NW.js under the hood

As we stated in the introduction, NW.js, made by Roger Wang of Intel's Open Source Technology Center (Shanghai office) in 2011, is a web app runtime based on Node.js and the Chromium open source browser project. To understand how it works, we must first analyze its two components:

• Node.js is an efficient JavaScript runtime written in C++ and based on theV8 JavaScript engine developed by Google. Residing in the operating system's application layer, Node.js can access hardware, filesystems, and networking functionalities, enabling its use in a wide range of fields, from the implementation of web servers to the creation of control software for robots. (As we stated in the introduction, NW.js has replaced Node.js with io.js from version 0.12.0.)
• WebKit is a layout engine that allows the rendering of web pages starting from the DOM, a tree of objects representing the web page. NW.js is actually not directly based on WebKit but on Blink, a fork of WebKit developed specifically for the Chromium open source browser project and based on the V8 JavaScript engine as is the case with Node.js.

Since the browser, for security reasons, cannot access the application layer and since Node.js lacks a graphical interface, Roger Wang had the insight of combining the two technologies by creating NW.js.

The following is a simple diagram that shows how Node.js has been combined with WebKit in order to give NW.js applications access to both the GUI and the operating system:

In order to integrate the two systems, which, despite speaking the same language, are very different, a couple of tricks have been adopted. In the first place, since they are both event-driven (following a logic of action/reaction rather than a stream of operations), the event processing has been unified. Secondly, the Node context was injected into WebKit so that it can access it.

The amazing thing about it is that you'll be able to program all of your applications' logic in JavaScript with no concerns about where Node.js ends and WebKit begins.

Today, NW.js has reached version 0.12.0 and, although still young, is one of the most promising web app runtimes to develop desktop applications adopting web technologies.