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Thursday, April 10, 2008

An idea for Dojo from GWT land

Now that I'm at Google I've been getting a bit more exposed to GWT (the Google Web Toolkit). I used to dismiss it because I'm a JavaScript hacker and GWT is in Java-land, but I've been learning some interesting things about it that I think could help in Dojo-land if we adopted them.

Ray Cromwell rolled something called GQuery, which is basically JQuery inside of GWT. What is unique is you can do JQuery style selectors inside of Java. Dojo has this as well, with dojo.query, but what Ray is doing is crazy. Because GWT gets compiled, he can turn something like this:


into this:


in the source. Here's Ray describing it:

"GQuery is progressing nicely. I implemented all of CSS3 selectors by following ExtJS's DomQuery implementation, only I added the ability to parse at runtime as well as via a generator at compile time. The compile time generator turns a CSS selector into 100% inlined code. That is, a selector like "#foo", will turn into "return document.getElementById("foo");", no parsing step involved. I've still got a bunch of optimizations to make, add support for XPath and native getElementsByClassName, but even now working with the library in GWT is very cool. I just started looking at DomAssistant as well, to incorporate (i.e. steal) the best algorithms from each."

One of the comments sums up the benefits of this nicely:

"You have an unfair advantage; since your selectors are compiled you can do any number of optimizations to them, and basically beat any other selector engine out there."

GWT itself does some interesting optimizations like this around what code is sent to specific browsers. I'm seeing numbers that blow me away, that because you can only send down the code needed for a specific browser you can really slim things down. For example, something like Dojo GFX has code paths for IE (VML), Firefox (SVG), and Safari (Canvas). If we could just send which one you need then the code would be 1/3 the size.

How can we get these kinds of benefits in Dojo? We already have a build time that runs through a JavaScript interpreter; can we start to do magic like this? The performance and size benefits I'm seeing in the GWT-world seem to indicate that it is useful.

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