This JSP taglib dynamicaly minifies, combines, gzippes, sets various headers, takes care of browser-caching issues (like changing the URL when the file has changed), recognizes changes in the files, and more for JavaScript and CSS.

And it’s easy to use:

Take a look into the guide.

There are various supported compression algorithems that are available out-of-the-box, like YUI Compressor, JSMin, ..

@heatdphondotes: You should include all (or some combination) of scripts using one script tag as opposed to separate script tags. Also, consider different ways of combining files taking into consideration browser caching, shared versus unshared files across pages, scripts at the bottom performance rule, etc.

@Patay/Eric: I addressed this concern under the Combo Handler Best Practices section: “By combining everything into one large file and using this file across your entire site, some pages will spend time downloading more than it really needs. Instead, take a look at different types of combinations.” Also, keep in mind that not all users will visit your site with a primed cache: Performance Research Part 2

@Luke: I probably should have added an image component at the end of both figures to illustrate when the pages finish loading. You’re correct in that there would still be a gap between the combined script and image in figure 2 for the time the browser takes to parse and render. However, the overall response time is still typically faster when using a combined file versus six separate files.

The gaps between the scripts indicate the time the browser takes to parse and render each script.

Isn’t the figure 1 slightly misleading in that the browser will block during parsing and rendering. Therefore, the real browser “response” will occur afterwards this completes. Presumably, the parse/render time of the combined script would be equal to the sum of the parse/render time for each individual script. Thus, the combined file would have a large “gap” after downloading until the parse/render completes.

Also, how does downloading 1 file compare to the benefits of achieving parallelization of downloading 2?

Each of this combination will be cached at browser as different file, because for browser each combo is a different script file.

I was also thinking the same thing. I know it used to be stated that one of the benefits of using the Yahoo CDN was that users might already have the YUI Library files caches from being on other website and using other application before using yours.

Intra-site/app performance may take a hit at Patay is saying with different pages or screens requiring a different combination of resources.

One possibility would be to load all the possible resources your site/app would ever need using the CDN combo service and referencing that combo file on every page/screen. << Seems that could lead to a large payload of stuff for a user on their first visit/pageview.