PHP jQuery Cookbook: jQuery and PHP are the dynamic duo that will allow you to build powerful web applications. This Cookbook is the easy way in with over 60 recipes covering everything from the basics to creating plugins and integrating databases.

You surely know how typical web applications work. You enter a URL in your browser and the browser loads that page for you. If you are required to submit a form, you will fill it and the browser sends the filled data to the server side for processing. During this time you wait for the entire page to load. If you are on a slow connection, the wait is even longer.

Let me describe another typical scenario, a web page has two select boxes. The first select box asks you to select the name of a country. You make your selection and the whole page loads to populate the second select box with the names of the cities in that country. If by mistake you made a wrong selection, fixing your mistake means another page load. Irritating isn't it?

The point I am trying to make here is: why load the complete page every time? Why can't you just select the country name and using some magic in the background be provided with the city list without loading the complete page? Maybe you can fill some other...

This recipe will teach you the usage of jQuery's get method to retrieve data from a PHP script. We will see a simple example where data will be fetched from the server using the get method based on user selection from a form.

After going through this recipe you will be able to distinguish between AJAX requests and simple HTTP requests in your PHP code.

GET and POST are the two most frequently used methods for accessing pages. In the first recipe you learned to make requests using GET method.

This recipe will make use of jQuery's $.post() method to retrieve data from a PHP script. We will see a simple example where we will fill some data in a form and the data will be sent to PHP using the POST method. Sent data will be processed by PHP and then displayed in the browser.

Consider a case where a user is allowed to select a date on a page and an AJAX request is made to the server to fetch some data against that date. If the request is under processing and in the meantime the user selects another date and a new request is sent, the server now has two requests pending.

Imagine what will happen to an application if there are multiple users repeating the same behavior. Desirable behavior in this case will be to cancel the pending request and allow only the current one.

This recipe will explain how to cancel any pending requests.

The larger a web page the more time a browser will take to download it. This may degrade the user experience in case of slow connections or larger pages.

One approach that can be followed is to load only what is absolutely necessary for the user and load the rest of the content when required. There are some sections on a page which are rarely accessed. It will make page loads faster and user experience will improve.

In this recipe we will demonstrate this case with a simple example. We will create a single HTML page and will allow the user to load its one section when required.

Errors are inevitable. Period. Sometimes things are not in your control—like server failures—and in this case you must have an error handling mechanism in place, which can catch the errors and show them to the users. Throughout the recipes in this chapter we have implemented callback functions that execute when a request is successful. It may happen (and I promise you it will happen) that you typed a filename incorrectly or the server encounters an error and you get an error rather than a successful response.

This recipe will explain how to deal with such situations in AJAX requests.

In case of GET requests, browsers cache these requests and when the request is invoked again they do not send the request to the server and instead serve it from the cache.

This recipe will explain how to force browsers to send the request to a server instead of serving it from the cache.

Think of a rich Internet application that makes heavy use of JavaScript to interact with the user. Such a page typically consists of more than one JavaScript files, such as a file for calendar control, another file for special effects, yet another plugin for your cool accordion, and so on.

This results in the increase of the page load time as browsers cannot download all of these files simultaneously. The best solution for this is to load only absolutely necessary files at the time of loading the page and load the other files when required.

This recipe will explain how JavaScript files can be loaded on demand.