Showing posts from April, 2013

Lazy Load Libraries in Dart

UPDATE: This article is now DEPRECATED, but the feature lives on! Dart now formally supports lazy loading (deferred) libraries. Learn more in the Deferred Loading in Dart article.

Dart is a statically analyzable language, and its tree-shaking compiler does a good job of eliminating dead code and producing a single, optimized application file. However, sometimes developers need to control when certain libraries are loaded and thus need to control which libraries are included in the main application file. To help, the dart2js compiler, which converts Dart code into JavaScript code, now supports lazy-loaded libraries.

Lazy Load

As an example, consider an application that has many different screens. Some screens are more obscure than others, and aren't required for the application to start. A developer should be able to say "I don't need these screens now, but pull them in when I do need them." This lazy-loading is a common deployment strategy for web apps, because small in…

Dynamically Load Code with Dart

Rejoice! Dartium, a build of Chromium with the Dart VM, can now spawn a new isolate from a URI. This means your Dart apps have a new option for more modular code.


In Dart, an isolate is an abstraction for an "isolated memory heap". Isolates do not share memory (variables, statics, etc), they are essentially self-contained applications. Isolates communicate by sending and receiving messages over ports.

Why Isolates Matter

Dart programs are static, in that their shape and structure do not change after they are compiled. A static program is great for optimizations like tree shaking (aka dead code elimination), type-inferencing compilers, and more.

However, modular apps often require a way to dynamically load code. Configurable and modular apps need a way to, at run time, pull in new functionality. If Dart apps have a static structure, how can they dynamically alter their behavior?

Isolates to the rescue! The structure inside of an isolate is static, but a Dart program is…

6 Dart FAQs - Answered!

Calvin Prewitt wrote some good questions about Dart via G+. It might be hard to find his questions and my answers, so I hoisted them here. Enjoy!

Q) Could you also detail compatibility and which JavaScript APIs are fully or partially supported for Dart2JS production code?

A) All JavaScript APIs supported by Chrome should be available to Dart. See

Q) It appears Dart is aiming to eventually replace it? The FAQ says it only targets modern browser versions.

A) Dart's aim is to give developers like you a very productive experience, and give your users a very fast experience. Dart targets IE9+, plus the modern versions of Firefox, Chrome, Safari, mobile safari, and Chrome for Android. Basically, modern browsers.

Q) Is there a way to have fine grained control over the JS code like in Closure?

A) Dart2js can emit a single file, plus up to one other lazily loaded library. In the future, we want to give you more control. Here's the bug: http…