Ajax Application Design

Asynchronous is the operative word with Ajax, and here's what it's all about.
Conclusion

This month, we finally produced an application worthy of the Ajax moniker. We used a combination of JavaScript (on the client side) and Perl (on the server side) to check whether a user name was already taken. In doing so, we saw how to use the POST method for submitting data and sent a named parameter to the server. In making these changes, we turned a simple, insecure and unscalable program into a relatively secure and scalable one, without sacrificing the immediate response and interactivity that Ajax brings to the table.

At the same time, you might have noticed our HTML page contained a large number of functions that will be useful for a wide variety of Ajax applications. Starting next month, we will look at some of the open-source libraries that make it easier to create Ajax applications, allowing you to concentrate on the higher-level details.

Reuven M. Lerner, a longtime Web/database consultant, is a PhD candidate in Learning Sciences at Northwestern University in Evanston, Illinois. He currently lives with his wife and three children in Skokie, Illinois. You can read his Weblog at altneuland.lerner.co.il.

______________________

Comments

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Good article

gds's picture

Really good articles on ajax fundamentals. One comment I have is that it is not pointed out in Part 2 and 3 that the database access, register.pl, is still in effect. It is also easy to change check-name-exists.pl above to use similar database methods as register.pl users:


#!/usr/bin/perl
use strict;
use diagnostics;
use warnings;
use CGI;
use CGI::Carp;
use DBI;
# ------------------------------------------------------------
# # Connect to the database
# ------------------------------------------------------------
my $dbname = 'test';
my $dbuser = 'gene';
my $dbpassword = '';
my $dbh = DBI->connect("DBI:mysql:dbname=$dbname",
$dbuser, $dbpassword,
{
AutoCommit => 1, RaiseError => 1,
PrintError => 1, ChopBlanks => 1}) ||
print "Error connecting: '$DBI::errstr' ";

# Define the usernames that are taken
# (Use a hash for lookup efficiency)
#my %usernames = ('abc' => 1,
# 'def' => 1,
# 'ghi' => 1,
# 'jkl' => 1);
# ------------------------------------------------------------
my $query = new CGI;
print $query->header("text/plain");
# Get the POST data
my $postdata = $query->param("POSTDATA");
# Get the username
my ($name, $value) = split /=/, $postdata;
my $username = '';
if ($name eq 'username')
{
$username = $value;
}
my $select_sql = "SELECT COUNT(*) FROM Users WHERE username = ?";
my $select_sth = $dbh->prepare($select_sql);
$select_sth->execute($username);
my ($username_is_taken) = $select_sth->fetchrow_array();

# If this username is defined, say "yes"!
if ($username_is_taken)
{
print "yes";
}
# Otherwise, say "no"!
else
{
print "no";
}

I also change it to use onblur instead of onchange but had to pass a parameter to checkUserName():


function checkUsername(val) {
:
var username = val; //document.forms[0].username.value;
xhr.send("username=" + escape(username));

White Paper
Linux Management with Red Hat Satellite: Measuring Business Impact and ROI

Linux has become a key foundation for supporting today's rapidly growing IT environments. Linux is being used to deploy business applications and databases, trading on its reputation as a low-cost operating environment. For many IT organizations, Linux is a mainstay for deploying Web servers and has evolved from handling basic file, print, and utility workloads to running mission-critical applications and databases, physically, virtually, and in the cloud. As Linux grows in importance in terms of value to the business, managing Linux environments to high standards of service quality — availability, security, and performance — becomes an essential requirement for business success.

Learn More

Sponsored by Red Hat

White Paper
Private PaaS for the Agile Enterprise

If you already use virtualized infrastructure, you are well on your way to leveraging the power of the cloud. Virtualization offers the promise of limitless resources, but how do you manage that scalability when your DevOps team doesn’t scale? In today’s hypercompetitive markets, fast results can make a difference between leading the pack vs. obsolescence. Organizations need more benefits from cloud computing than just raw resources. They need agility, flexibility, convenience, ROI, and control.

Stackato private Platform-as-a-Service technology from ActiveState extends your private cloud infrastructure by creating a private PaaS to provide on-demand availability, flexibility, control, and ultimately, faster time-to-market for your enterprise.

Learn More

Sponsored by ActiveState