Welcome!

Eclipse Authors: Pat Romanski, Elizabeth White, Liz McMillan, David H Deans, JP Morgenthal

Related Topics: Java IoT, Machine Learning

Java IoT: Article

Developing Intelligent Web Applications With AJAX (Part 2)

A peek into modern technologies for browser-based applications

The publicity that AJAX grabbed over the last half a year is based on closing the gap between the Web applications and the desktop applications, combining the "reach" and "rich." At the same time, the gap between the technological level of AJAX and what corporate developers expect in their modern arsenal is really astonishing. After all, AJAX is neither a tool nor a platform. There is no AJAX standards committee or community process in place. While software vendors are crafting proprietary development platforms on top of AJAX (which pretty much means "from scratch"), early adopters of AJAX are left on their own.

In Part 1 (JDJ, Vol. 10, issue 9) we touched on the foundation of AJAX - the ability to establish script-to-server communication. This is what makes HTML pages dynamic and responsive. Does it mean we are ready to kick-off our own version of Yahoo mail? No, we are not. Here is why: AJAX is a mixed blessing. On one hand it enables us to create rich, desktop-class applications on the Web. On the other, if we compare "page-flipping" Web applications with the client/server or Swing ones, the development practices are not quite the same. What about management expectations? We'll need to get used to the fact that it takes time to build a rich UI. The more flexibility with more permutations the user is allowed - the more time it takes.

The answer, of course, is component libraries, frameworks, and industrial-strength tools. Leaving tools aside, this article concentrates on what is available for AJAX enthusiasts today. Addressing a need to build reusable business components, it focuses on the "hidden" object-oriented power of JavaScript. Also, by addressing a need to build custom-rich UI components, it illustrates a convenient way to encapsulate presentation logic in custom client-side HTML tags.

AJAX Language: Object-Oriented JavaScript
By definition, JavaScript is the language of classic AJAX. Unlike Java, JavaScript does not enforce the OO style of coding. That said, it's surprising how often it's overlooked that Java-Script fully supports all the major attributes of an OO language: inheritance, polymorphism, and encapsulation. Douglas Crockford even named Java Script "The World's Most Misunderstood Programming Language." Let's review the object-oriented side of JavaScript.

Data Types
In Java, a class defines a combination of data and its associated behaviors. While JavaScript reserves the class keyword, it does not support the same semantic as in conventional OOP languages.

It may sound strange but in JavaScript, functions are used as object definitions. By defining a function in the example below you, in fact, define a simple empty class - Calculator:

function Calculator() {}

A new instance is created the same way as in Java - by using the new operator:

var myCalculator = new Calculator();

The function not only defines a class, but also acts as a constructor. The operator new does the magic, instantiating an object of class Calculator and returning an object reference in contrast to merely calling the function.

Creating an empty class is nice but not really useful in real life. We are going to fill-in the class definition using a Java-Script prototype construct. JavaScript uses prototype to serve as a template for object creation. All prototype properties and methods are copied by reference into each object of a class, so they all have the same values. You can change the value of a prototype property in one object, and the new value overrides the default, copied from the prototype, but only in that one instance. The following statement will add a new property to the prototype of the Calculator object:

Calculator.prototype._prop = 0;

Since JavaScript does not provide a way to syntactically denote a class definition, we'll use the with statement to mark the class definition boundaries. This will also make the example code smaller as the with statement is allowed to perform a series of statements on a specified object without qualifying the attributes.

function Calculator() {};
with (Calculator) {
   prototype._prop = 0;
   prototype.setProp = function(p) {_prop = p};
   prototype.getProp = function() {return _prop};
}

So far we have defined and initialized the public _prop variable as well as provided getter and setter methods for it.

Need to define a static variable? Just think of the static variable as being a variable owned by the class. Because classes in JavaScript are represented by function objects, we just need to add a new property to the function:

Calculator.iCount = 0;

Now that the iCount variable is a property of the Calculator object, it will be shared between all instances of the class calculator.

function Calculator() {Calculator.iCount++;};

The above code will count all created instances of the class Calculator.

Encapsulation
Using "Calculator", as defined above, permits access to all the "class" data, increasing the risk of name collisions in inherited classes. We clearly need encapsulation to view objects as self-contained entities.

A standard language mechanism of data encapsulation is private variables. And a common JavaScript technique for emulating a private variable is to define a local variable in the constructor, so that this local variable is accessible exclusively via getter and setter - inner functions of the very same constructor. In the following example, the _prop variable is defined within the Calculator function and is not visible outside of the function scope. Two anonymous inner functions, assigned to setProp and getProp attributes, provide access to our "private" variable. Also, please note the use of this, quite similar to how it is used in Java:

function Calculator() {
   var _prop = 0;
   this.setProp = function (p){_prop = p};
   this.getProp = function() {return _prop};
};

What is often overlooked is the cost of such encapsulation in JavaScript. It can be tremendous, because inner function objects get repeatedly created for each instance of the "class".

Accordingly, since constructing objects based on the prototype is faster and consumes less memory, we cast our vote in favor of public variables wherever performance is critical. You can use naming conventions to avoid name collisions, for example, by prefixing public variables with the class name.

Inheritance
At first glance, JavaScript lacks support for the class hierarchy similar to what programmers of conventional object-oriented languages expect from the modern language. However, although JavaScript syntax does not support class inheritance as in Java, inheritance can still be implemented by copying an instance of a previously defined class into the prototype of the derived one.

Before we provide an illustration, we need to introduce a constructor property. JavaScript makes sure that every prototype contains constructor, which holds a reference to the constructor function. In other words, Calculator.prototype.constructor contains a reference to Calculator().

More Stories By Victor Rasputnis

Dr. Victor Rasputnis is a Managing Principal of Farata Systems. He's responsible for providing architectural design, implementation management and mentoring to companies migrating to XML Internet technologies. He holds a PhD in computer science from the Moscow Institute of Robotics. You can reach him at [email protected]

More Stories By Anatole Tartakovsky

Anatole Tartakovsky is a Managing Principal of Farata Systems. He's responsible for creation of frameworks and reusable components. Anatole authored number of books and articles on AJAX, XML, Internet and client-server technologies. He holds an MS in mathematics. You can reach him at [email protected]

More Stories By Igor Nys

Igor Nys is a Director of Technology Solutions at EPAM Systems, Inc, a company combining IT consulting expertise with advanced onshore-offshore software development practices. Igor has been working on many different computer platforms and languages including Java, C++, PowerBuilder, Lisp, Assembler since the mid 80's. Igor is currently managing a number of large distributed projects between US and Europe. In addition Igor is the author of the award-winning freeware system-management tools, and he was closely involved in the development of XMLSP technology - one of the AJAX pioneers.

Comments (2) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
David 11/29/05 01:24:43 PM EST

This looks like the true bleeding edge, once again creating more headaches in the write many, test many world that web services were supposed to have resolved.

What good is AJAX of this sort when there are differences between just two browsers? Do we really need more technology that is non-standard to the point where we'll need lots of adaptations just to handle the various types of browsers people will use? No doubt this will also mean variations will be needed even among differing versions of the same browser class.

Without a standard set of markup and scripting elements, AJAX is just going to make more bad web sites that work with only one browser but fail with others.

Edwin 11/25/05 03:06:50 PM EST

Software AG sells the Ajax based RIA developement environment CAI COmposite Application Integrator. This product is on the market for several years now. So saying there are no RAD Ajax tools available...

IoT & Smart Cities Stories
The challenges of aggregating data from consumer-oriented devices, such as wearable technologies and smart thermostats, are fairly well-understood. However, there are a new set of challenges for IoT devices that generate megabytes or gigabytes of data per second. Certainly, the infrastructure will have to change, as those volumes of data will likely overwhelm the available bandwidth for aggregating the data into a central repository. Ochandarena discusses a whole new way to think about your next...
DXWorldEXPO LLC announced today that Big Data Federation to Exhibit at the 22nd International CloudEXPO, colocated with DevOpsSUMMIT and DXWorldEXPO, November 12-13, 2018 in New York City. Big Data Federation, Inc. develops and applies artificial intelligence to predict financial and economic events that matter. The company uncovers patterns and precise drivers of performance and outcomes with the aid of machine-learning algorithms, big data, and fundamental analysis. Their products are deployed...
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...
All in Mobile is a place where we continually maximize their impact by fostering understanding, empathy, insights, creativity and joy. They believe that a truly useful and desirable mobile app doesn't need the brightest idea or the most advanced technology. A great product begins with understanding people. It's easy to think that customers will love your app, but can you justify it? They make sure your final app is something that users truly want and need. The only way to do this is by ...
CloudEXPO | DevOpsSUMMIT | DXWorldEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
Cell networks have the advantage of long-range communications, reaching an estimated 90% of the world. But cell networks such as 2G, 3G and LTE consume lots of power and were designed for connecting people. They are not optimized for low- or battery-powered devices or for IoT applications with infrequently transmitted data. Cell IoT modules that support narrow-band IoT and 4G cell networks will enable cell connectivity, device management, and app enablement for low-power wide-area network IoT. B...
The hierarchical architecture that distributes "compute" within the network specially at the edge can enable new services by harnessing emerging technologies. But Edge-Compute comes at increased cost that needs to be managed and potentially augmented by creative architecture solutions as there will always a catching-up with the capacity demands. Processing power in smartphones has enhanced YoY and there is increasingly spare compute capacity that can be potentially pooled. Uber has successfully ...
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things'). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing. IoT is not about the devices, its about the data consumed and generated. The devices are tools, mechanisms, conduits. This paper discusses the considerations when dealing with the...