Chapter 6. Web Remoting

NOW THAT WE'VE SEEN HOW AJAX APPS CAN MANIPULATE THE DISPLAY, IT WOULD BE USEFUL IF THEY could use that capability to show data arriving from the server. We'd also like to accept input and upload it to the server. The Web Remoting patterns let JavaScript directly issue calls to the server. The point is to let the browser make a query or upload some data, without actually refreshing the page.

The first pattern is Web Service, which explains how the server side exposes functionality to be accessed by the browser.

The remaining patterns are the most useful and most common mechanisms for web remoting.^[*] XMLHttpRequest Call is a clean way for the browser script to invoke and catch responses from the server. IFrame Call provides a similar use by exploiting IFrame functionality. HTTP Streaming, also known as "Push" (or "Comet"), allows the server to continue streaming new data down the pipe, without the browser having to issue new requests. On-Demand JavaScript is a fairly broad-scoped pattern and is included in this section because one style, Script Tag Generation, is a distinctive technology that's becoming a popular way to directly access external domains.

^[*] Other techniques do exist, and are mentioned in "Alternatives" in XMLHttpRequest Call later in this chapter.

Of the four techniques, XMLHttpRequest Call is the cleanest, because XMLHttpRequest is specifically designed for web remoting. Nevertheless, all of the techniques are effective, and each has a certain set of situations where it's the superior choice. See the "Alternatives" section for XMLHttpRequest Call for a comparison of the various techniques.