Welcome!

You will be redirected in 30 seconds or close now.

ColdFusion Authors: Yakov Fain, Jeremy Geelan, Maureen O'Gara, Nancy Y. Nee, Tad Anderson

Related Topics: ColdFusion, Machine Learning

ColdFusion: Article

AJAX Custom Error Handling: Enhancing the Interactive User Experience

AJAX and Rich Internet Applications

AJAX has become an increasingly popular tool to develop RIAs. With AJAX, as with many new technologies, developers often overlook core application issues such as error handling. While many current AJAX frameworks come with ways to handle errors, the built-in error-handling methods might not be quite what you need, and it's possible that you might not even want to adopt a specific AJAX framework at all. So how do you handle errors in AJAX?

This article will guide you through one possible way to implement custom error handling in AJAX using many of the same techniques that you'll likely read about in other parts of this magazine. Because AJAX represents a big paradigm shift in the way users interact with Web applications, it's easy to leave your users confused when things don't quite work as they'd expected. To enhance the user experience, it's equally important to alert them when something goes exactly as planned and enhances the interactive experience.

Consider for a moment a hypothetical AJAX application that updates employee information. Users will fill out fields and click on a "Save" button to process the update. In a traditional Web application the user expects to wait a moment while the server updates the record then anticipates another page that displays a confirmation message. This is the typical request/return scenario that our Internet conditioning forces us to accept.

Now let's look at the same example using AJAX techniques. The end user still fills out form fields and clicks on the "Save" button but instead of seeing the confirmation message, nothing seems to happen. This can leave the user confused and unsure that his information was saved, yet with AJAX, the database update occurred exactly as expected. Here's how you can implement a messaging and error system in a simple employee information maintenance application that will alert a user as records are updated.

Process at a Glance
The process isn't much different from any typical AJAX request/response. A request is created, sent to the server, checked for error conditions, XML is sent back to your request page, and checked in the browser for a status message, which is displayed, if it exists.

Create an Area to Display Status Messages
We'll begin to create our code by creating our CSS format classes for our status messages. Let's create three styles for our application's potential conditions: error, success, and hidden, which correspond to the two cardinal states (error and success) of our query (hidden being used when no update is currently active):

.error{
     font-family: Arial, Helvetica, sans-serif;
     font-size: 10px;
     font-weight: bold;
     color: #FFFFFF;
     background-color: #FF0000;
     display:block;
}
.success {
     font-family: Arial, Helvetica, sans-serif;
     font-size: 10px;
     font-weight: bold;
     color: #FFFFFF;
     background-color: #009900;
     display:block;
}
.hidden {
     display:none;
}

Once we have our styles set, we have to put them to use. We'll do this by creating an area in our application to display the status messages returned by the server. This display area can be any type of HTML container such as table, div, or span; we'll use a div. Once the container is created, we'll set the initial style to hidden, as follows:

<div id="message" name="message" class="hidden"></div>

Creating the ColdFusion Page To Process the Request.
At this point, you'll find that the code you've created doesn't do much - you have three CSS styles, one of which is called by your container div, but its class is set to not display on the rendered page. To create conditions where an error or success message might actually exist, we'll look at a ColdFusion template that updates an employee's database record. Since the focus of this article is on error handling we'll skip the details of updating the record and get right to the process of building the XML that returns our status message.

First let's look at an example of processing an update of one of our employee records. Since this is a situation where no data is being returned (because we're not using a SELECT statement), we really only need to deliver either a success or error message to our user.

To do this, we'll have to create a variable to hold the XML string then add the XML declaration to it:

<cfset xml = "<?xml version=""1.0"" encoding=""UTF-8"" standalone=""yes"" ?>">

Now that we've created our variable, "xml," we're going to want to do some simple data validation - in this case, to make sure that a valid department ID was passed into the template. If the department ID passed in is not valid, we're going to want to set the first node of the XML document to (<error>), add the error message, and close the error node (</error>). For our purposes, we'll assume that a "departmentID" value of 0 or of a non-numeric value constitutes an invalid condition. We're also going to include "try/catch" conditions to cover database errors and general failures:

<cfif departmentId eq 0 OR NOT IsNumeric(departmentId)>
<cfset xml = xml & "<error>Invalid department specified.</error>">
<cfelse>
     <cftry>
<cfcatch type="database">
     <cfset xml = "<?xml version=""1.0"" encoding=""UTF-8"" standalone=""yes"" ?>
<error>There was a error communicating with the server, please call the help desk at
x555.</error>">
</cfcatch>
<cfcatch type="Any">
<cfset xml = "<?xml version=""1.0"" encoding=""UTF-8"" standalone=""yes"" ?>
<error>There was a error processing your request. Please try again later or call the help
desk at x555.</error>">
</cfcatch>
</cftry>
</cfif>

One thing to note here is that the entire XML string is overwritten in the catch statement. This eliminates a situation caused by an error being thrown in the middle of building the XML string. Specifically this condition sends an incomplete and unpredictable XML document back to the requesting page.Let's walk through an example of a successful and unsuccessful update of an employee record. The main screen of the employee update application is shown in Figure 1. For this example let's say that a phone extension can only be used once per employee in a company. When a user clicks on the "Update Employee" link the main screen will prepare the AJAX request and send it to a ColdFusion template. The template will then process the update and send a XML message back to the main screen.

More Stories By Ryan Anklam

Ryan Anklam is the Chief Information Officer at Innova Creative Media, Inc. His current focus is on using ColdFusion to develop large scale hosted applications. Ryan has been developing ColdFusion applications since 1996. In addition, he is also a Microsoft Certified Professional with demonstrated skills in C# and SQL Server.

Comments (6) 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
Kim 03/20/06 03:07:22 PM EST

On page two, it reads Creating JavaScript to Handle the Errors
Let's take a look at what we've done so far: we've created our CSS style classes, we've created our display container, we have our query, our template to update the employee record, and created our error-handling logic.

I don't see where we created the query or the template to update the employee record so far in the article.

Dave 03/20/06 12:34:38 PM EST

Unfortunately the links to the demo and zip file are not working for this article. Is there another place one can test this out and download the source?

Thanks,
Dave

SYS-CON India News Desk 03/19/06 10:31:11 AM EST

AJAX has become an increasingly popular tool to develop RIAs. With AJAX, as with many new technologies, developers often overlook core application issues such as error handling. While many current AJAX frameworks come with ways to handle errors, the built-in error-handling methods might not be quite what you need, and it's possible that you might not even want to adopt a specific AJAX framework at all. So how do you handle errors in AJAX?

SYS-CON Italy News Desk 03/19/06 09:50:32 AM EST

AJAX has become an increasingly popular tool to develop RIAs. With AJAX, as with many new technologies, developers often overlook core application issues such as error handling. While many current AJAX frameworks come with ways to handle errors, the built-in error-handling methods might not be quite what you need, and it's possible that you might not even want to adopt a specific AJAX framework at all. So how do you handle errors in AJAX?

Dev 03/19/06 08:30:53 AM EST

The URL for download the source cannot be reached. Is there any other way to get the source ?

Dev 03/19/06 08:30:43 AM EST

The URL for download the source cannot be reached. Is there any other way to get the source ?

IoT & Smart Cities Stories
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.
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...
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 ...
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 ...
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...
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...
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...