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About JavaScript

History and naming
JavaScript was originally developed by Brendan Eich of Netscape under the name Mocha, which was later renamed to LiveScript, and finally to JavaScript.[5] The change of name from LiveScript to JavaScript roughly coincided with Netscape adding support for Java technology in its Netscape Navigator web browser. JavaScript was first introduced and deployed in the Netscape browser version 2.0B3 in December 1995. The naming has caused confusion, giving the impression that the language is a spin-off of Java, and it has been characterized by many as a marketing ploy by Netscape to give JavaScript the cachet of what was then the hot new web-programming language.

Microsoft named its dialect of the language JScript to avoid trademark issues. JScript was first supported in Internet Explorer version 3.0, released in August 1996, and it included Y2K-compliant date functions, unlike those based on java.util.Date in JavaScript at the time. The dialects are perceived to be so similar that the terms "JavaScript" and "JScript" are often used interchangeably. Microsoft, however, notes dozens of ways in which JScript is not ECMA compliant.

Netscape submitted JavaScript to Ecma International for standardization resulting in the standardized version named ECMAScript.

The flexibility of JavaScript has made it one of the most popular programming languages on the web and also one of the easier languages to learn. In regards to demographics, the language is extremely widespread in India with the United States, Russia and Ukraine also using it as a staple in their online programming. As the web continues to expand, the use of JavaScript looks like it will become more popular especially in Europe and Asia.

Features

Imperative and structured

JavaScript supports all the structured programming syntax in C (e.g., if statements, while loops, switch statements, etc.). One partial exception is scoping: C-style block-level scoping is not supported. JavaScript 1.7, however, supports block-level scoping with the let keyword. Like C, JavaScript makes a distinction between expressions and statements.

Dynamic

dynamic typing As in most scripting languages, types are associated with values, not variables. For example, a variable x could be bound to a number, then later rebound to a string. JavaScript supports various ways to test the type of an object, including duck typing. Objects as associative arrays
JavaScript is almost entirely object-based. Objects are associative arrays, augmented with prototypes (see below). Object property names are associative array keys: obj.x = 10 and obj["x"] = 10 are equivalent, the dot notation being merely syntactic sugar. Properties and their values can be added, changed, or deleted at run-time. The properties of an object can also be enumerated via a for...in loop.

Run-Time evaluation
JavaScript includes an eval function that can execute statements provided as strings at run-time.

Functional
First-Class functions


Functions are first-class; they are objects themselves. As such, they have properties and can be passed around and interacted with like any other object.

Inner functions and closures
Inner functions (functions defined within other functions) are created each time the outer function is invoked, and variables of the outer functions for that invocation continue to exist as long as the inner functions still exist, even after that invocation is finished (e.g. if the inner function was returned, it still has access to the outer function's variables) - this is the mechanism behind closures within JavaScript.

About JavaScript

prototypes

JavaScript uses prototypes instead of classes for defining object properties, including methods, and inheritance. It is possible to simulate many class-based features with prototypes in JavaScript.

functions as object constructors

Functions double as object constructors along with their typical role. Prefixing a function call with new creates a new object and calls that function with its local this keyword bound to that object for that invocation. The function's prototype property determines the new object's prototype. functions as methods

Unlike many object-oriented languages, there is no distinction between a function definition and a method definition. Rather, the distinction occurs during function calling; a function can be called as a method. When a function is invoked as a method of an object, the function's local this keyword is bound to that object for that invocation.

Miscellaneous

Run-Time Environment
JavaScript typically relies on a run-time environment (e.g. in a web browser) to provide objects and methods by which scripts can interact with "the outside world". (This is not a language feature per se, but it is common in most JavaScript implementations.)

Variadic Functions An indefinite number of parameters can be passed to a function. The function can both access them through formal parameters and the local arguments object.

Array and Object Literals
Like many scripting languages, arrays and objects (associative arrays in other languages) can each be created with a succinct shortcut syntax.

In fact, these literals form the basis of the JSON data format.

Regular Expressions

JavaScript also supports regular expressions in a manner similar to Perl, which provide a concise and powerful syntax for text manipulation that is more sophisticated than the built-in string functions.

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