Ajax Performance

The WebKit team makes the case for preloading

Over at Surfin’ Safari, Antti Koivisto explains the preloading features in the latest WebKit nightlies. Antti begins by documenting the dominance of latency in determining total page load time, focusing on the slowdown caused by the blocking behavior of modern browsers while handling external scripts. As we’ve discussed here in the past, this has the effect of serializing object loads resulting in a total page load time that increases linearly with increases in network latency.

The new preloading feature available in WebKit nightlies attempts to maintain network parallelization even while the parser is blocked waiting for an external script to load. To achieve this, a separate parser is created to move through the remainder of the page, queuing up any additional objects to load. Scripts and stylesheets are also moved to the head of the queue of pending objects.

The net result for end users is a faster page load:

It should be noted that IE8 promises a similar improvement to script load parallelization, as discussed by Steve Souders a few weeks back. I would guess that the underlying implementation is similar to that used by the WebKit team.