|
What is JAVA SCRIPT?
JavaScript is a scripting language
designed primarily for adding interactivity to Web pages and creating
Web applications. The language was first implemented by Netscape
Communications Corp. in Netscape Navigator 2 beta (1995). JavaScript is
different from the Java language (developed in the 1990s at Sun
Microsystems). However, the two languages can interoperate well.
Client-side JavaScript
programs, or scripts, can be embedded directly in HTML source of Web
pages. (Note:
There is also server-side JavaScript,
but it's beyond the scope of this FAQ collection.) Depending on the Web
developer's intent, script code may run when the user opens the Web
page, clicks or drags some page element with the mouse, types something
on the keyboard, submits a form, or leaves the page.
JavaScript is an object-oriented language
with prototypal inheritance.
The language supports several built-in objects, and programmers can
create or delete their own objects. Prototypal inheritance makes
JavaScript very different from other popular programming languages such
as C++, C#, or Java featuring classes
and classical inheritance.
JavaScript does not have classes in the C++ or Java sense. In
JavaScript, objects can inherit properties directly from each other,
forming the object prototype chain.
JavaScript is an interpreted language,
with optional JIT-compilation
support. In older implementations (e.g. Internet Exlorer 8 and earlier,
Firefox prior to 3.5), JavaScript was a purely
interpreted language.
This means that scripts execute without preliminary
compilation, i.e.
without conversion of the script text into system-dependent machine
code. The user's browser interprets
the script, that is, analyzes and immediately executes it. In modern
implementations, JavaScript code may be either interpreted or compiled
using a just-in-time
(JIT) compiler. At run time, the browser decides whether (parts of)
script code should be JIT-compiled for better performance. This makes
JavaScript significantly faster
and therefore more suitable for complex performance-demanding Web
applications. Recent versions of all popular browsers have JavaScript
JIT-compilers
|