by Hayesha Somarathna

During the past series of articles I focus your attention on various Web based technologies and their best practices in their day today application. Today with this article I'm going to introduce another important technology that has revolutionized the World Wide Web over the past decade. This we can call as the world's most misunderstood language. It's called the JavaScript. It's a small language specially designed for work within the context a of Web browser. The JavaScript language has many implementations like LiveScript, JScript, ECMAScript, etc... and its original implementation was derived from LiveScript. Microsoft Corporation developed a compatible dialect of the language, naming it JScript to avoid Trademark issues. Today every personal computer in the world has at least one JavaScript interpreter installed on it and in active use. Although the popularity of JavaScript among the user community is it being just a scripting language with limited capabilities but it's a nice, dynamic object-oriented general-purpose programming language having features like Load and Go delivery, Loosely typed, Prototypal Inheritance, Lambda, Linkage through global variables, Objects, etc...

JavaScript is not Java although it has the suffix Java appends to it. It came out as such due to the alliance that the Netscape Corporation had with Sun Microsystems. They are two very different languages. JavaScript is not a subset of Java. It is not interpreted Java. JavaScript shares C-family syntax with Java, but at a deeper level it shows greater similarity to the functional languages like Scheme and Lisp. It is a small language, but it is also a surprisingly powerful and expressive language.

History

JavaScript was developed by Brendan Eich at Netscape Corporation as the in-page scripting language for Netscape Navigator 2. The original version was first called as LiveScript which ran both on client-side as well as server-side under its special platform. As mentioned above the JavaScript was born through the alliance of Netscape Corporation and Sun Microsystems.      Because of its linkage to web browsers, it instantly became massively popular. It never got a trial period in which it could be corrected and polished based on actual use. The language is powerful and flawed. The language is not complete due to the flaws in its standards specification which got approved in a forum held at European Computer Manufactures Association (ECMA), a Switzerland-based standards body.

Data Types in JavaScript

JavaScript comes with a small set of data types. It has three primitive types String, Number and Boolean and two other special values called null and undefined. Other than that everything in this language are considered as Objects. 

String in this language is a sequence of 0 or more 16-bit characters having a character encoding of UCS-2 not of UTF-16 and the current version supports Unicode. It has no separate character types; it represents a character as a string of length of 1. Strings are immutable.

Only one number type is available and there is not such type called integers. Number is 64-bit floating point, aka IEEE-754, similar to Java's double and Double. The division between two integers always produces a fractional result. Number also includes the special values NaN (not a number) and Infinity.

Boolean has two values, namely true and false. Nulls always gives a null while undefined is a special value that the default value assigned to any of the variable unless they are initialized.

Loosely typed

It's a language that each variable has a special value undefined by default at the declaration of the variable until it is assigned with a specific type, such as number, string, boolean, etc... The language variables are loosely typed but they aren't untyped.

Reserved Words

It’s a language with a bag full of key words that lets the programmer to get the work done easily with minimum effort. So have to be careful in using reserve words.       

abstract
boolean break byte
case catch char class const continue
debugger default delete do double
else enum export extends
false final finally float for function
goto
if implements import in instanceof int interface
long
native new null
package private protected public
return
short static super switch synchronized
this throw throws transient true try typeof
var volatile void
while with

Objects

Everything used in the language are objects. An object is an unordered collection of name/value pair. Names are strings while values are of any type including other objects. Every object is a little database. Object literals can be used anywhere a value can appear.

Eg:

var myObject = {name: "Hayesha Somarathne", 'country': 'Sri Lanka', gender: 'Male'};

var theName = myObject.name;

var country = myObject['country'];

Instead of creating an object directly we also can make use of the Maker function to create one.

function maker(name, country, gender) {

    var it = {};

    it.name = name;

    it['country'] = country;

    it.gender = gender;

    return it;

}

myObject = maker("Hayesha Somarathne", ' Sri Lanka', 'Male’);

In the following example you will see that JavaScript provides the facility to create object(s) within an object.

var myObject = {

    name: "Hayesha Somarathe",

    'country': 'Sri Lanka',

     gender: 'Male',

     format: {

        color: 'fair',

        weight: 60,

        height: 168

    }

};

Prototypal Inheritance

In most languages we encounter consists of classes, methods, constructors and modules. The JavaScript’s functions do all of those. Instead of the classical Inheritance JavaScript comes with Prototypal Inheritance. This accomplishes the same thing but in a different manner and it offers greater expressive power. Instead of organizing objects into rigid classes, new objects can be made that are similar to existing objects, and then customized. Object customization is less work than making a class, and less overhead, too.

One of the keys is the object(o) function and other key is functions. Objects can be passed as arguments to functions, and can be returned by functions. They are passed by reference and not as passed by value.

Summary

Over the Internet you’ll be able to find enough articles written on JavaScript explaining various aspects of it usage. But in this article I tried to focus your attention on the JavaScript scripting language in a bit of a different dimension to make you understand the real power built into it. I have introduced a list of the language features in the beginning but have only extend the discussion on few of them, so its up to you go further and explore more into them to feel the real power of it and make use the language features effectively in your future attempts. 

Reference:

Douglas Crockford, JavaScript: The Good Parts

http://developer.yahoo.com/yui/theater/

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