Chapter 5
Dart and JavaScript

When Dart first came out, every major browser vendor, as well as the WebKit project, announced that they had absolutely no intention of embedding the Dart VM in their browsers. Many bristled at the very suggestion that a nonstandard language^[9] be supported even obliquely. How another language was supposed to become a standard seemed a tricky question. Fortunately, Google had a plan.

In the grand tradition of CoffeeScript,^[10] the Dart project includes a compiler capable of compiling Dart into JavaScript. The goal is that, even if Dart does not become an overnight standard, web developers tired of the quirks of JavaScript have a choice. We can now code in a modern language for the Web but still support the wide variety of browsers on the market.

The JavaScript generated by the Dart compiler includes shim code for the various Dart libraries. There is generated JavaScript that translates Dart DOM calls into JavaScript. There is generated JavaScript that supports Dart Ajax. For just about every feature of Dart, there is a corresponding chunk of JavaScript that gets included in the compiled output.

If that sounds large, well, it is. When first released, the compiler generated tens of thousands of lines of JavaScript!

Of course, the compiler continues to improve. It now supports compression/optimization and is producing JavaScript libraries in the range of thousands of lines of code instead of tens of thousands. Considering that Dart does a good chunk of the work of many JavaScript libraries like jQuery, this is already a good start. And it is only going to get better.