Tuesday, November 25th, 2008
It actually now looks like Minefield (Firefox nightly) is getting 10 out of 11, and the other browsers are doing great too.
Jonas Sicking of Mozilla has a really nice comment that talks about what the engines are doing and some nuances. For example, if you have a CSS file and a JS file, do you block just in case the JS looks into CSS values (e.g. “in case there is a call to .offsetTop in the script”). How about looking ahead to see? That is the case. You can download away and try to do the right thing. document.write() is another beast that seems to do a lot of harm. Having the browser be smart about it (“they don’t do that”) will be good.
Back to John, he also discusses features that we can use as developers:
This is part of the HTML 5 specification and allows for pages to specify resources which should be opportunistically downloaded in case they should be used in the future (the common example of image rollovers could be used here).HTML4< view plain text >
- <link rel="prefetch" href="/images/big.jpeg">
And that resource will be downloaded preemptively.
The final case that the profiler tests for is the ability of a browser to support inline images using a data: URI. Data URIs give developers the ability to include the image data directly within the page itself. While this saves an extra HTTP request it’s important to note that the resource will not be cached (at least not as external resource – it may be cached as part of the complete page). The use of this technique will vary on a case-by-case basis but having a browser support it is absolutely important.
Posted by Dion Almaer at 9:16 am