Tài liệu JavaScript: The Definitive Guide

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.