Chapter 1. Introduction to JavaScript
JavaScript is a lightweight, interpreted programming language with
object-oriented capabilities. The general-purpose core of the
language has been embedded in Netscape, Internet Explorer, and other
web browsers and embellished for web programming with the addition of
objects that represent the web browser window and its contents. This
client-side version of JavaScript allows executable content to be
included in web pages -- it means that a web page need no longer
be static HTML, but can include programs that interact with the user,
control the browser, and dynamically create HTML content.
Syntactically, the core JavaScript language resembles
C, C++, and Java, with
programming constructs such as the if statement,
the while loop, and the
&& operator. The similarity
ends with this syntactic resemblance, however.
JavaScript
is an untyped language, which means that variables do not need to
have a type specified.
Objects in
JavaScript are more like
Perl's associative arrays than they
are like structures in C or objects in C++ or Java. The
object-oriented
inheritance mechanism of JavaScript is like those of the little-known
languages Self and NewtonScript; it is quite different from
inheritance in C++ and Java. Like Perl, JavaScript is an interpreted
language, and it draws inspiration from Perl in a number of places,
such as its regular expression and array-handling features.
This chapter provides a quick overview of JavaScript; it explains
what JavaScript can and cannot do and exposes some myths about the
language. It distinguishes the core JavaScript language from embedded
and extended versions of the language, such as the client-side
JavaScript that is embedded in web
browsers and the server-side JavaScript that
is embedded in Netscape's web servers. (This book documents
core and client-side JavaScript.) This chapter also demonstrates
real-world web programming with some client-side JavaScript examples.
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