September 2007
Intermediate to advanced
170 pages
4h 24m
English
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Putting It in Perspective
These examples use a script that takes 10 seconds to download. Hopefully, the delay isn't as long for any scripts you use, but it is possible for a script to take longer than expected and for the user's bandwidth to affect the response time of a script. The effect that scripts have on your pages might be less than shown here, but it could still be noticeable. Having multiple scripts in your page compounds the problem.
In some situations, it's not easy to move scripts to the bottom.
If, for example, the script uses document.write to insert part of the page's
content, it can't be moved lower in the page. There might also be
scoping issues. In many cases, there are ways to work around these
situations.
An alternative suggestion that comes up often is to use deferred scripts. The DEFER attribute indicates that the script does
not contain document.write, and is a
clue to browsers that they can continue rendering. You can see this in
the following example.
- Deferred Scripts
Unfortunately, in Firefox, even deferred scripts block rendering and parallel downloads. In Internet Explorer, components lower in the page are downloaded slightly later. If a script can be deferred, it can also be moved to the bottom of the page. That's the best thing to do to speed up your web pages.
Move scripts to the bottom of the page.
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.