GWT

This is a beta version. If you find errors, please report them or change them!

Ray Cromwell, Senior Software Engineer
Updated June 2012

Elemental is a new library for fast, lightweight, and "to the metal" web programming in GWT. It's intended for developers who are comfortable working with the browser API's that JavaScript programmers use. We think it will be an excellent 'thin' library for both mobile and desktop web applications.

What's In It?

Elemental includes every HTML5 feature, including DOM access of course, but also bleeding edge features like WebGL, WebAudio, WebSockets, WebRTC, Web Intents, Shadow DOM, the File API, and more. We can do this because we generate Java code directly from the WebIDL files used by JavaScript engines.

Elemental also includes high-performance collections and a new JSON library. These libraries work equally well in a browser or in a server (JVM) environment.

Performance

Elemental is designed to allow the GWT compiler to generate high-performance JavaScript with no overhead. It does this by using only JavaScript overlay types.. Also, the collection classes map directly to underlying JavaScript collections with no overhead.

Example Usage

Elemental uses Java interfaces to hide most of the generated overlay types it uses. JS APIs instances can be obtained by the Window or Document interfaces. Here is a simple example to play a sound using the Web Audio API.

package com.myapp;
import elemental.client.*;
import elemental.dom.*;
import elemental.html.*;

public class ElementalExample implements EntryPoint {
  public void onModuleLoad() {
    Window window = Browser.getWindow();
    AudioContext audioContext = window.newAudioContext();
    Oscillator osc = audioContext.createOscillator();
    osc.setType(Oscillator.SQUARE);
    osc.connect((AudioParam) audioContext.getDestination(), 0);
    osc.getFrequency().setValue(440.0f);
    osc.noteOn(0);
  }  
}

In general, HTML elements can be constructed by invoking methods starting with the pattern Document.createXXXElement where XXX could be elements like Select, or Video. JS APIs which allow the new keyword to construct instances are found on Window.newXXX where XXX represents the underlying Javascript constructor name.

Caveats

Elemental is a work in progress. Due to the nature of it being auto-generated from IDL specifications, and those specifications for HTML5 changing rapidly over time, there are no unit tests for generated code, and usage of bleeding edge HTML5 are untested and may break.

Elemental also introduces a new set of native JS collections which are not interoperable with Java Collections.

Currently, Elemental is generated from the WebKit IDL files and contains many references to vendor-prefixed browser extensions. Using these draft-spec extensions may result in code that doesn't work on Firefox, Opera, or IE. Later versions of Elemental will include shim-generation to force generated code to use the non-vendor prefixed APIs across all browsers.