Brett Patterson skrev:
> I am in the middle of a conversation with this guy who says that
JavaScript is an object-oriented language. Is he correct? Could you
please site some references?
I have read the whole thread up until now, but will answer your starting
message, since I am not addressing a single specific respondent.
I am in charge of developing DOM Scripting courses for the Curriculum
Framework of the WaSP Education Task Force[1]
I have therefore tried to read every single resource about JavaScript,
ECMAScript and the DOM that has been written from a computer science
perspective. There are not that many, which might be a reason behind the
confusion.
Anyway: JavaScript (a term owned by Sun, licensed to Mozilla, and used
by all browser vendors but Microsoft) is in all essence, as Liorean has
stated, a superset of ECMAScript 3.0. That is also the sentiment of
Brendan Eich - and should therefore be taken as a final word. (Anthony
was indeed wrong about this.) JScript as implemented in Internet
Explorer is roughly equivalent, but deviates in some small ways.
JavaScript is a mix of Self, Scheme and C (according to the ECMAScript
3.1 draft, the "love child between Scheme and C" according to Brendan Eich).
JavaScript is indeed Object Oriented, but even though every script is
run within a host object - usually the window object of a browser - a
procedural style is possible to use. 90's DHTML scripts were usually
procedural and used document.write (which is not ECMAScript but part of
the DOM) in a way that reminds me of *standard streams*, which could be
provided by the host object, but usually aren't.
Public, private and protected methods and properties are not easily
implemented. Object Oriented design patterns (singletons, factories,
registry, adaptors...) can usually be emulated. Sometimes this is only
done through considerable wizardry using concepts like lambda and closures.
ECMAScript 4.0 aka JavaScript 2.0 was supposed to get a limited class
based inheritance mechanism to *complement* the prototype based one we
use today. Those plans have been halted. ECMAScript "Harmony" will most
probably *not* get any class based inheritance.
(At least two JavaScript engines (V8 and Squirrelfish Extreme) emulate
class based object creation as part of their just in time compilation,
but that really is a compiler issue.)
ECMASCript 3.1 will get a few new methods to facilitate easier
inheritance patterns. E.g. Object.freeze(). Many popular libraries also
have methods that facilitate OO-patterns.
As old school cut' n' paste coding is getting superseded by libraries
procedural code is becoming less seen and OO-style coding is getting
more used.
Indeed, using object chaining in JQuery et al, the programming is even
well on its way to become *declarative*.
Summary:
1. JavaScript *is* OO.
2. JavaScript uses a prototypal - class-less - inheritance mechanism.
3. Anyone writing a script can use procedural style, OO-style or even
make forays into a declarative style.
Nit picking on some stuff in the thread:
JavaScript has no pure hash-tables, aka associative arrays. Object
properties can be used to emulate associative arrays, though. A PHP
programmer will feel very limited, though.
A JavaScript object *is* not an array (once again Anthony got it wrong).
It can have methods as well as properties. <aside>Arrays are however
objects, and confusingly
typeof [ 1, 2 ]
evalutes to "object", not "array". A major design flaw.
The best known way to test for an array is:
Object.prototype.toString.apply(value) === '[object Array]'
Discovered by Mark Miller of Google.</aside>
From a very strict computer science point of view averything in
JavaScript is *not* an object. (No matter how much Alex "Dojo" Russel et
al. reiterates that mantra.) In practice everything is. JavaScript has
got a few "primitives" (numbers, strings, booleans, undefined). Whenever
a primitive is referenced with an OO-syntax it is converted into its
corresponding wrapper object. This was modeled after Java according to
Brendan, and he has stated that it probably was a bad idea. (Search the
ES4 mailing list for a reference.)
Lars Gunther
Sources:
MDC, including https://developer.mozilla.org/En/About_JavaScript
ES 3.0 spec
ES 3.1 spec draft
"JavaScript, The Definitive Guide" (latest edition)
ES3.1 mailing list
ES 4/Harmony mailing list
Doug Crockfords site and book ("JavaScript, the good parts")
Numerous other JavaScript books
1.
http://www.webstandards.org/2008/07/31/announcing-the-wasp-curriculum-framework/
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