JavaScript 1
Introduction and DOM
Kevin McManus
© 2007
the University of
Greenwich
2
JavaScript 1
What is JavaScript?
•
A
scripting
language developed in a collaboration
between Netscape and Sun Microsystems to provide
client-side programming in web pages
•
Introduced by Netscape in 1995
•
Executable JavaScript may be included into an HTML
page as either...
•
external
•
a separate file containing JavaScript
•
embedded
•
as the content of a
<script>
element
•
inline
•
as the value of an HTML event attribute
© 2007
the University of
Greenwich
3
JavaScript 1
What is JavaScript?
•
Not
a full programming language like Java or C++
•
core language has no graphics, no file handling, no networking
•
Not
a subset of Java - syntactically similar but:
•
loose data typing
•
object based not strictly object oriented
•
although inheritance is possible
•
Not
simple - easy to get started but large and complex
•
client-side code is interpreted by the browser
•
it’s scope is restricted to the browser
•
cannot carry a malicious payload
© 2007
the University of
Greenwich
4
JavaScript 1
Versions of JavaScript
•
Originally introduced in Netscape Navigator 2.0 and Internet Explorer 3.0
•
Very widely used on the web but for "serious applications" held back by:
•
incompatibilities between browsers
•
security issues
•
lack of a good IDE
•
perception of it as a "toy" language
•
these problems are now reducing
•
Exists as:
•
core language
•
client-side version (with client side objects)
•
server-side version (with server side objects)
•
Latest
version is 1.5
•
Microsoft's version is officially called JScript
•
standard version of the core language is called ECMAScript
•
European Computer Manufacturers Association
•
JavaScript 1.3 is reported to be ECMA-262 compatible
© 2007
the University of
Greenwich
5
JavaScript 1
Typical Uses
•
GUI enhancement
•
rollovers images
•
pull-down menus
•
browser sniffing to adjust page layout
•
Techniques to reduce the load on the server
•
validating input before sending to a server-side program
•
shopping carts
•
Mini-applications
•
calculators, calendars
•
Animation
•
Asynchronous applications
•
AJAX
•
Many of the above require DHTML
•
Dynamic HyperText Markup Language
•
combination of JavaScript & HTML & CSS & DOM
© 2007
the University of
Greenwich
6
JavaScript 1
Discussion questions
•
Why might it be a good idea to use JavaScript to
offload work from the server to the client machine?
•
What IPR (intellectual property rights) issues might be
associated with use of JavaScript?
•
Under what circumstance might browser compatibility
issues not be a problem for a JavaScript developer?
•
Can you think of at least two different strategies for
dealing with browser compatibility problems.
© 2007
the University of
Greenwich
7
JavaScript 1
First example
embedding JavaScript in HTML
embed.html
var
age = parseInt(prompt(
"Please enter your age"
, 29));
© 2007
the University of
Greenwich
8
JavaScript 1
First example
embedding JavaScript in HTML
embed.html
alert(
"You look younger than "
+ age)
