One of the frequently expressed frustrations with JavaScript, especially from users coming from more static languages, is the lack of typing capabilities in JavaScript. Typing provides the ability to define and enforce contracts between interfaces such that interactions can be validated before violated assumptions result in later difficult-to-find bugs. On the other hand, many users that have grown fond of JavaScript have come to enjoy the fast and free style, and the minimalism of simply defining behavior without needing to make extra type definitions. However, these two coding preferences do not need to be mutually exclusive.

The abandoned ES4 effort made a valiant attempt to add typing (without losing dynamism) via gradual typing; however this still demanded the inclusion of intrusive typing annotations—thus adding type constraints to code polluted the otherwise simple direct JavaScript programming style necessitating more complex, difficult-to-follow code. Other efforts include libraries to define types on functions without extending syntax.

It is now possible to unobtrusively define type constraints on properties and methods in JavaScript with portable JSON schema based definitions called JSON schema interfaces (JSI). JSI is a typing system for JavaScript that does not force any new syntax on JavaScript. Schema structures can be used to define the type constraints in a way that works with existing JavaScript classes and objects.

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During the interaction design phase, we determined that Netflix’s current drag and drop reordering feature was well thought out — so we set out to create the same reordering behavior in Queued. As Revin mentioned before, we also wanted to keep Queued as light as possible; because of this, we decided early on to not use any of the Dijit infrastructure to create the queue listings. Not only that, but the Dojo Grid would not work for the queues because it doesn’t support drag and drop reordering of rows. This meant we would have to come up with something which would be flexible (yet fast) to render the queue.

In the user interface design phase, we decided that each of the lists in the “Your Queue” section would be based on HTML tables. In Queued, only the DVD queue and the Instant list can be reordered, so we’ll focus on the DVD queue.

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In Part I of Queued and AIR issues, I talked about some of the challenges we faced during the development of Queued, our AIR application that allows you to manage your Netflix queues. In this post, I’ll discuss five other issues we ran across.

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Dojo is a very flexible toolkit; it doesn’t dictate how you organize your code or create your widgets. It simply provides tools, and it’s up to you to decide how you want to fit them together. Developing with AIR puts you squarely in the browser-based application model, but aside from that it mostly stays out of your way as well. As part of our series on the Queued development process, I’m going to take a look at the decisions we made and the philosophies we adopted for the project. It should provide some insight into our process.

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The latest addition in the Dojo 1.3 release is the new dojox.charting class, DataChart. Its primary purpose is to make connecting a chart to a Data Store a simple process. There are also other benefits with DataChart: less parameters are needed to create a basic chart, and more defaults and convenience methods get you up and running quickly with Dojox Charting.

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Last month, we announced Queued, an open-source application for managing your Netflix Queue. Queued is a desktop application created with web technologies and techniques including the Dojo Toolkit, and it is distributed as an Adobe AIR application to provide several performance boosting benefits from living on the desktop.

At SitePen, we help our clients build great web applications. Most are not available for public consumption as they live behind company firewalls and/or require licensing. On the other hand, Queued is free and open-source software, BSD-licensed, and hosted on Google Code.

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New to Dojo 1.2+ is dojox.html.style. This is a collection of methods which give you the ability to query the stylesheets collection in a document, add and remove rules, and dynamically create new sheets. In this article I’ll explain why and where this is of use, and walk through a split-panel demo that uses dynamic stylesheets to size a 2 column layout.

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Dojo is big, but it’s not unwieldy. You don’t have to learn it all to be productive. There are probably large pieces of the toolkit that you’ll never even need, but Dojo is built so that if you don’t need something, it doesn’t weigh you down. Where it counts, Dojo is actually quite lean. In the most basic unit of the toolkit—dojo.js itself—you’ll find enough power to get real work done. It’s worth looking at what you buy when you spend 26KB (gzipped) on JavaScript code rather than a pretty PNG. I think you’ll like what you find.

Let’s start with event handling. I’ll cover the basic techniques first, then finish with a real-world implementation of the concept by looking at Queued, our AIR-based Netflix queue manager.

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The module dojox.rpc.Client was introduced in Dojo Toolkit version 1.2, providing extra request headers on XMLHttpRequests to facilitate implementing deterministic request handling on servers. Browsers typically use two or more TCP connections to send HTTP requests to a server, while subsequent requests are often routed on separate TCP connections. This means there is no guarantee that the request that is sent first will arrive at the server first. With sophisticated web applications, non-determinism can lead to bugs that are very difficult to track down.

If a web application sends multiple requests to a server and assumes that the server will handle them in the order they were sent, this non-determinism can be problematic. Furthermore, messages that arrive out of order can be rare, and therefore problems can be hard to reproduce. On old modem connections, packets were sequenced over a slow PPP connection that made out of order messages almost non-existent. With modern broadband connections, the race becomes more interesting. HTTP pipelining adds another mechanism that can lead to messages arriving out of order and with browsers beginning to support and use pipelining, messages arriving out of order will become even more likely in the future.

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Dijit has a tremendous wealth of high quality and feature-rich form elements providing key functionality including validation, time calculation, spinner controls, calendars, and much more. Furthermore, Dijit gives you a set of themes to choose from: Tundra, Soria, Noir, and Nihilo.

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