
  button..id = 'confirm'
        ..text = 'Click to Confirm'
        ..classes.add('important')
        ..onClick.listen((e) => window.alert('Confirmed!'));
  query('#registration').children.add(button);
}

You’ll learn about the Dart language and libraries in Chapters 2 and 3 respectively.

Dart may look familiar, but don’t let that fool you. Dart has lots of cool features to help give you a productive and fun experience building the next generation of awesome web apps.

Dart is easy to learn. A wide range of developers can learn Dart quickly. It’s an object-oriented language with classes, single inheritance, lexical scope, top-level functions, and a familiar syntax. Most developers are up and running with Dart in just a few hours.

Dart compiles to JavaScript. Dart has been designed from the start to compile to JavaScript, so that Dart apps can run across the entire modern web. Every feature considered for the language must somehow be translated to performant and logical JavaScript before it is added. Dart draws a line in the sand and doesn’t support older, legacy browsers.

Dart runs in the client and on the server. The Dart virtual machine (VM) can be integrated into a web browser, but it can also run standalone on the command line. With built-in library support for files, directories, sockets, and even web servers, you can use Dart for full end-to-end apps.

Dart comes with a lightweight editor. You can use Dart Editor to write, launch, and debug Dart apps. The editor can help you with code completion, detecting potential bugs, debugging both command-line and web apps, and even refactoring. Dart Editor isn’t required for writing Dart; it’s just a tool that can help you write better code faster.

Dart supports types, without requiring them. You can omit types when you want to move very quickly, aren’t sure what structure to take, or simply want to express something you can’t with the type system. You can add types as your program matures, the structure becomes more evident, and more developers join the project. Dart’s optional types are static type annotations that act as documentation, clearly expressing your intent. Using types means that fewer comments are required to document the code, and tools can give better warnings and error messages.

Dart scales from small scripts to large, complex apps. Web development is very much an iterative process. With the reload button acting as your compiler, building the seed of a web app is often a fun experience of writing a few functions just to experiment. As the idea grows, you can add more code and structure. Thanks to Dart’s support for top-level functions, optional types, classes, and libraries, your Dart programs can start small and grow over time. Tools such as Dart Editor help you refactor and navigate your code as it evolves.

Dart has a wide array of built-in libraries. The core library supports built-in types and other fundamental features such as collections, dates, and regular expressions. Web apps can use the HTML library—think DOM programming, but optimized for Dart. Command-line apps can use the I/O library to work with files, directories, sockets, and servers. Other libraries include URI, UTF, Crypto, Math, and Unit test.

Dart supports safe, simple concurrency with isolates. Traditional shared-memory threads are difficult to debug and can lead to deadlocks. Dart’s isolates, inspired by Erlang, provide an easier to understand model for running isolated, but concurrent, portions of your code. Spawning new isolates is cheap and fast, and no state is shared. In web apps, isolates even compile to Web workers.

Dart supports code sharing. Traditional web programming workflows can’t integrate third-party libraries from arbitrary sources or frameworks. With the Dart package manager (pub) and language features such as libraries, you can easily discover, install, and integrate code from across the web and enterprise.

Dart is open source. Dart was born for the web, and it’s available under a BSD-style license. You can find the project’s issue tracker and source repository online. Maybe you’ll submit the next patch?

Now that you know something about Dart, get ready to code! These instructions feature the open-source Dart Editor tool. When you download Dart, you not only get Dart Editor, but also tools such as the Dart-to-JavaScript compiler and a version of Chromium (nicknamed Dartium) that includes the Dart VM.

Step 2: Launch the Editor

Go to your Dart installation directory, and double-click the DartEditor executable file .

You should see the Dart Editor application window appear, looking something like Figure 1.2, “Dart Editor and its Welcome page”.

Figure 1.2. Dart Editor and its Welcome page