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ColdFusion: Article

When AJAX Happens to Old Browsers

Building a single application that supports both new and old browsers

One of the latest crazes in Web development is AJAX. Unless you've been living in a cave for the last year, you've heard of this old, yet currently popular, technique for making HTTP requests to a server without refreshing the Web page. While claims of smaller bandwidth, faster response, and highly interactive user interfaces may intrigue you, one must ask, "Will it work for my user base?"

We've seen this same issue before. It's not an AJAX-specific issue; rather, it's a JavaScript issue. There are users that either by choice or mandate are stuck with an ancient Web browser. There are others who still don't have JavaScript enabled on their browsers. It's difficult to know exactly how many people don't have JavaScript turned on, but estimates range from 5%-10%.

Is 5%-10% a significant user population? It depends on who you ask. Some businesses can take a chance of alienating this user base at the prospect of wowing the remaining 90%, while for others, it's either necessary or desirable to accommodate all users. It seems that you may be left with only two options when deciding whether to implement AJAX on your site:

  • Leave the users of older browsers behind.
  • Accommodate this small user base at the expense of lesser functionality for the remaining 90%.
I'd like to propose a third option:
  • Accommodate both groups through effective planning and design.
"Accommodate both groups," you ask. "Doesn't that mean that I need to develop two separate Web applications?" With careful planning and design, you can develop a single application that provides essential functionality to all users, while providing enhanced functionality to those whose browsers can handle it.

"Essential" versus "Enhanced" Functionality
Essential functionality means providing a user with the ability to complete a task or use a service. For instance, suppose one of the services on your Web site is a weekly newsletter. To subscribe to the newsletter, a user must complete a registration form. What happens when the user clicks the submit button at the end of the form? Few things are more frustrating than completing a large form only to have the submit button "shoot blanks" because it requires JavaScript to function. Essential functionality dictates that the submit button works regardless of whether the user is using Firefox, Internet Explorer, Safari, Lynx, or a screen reader.

Enhanced functionality means adding all of the bells and whistles that really set your application apart. While such features aren't essential, adding them to an application usually provides faster ways to accomplish tasks or easier ways of doing things. Enhanced functionality includes such things as:

  • client-side form validation
  • dynamic HTML effects
  • AJAX
The strategy that I suggest for accommodating both essential and enhanced functionality is to add "bells and whistles" to a basic application. That is, we'll create an application that satisfies the essential functionality and then provide a way for enhanced functionality to be attached to the application only if the client's browser will support it.

The Sample Application: A Contact Manager
The sample application accompanying this article is a simple contact manager (see Figure 1). The goal of this application is to provide users with the ability to:

  • Add new contacts
  • Edit existing contacts
  • View all contacts
  • Delete contacts
First we'll build the application that addresses essential functionality. In the basic application, all GET and POST operations will be full-page refreshes. Later, we will add some AJAX functionality to the application. To keep the example simple, it stores all contacts in a query object in the application scope.

Coding the Basic Application
The basic application is in the /ajax/no-js/ directory of the code samples. One of the first things that I did when building the basic application was to separate queries, content sections, and controlling logic into separate templates. This is something that can be done now to prepare the application to work for both basic and advanced browsers. AJAX calls and other dynamic effects often need small segments of content, or data in XML, rather than HTML. Instead of duplicating code, we write each query and display template and include them in potentially multiple places.

Most of the business logic, or model layer, is in contactManager.cfc. It contains all of the operations needed to read and manipulate contacts. The contact listing table, contact entry and edit form, and delete confirmation page are all in separate templates. layout.cfm is a custom tag that contains the basic HTML skeleton to wrap the other content sections. Finally, index.cfm handles all of the possible actions from the browser in a <cfswitch> tag. Most of the action handlers look like the following saveRecord case:

<cfcase value="saveRecord">
<!---put the contact information in a struct --->
<cfinvoke returnvariable="contact" component="#request.manager#"
method="populateContact" argumentcollection="#form#"/>
<!--- store the contact in the database --->
<cfset request.manager.saveContact(contact)/>
<!--- retrieve an updated list of contacts --->
<cfset qContactListing = request.manager.getAll()/>
<!--- create an empty contact for the entry form --->
<cfset contact = request.manager.populateContact()/>
<cf_layout title="Contact Manager" message="Contact was successfully
<cfinclude template="dspListing.cfm"/>
<cfinclude template="dspEntryForm.cfm"/>

Each action handler case calls the business methods and includes the templates necessary to perform the action.

Finally, I made sure that the markup was clean and simple, and that all visual styling was placed in a stylesheet. Clean markup provides three benefits, regardless of whether the application will be using AJAX:

  1. It's easier to work with the HTML structure using JavaScript DOM APIs. and stylesheets.
  2. It usually means less data is sent back to the client at one time, since unnecessary elements and attributes are eliminated. When we send HTML segments to the client using AJAX, those responses will be even smaller.
  3. The HTML is often easier to read and maintain.
Try out the sample application so you understand how it works. At this point, the basic application works reliably and provides essential functionality. Because, it's not very exciting, it's time to add some enhanced functionality.

Grafting In the Enhancements
The enhanced application is in the /ajax/with-js/ directory of the code samples. In this version of the application, we're going to add some AJAX calls. This means replacing any of the pages exit points - the edit links, delete links, and save button - with JavaScript calls to actions in the ColdFusion application. A common way to do this is to make the necessary onclick event handler an attribute on the anchor tag or submit button like so:

<a href="index.cfm?action=editRecord...." onClick="lookupContact();">edit</a>

Rather than cluttering up the HTML with event handlers, I prefer to attach them to the elements using JavaScript calls in the header. The calls are usually invoked as part of the browser window's onload event. This keeps the HTML content and JavaScript code clearly separated. To make it easy to attach events using this method, let's make two quick changes to the code:

  1. Add class attributes to the edit and delete links, and an id attribute to the submit button. This will make it easier to find the elements using JavaScript.
  2. Move the HTML contact table to a separate template (dspListingContent.cfm) and include it in the original template using <cfinclude/>. The HTML table is a key page fragment that we'll want to return to the client using AJAX.

More Stories By Jeremy Lund

Jeremy Lund is the manager of the Web Resource Center at University Health Care in Salt Lake City, Utah (http://uuhsc.utah.edu/wrc/). As the manager he coordinates development efforts, designs their Web architecture, and, in the time left, develops Web applications. He has worked with Internet technologies for over seven years, and enjoys working not only with ColdFusion, Java, and Perl, but is also an advocate of using XHTML and CSS. Jeremy received a bachelor's degree in computer engineering from the University of Utah, and is a Sun Certified Programmer for the Java 2 platform.

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AJAXWorld News Desk 06/20/06 04:07:08 PM EDT

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