Credit: Mulchaey et al (ST Sci/UMD/NASA)
JavaScript is potentially a fully general purpose language that could
conceivably handle any type of problem, but client-side JavaScript
operates within a very restricted environment which tends to specialize
its operations and interactions. Specifically, it
- operates within the domain of a Web client . As
such
it is restricted so that it cannot write anything to the server or
client (except cookies) and cannot read anything from the server
except images and JavaScript programs. However, it can read, write,
and modify cookies on the client machine, and can control almost
every aspect and behavior of a Web browser
- is an interpretive language as opposed to a
compiled language.
As such it is not suitable for compute-intensive
problems, but makes possible an ease and flexibility of programming
that compiled languages lack. This is because machine codes are
not generated in advance, as they are with compiled languages, but
are created when a data object is encountered, and so the language
can adapt itself based on what type of data it sees. Thus if the
language encounters the line
a = b + c
it can generate the appropriate machine code whether a, b, and c
are integers, real numbers, arrays, strings, etc.
- is a secure language. Because it cannot write
anything to the server or client it cannot usually do direct harm
other than crashing your browser. However, this
Cert
Advisory shows you that there do exist some serious security
issues
- is an Object Oriented language . Almost
all modern computer languages are, or are becoming, object oriented.
Examples include C++, Java, Python, Perl, VBScript, and JavaScript.
These languages concentrate on identifying a set of classes and
data definitions and manipulations on objects in these classes
rather than on some overall process. While not suitable for
all problems, it is usually closer to the way we deal with
problems in ordinary life and often brings major simplifications
and flexibility to the code
- is built around the Document Object Model (DOM) of
the
Web. This consists largely of classes of objects and
fits easily into the object oriented nature of JavaScript
- is an Event Driven language. The language
usually operates by reacting to events that are triggered either
explicitly or implicitly by user interactions with the browser,
such as clicking on a button, scrolling down a page, mousing
over a link, etc.
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