Professional Ajax, 2nd Edition

2.2. Ajax Communication Techniques

Now that you understand the basics of how HTTP communication works, it's time to look into enacting such communication from within a web page. As you know, there are a lot of requests going back and forth between the browser and server while you are surfing the Web. Initially, all these requests happened because the user made an overt action that required such a step. Ajax techniques free developers from waiting for the user to make such an action, allowing you to create a call to the server at any time.

As discussed in Chapter 1, Ajax communication supports a number of different techniques. Each of these techniques has advantages and disadvantages, so it's important to understand which one to use in which situation.

2.2.1. The Hidden Frame Technique

With the introduction of HTML frames, the hidden frame technique was born. The basic idea behind this technique is to create a frameset that has a hidden frame that is used for client-server communication. You can hide a frame by setting its width or height to 0 pixels, effectively removing it from the display. Although some early browsers (such as Netscape 4) couldn't fully hide frames, often leaving thick borders, this technique still gained popularity among developers.

2.2.1.1. The Pattern

The hidden frame technique follows a very specific, four-step pattern (see Figure 2-1). The first step always begins with the visible frame, where the user is interacting with a web page. Naturally, the user ...