软件名称： Beginning JavaScript with DOM Scripting and Ajax
软件介绍
If you want to learn about Javas cript from scratch—what it is, what to use it for, and how to
make it work with other technologies like CSS and HTML—you have picked up the right book.
If you already have a considerable amount of experience with Javas cript, but want to bring your
knowledge up to date, you have also picked up the right book—a lot has changed in Javas cript
development in recent years.
When Javas cript first started being used for web development back in the mid-to-late
1990s (it was first supported in Netscape 2, back in 1996), it quickly became much maligned, for
many reasons—browser support was mediocre at best, and at worst, you actually had different
Javas cript functions being implemented in different ways by different browsers (Netscape 4
and Internet Explorer 4 were major culprits, at the height of the so-called browser wars). This
led to developers having to write completely different versions of web sites or indulge in messy
code forking, if they wanted to attempt to have cross-browser support.
And that was the consciencious ones—Javas cript’s bad reputation was just as much the
fault of the developers as the browser manufacturers. Developers back in those days tended to
use Javas cript for all manner of flashy effects that looked cool, but caused all manner of prob-
lems in terms of usability and accessibility (the days of DHTML—another marketing buzzword
back in the day, which referred to the application of Javas cript, CSS, and HTML to produce
dynamic effects). Pages would break completely if Javas cript was unavailable for any reason or
if the user was trying to use a screenreader. And a lot of web developers would copy and paste
s cripts into their web sites without understanding how they actually worked, causing more
untold usability and code maintenance nightmares.
But as I said earlier, things have changed. Browser support is now at a manageable level,
with the modern browsers largely using the same implementation of the Document Object
Model and other constructs, and modern techniques are a lot more considerate of accessibility,
etc. As you’ll learn through the course of this book, modern techniques like DOM s cripting are
built around the premise of separating out not only the structure (in your markup) and the
presentation (in your CSS), but also the behavior in your Javas cript files (not interspersed
through your markup documents). Javas cript does not have to be evil—you can code your web
sites so that the Javas cript enhancements you are using can add to the experience of users who
can take advantage of them, but they don’t break when Javas cript is not available. This is called
unobtrusive Javas cript—Javas cript enhancements should be seen as a bonus for those who can
use them, not an essential feature for the running of a site.
If you’ve used Javas cript before, then be prepared to take on a new mindset as you step
forward through the book. If you are completely new to Javas cript, then breathe a sign of relief
and consider yourself lucky that you never had to suffer the early days of Javas cript develop-
ment that I just touched on!
make it work with other technologies like CSS and HTML—you have picked up the right book.
If you already have a considerable amount of experience with Javas cript, but want to bring your
knowledge up to date, you have also picked up the right book—a lot has changed in Javas cript
development in recent years.
When Javas cript first started being used for web development back in the mid-to-late
1990s (it was first supported in Netscape 2, back in 1996), it quickly became much maligned, for
many reasons—browser support was mediocre at best, and at worst, you actually had different
Javas cript functions being implemented in different ways by different browsers (Netscape 4
and Internet Explorer 4 were major culprits, at the height of the so-called browser wars). This
led to developers having to write completely different versions of web sites or indulge in messy
code forking, if they wanted to attempt to have cross-browser support.
And that was the consciencious ones—Javas cript’s bad reputation was just as much the
fault of the developers as the browser manufacturers. Developers back in those days tended to
use Javas cript for all manner of flashy effects that looked cool, but caused all manner of prob-
lems in terms of usability and accessibility (the days of DHTML—another marketing buzzword
back in the day, which referred to the application of Javas cript, CSS, and HTML to produce
dynamic effects). Pages would break completely if Javas cript was unavailable for any reason or
if the user was trying to use a screenreader. And a lot of web developers would copy and paste
s cripts into their web sites without understanding how they actually worked, causing more
untold usability and code maintenance nightmares.
But as I said earlier, things have changed. Browser support is now at a manageable level,
with the modern browsers largely using the same implementation of the Document Object
Model and other constructs, and modern techniques are a lot more considerate of accessibility,
etc. As you’ll learn through the course of this book, modern techniques like DOM s cripting are
built around the premise of separating out not only the structure (in your markup) and the
presentation (in your CSS), but also the behavior in your Javas cript files (not interspersed
through your markup documents). Javas cript does not have to be evil—you can code your web
sites so that the Javas cript enhancements you are using can add to the experience of users who
can take advantage of them, but they don’t break when Javas cript is not available. This is called
unobtrusive Javas cript—Javas cript enhancements should be seen as a bonus for those who can
use them, not an essential feature for the running of a site.
If you’ve used Javas cript before, then be prepared to take on a new mindset as you step
forward through the book. If you are completely new to Javas cript, then breathe a sign of relief
and consider yourself lucky that you never had to suffer the early days of Javas cript develop-
ment that I just touched on!
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