Credit: Samuel Zschokke
Many languages can live on either side of the Client/Server
divide, but we will consider only the client-side versions
of JavaScript, JScript, VBScript, and Java. These languages
might be described as follows:
Specific language characteristics: from many standpoints,
JavaScript, JScript, and VBscript can all be considered as a single type,
in that they are all interpreted languages that usually reside inside an
HTML script. JavaScript and Jscript (Microsoft's variant) are almost
identical, and while VBscript has a very different syntax, that of Visual
Basic, it performs the same operations on basically the same types of
objects in the web browser. Java, however, is a very different language.
JavaScript/JScript/VBscript are NOT simple forms of Java, nor are they
simple languages (especially JavaScript and JScript). They share a certain
superficial similarity in syntax and concepts with Java, but differ in
many ways. Although they are much smaller languages than Java, they
posses some subtle concepts that often accompany interpreted
languages.
JavaScript was initially known as LiveScript until its name was changed
for marketing reasons.
Invocation: JavaScript, JScript, and VBscript are typically stored
inside the HTML code as plain text segments inside special tags, and
are transferred from the server to the client
browser when the HTML is invoked through a URL. At that point they may
simply start executing (even before the rest of the HTML is loaded), may
execute when directed by an "onLoad" directive, or may be invoked by
mouse, scroll, or keyboard actions by the user.
Java Applets are also loaded from the server when the HTML is invoked by
the URL, but the code that is loaded is not plain text: it consists of
precompiled "class" files. And the activation
is done through special applet tags of the form <APPLET >. These
forms contain parameters which you can use to tailor the operation of the
applet. Once invoked, the applet can present you with various HTML
elements, including buttons, as well as highly interactive graphics.
Like JavaScript, once loaded the applet runs only on the client.
See this
for a sample Java
Applet.
Characteristics: they run on the client, are very fast and
responsive (once loaded), they have an intimate knowledge of the browser
environment (see this
for an example
taken from Goodman's JavaScript book which manipulates all possible HTML
form elements),
and (under DHTML) can manipulate nearly all of its elements.
See
this for an example of very fast and
responsive animation.
Limitations: they have very limited access to the server, and little
access to the client machine itself, except for cookies. See
this
for a simple example of cookies, and this
for a more comlex and useful example.
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