When you go to the jQuery Web site to download jQuery files, you’ll find that you have two file options, shown in Figure 1: a production version (compressed) and a development version (uncompressed) of the core jQuery library. The files sizes for version 1.5 are quite different: 29KB and 207KB.
Figure 1. The download panel on the jquery website.
TIP: You can download older versions of jQuery using the Download link on the jquery.com Web site (not shown in Figure 1) as well as plugins and other extensions.
Figure 2. The development version of the jQuery library file.
Then, when you’re ready to deploy your site, use the 29KB production version in the file named jquery-1.5.min.js, where “min” stands for minified. This file has had all of the unnecessary whitespace removed, variable names shortened, and other compression tricks applied to get the size of the file as small as possible. As you can see in Figure 3, the file consists of the readable comments at the top of the file, and a single line of code; you’ll see that line is 83,996 characters long if you scroll all the way to the right. If you scroll through the one line of code, you’ll find that it is almost impossible to follow the logic. We humans just weren’t built to process such condensed data! But a browser knows just what to do with it.
Figure 3. The production version of the jQuery library file.
The benefit of the production version is that users have to download a much smaller file when they load your page, and you save a bit on your bandwidth bill. Even though the browser will cache the file for subsequent page views, this will mean that the initial page load will be noticeably faster, particularly over slower connections.
TIP: You can get the size of the development version even smaller if you use gzip compression in your Web site.