Alrighty, this is something I've talked about last year at HighLoad++ and Fronteers, but never blogged. I came up with this thing while at Yahoo! Search and we used it there in production. So, it must be working. While probably not practical for many sites, the takeaway might very well be: optimizations are all around us, we just have to look around for them.
The summary: browsers have built-in search boxes which also give you search suggestions. IE8+ have added visual search suggestions, meaning images. The trick here is - when you don't have a visual suggestion, why not "suggest" an image for preloading, such as a sprite. Or two.
On to the details.
Every browser these days has them search boxes. Usually in the upper right. Like this:
(Aside rant: I call these browser search boxes "chrome search", but with the advent of the Chrome browser by Google and the fact that Google does search, this is now confusing, even doubly so. So next time you name a project or a company using a name that is already full of meaning such as Chrome or Closure, you're just being unimaginative and.. yeah, not cool. Unless of course it's something like Apple that's too far off from the actual product.)
Chrome search suggestions
Depending on how the search provider was set up, while you type the browser can send the partial string you typed to a URL of the search provider's choice. The search provider then can return a list of suggestions.
BTW, you don't have to be Google or Yahoo in order to be a search provider. This is "open search" and any site could (and frankly, should) be a search provider, here's an example how.
Visual chrome search suggestions
Starting with IE8, the provider can not only offer textual suggestions, but also visual ones, meaning images. So if you look up a stock symbol, it can give you a chart. Or a weather forecast.
The search provider sends back JSON or XML to the browser. The visual thing requires XML actually. Here's more from the horse's mouth. So in order to send an image back you use a syntax like so:
... <Item> <Text>Currently: Partly Cloudy, 67F</Text> <Description>High: 71F Low: 63F</Description> <Url>http://weather.yahoo.com/forecast/ USCA1024_f.html</Url> <Image source="http://path/to/my/image.png" alt="Partly Cloudy" width="31" height="31"/> </Item> ...
Preload in visual chrome search suggestions
So what if you don't have an appropriate image for a search term? Or maybe a partial term, say like for example "sch"? Why not load a sprite or some other image, hidden, 0x0 instead. Something that you can be reasonably confident the user will need once they get to the search results page. Easy-peasy:
... <Item> <Text>schmuck</Text> <Url>http://whatever.org</Url> <Image source="http://path/to/my/sprite.png" width="0" height="0"/> </Item> ...
This way you're in effect preloading something that will be needed later. I mean once the user starts typing, there's a pretty decent chance they'll end up on the results page. And they are likely to prefer a fast results page. It will be fast when pieces of it were pre-downloaded.
And if you inspect what's going on in HTTPWatch, you can see that as you type, the browser sends a request to the search provider, which then returns an XML document. And an image, although no image is seen.
What didn't work
I tried preloading CSS and JS too, but it didn't work. These show broken image icons, even with 0x0 size. I also tried 1x1 but then there's a 1x[LINE-HEIGHT] grey square/line.
And that's that
So here - a way to preload images for free, by simply using a browser feature.
You can also use this to preload 1x1 beacons for DNS resolution purposes. Say you serve search suggestions from suggest.example.org but the results are on www.example.org and the static stuff is on static1.example.org, static2.example.org, etc. There's an opportunity to pre-resolve all these domain names by requesting a tiny image from each.
Thanks for reading, this was the second post from the Velocity countdown. Only 5 more days to go! Hope you learned something, even if you don't intend to use it right away. Or maybe at least you've decided to offer your site as a search provider to all browsers. Free marketing, why not?
See you tomorrow.