Java Scripts

Java Script

Java Script is the programming language of HTML and the Web.

JavaScript is easy to learn...

What is JavaScript?

JavaScript is a dynamic computer programming language. It is lightweight and most commonly used as a part of web pages, whose implementations allow client-side script to interact with the user and make dynamic pages. It is an interpreted programming language with object-oriented capabilities.

JavaScript was first known as Live Script, but Netscape changed its name to JavaScript, possibly because of the excitement being generated by Java. JavaScript made its first appearance in Netscape 2.0 in 1995 with the name Live Script. The general-purpose core of the language has been embedded in Netscape, Internet Explorer, and other web browsers.

Specifications

JavaScript is a lightweight, interpreted programming language.
Designed for creating network-centric applications.
Complementary to and integrated with Java.
Complementary to and integrated with HTML.
Open and cross-platform.

Advantages of JavaScript

Less server interaction − You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.
Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.
Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.
Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.

Limitations of JavaScript

Client-side JavaScript does not allow the reading or writing of files. This has been kept for security reason.
JavaScript cannot be used for networking applications because there is no such support available.
JavaScript doesn't have any multi-threading or multiprocessor capabilities.

Why JavaScript?

JavaScript is one of the 3 languages all the web developer must learn:

HTML to define content of web pages.
CSS to specify the layout of web page.
JavaScript to program the behavior of web pages.

Web Pages are not only the place where JavaScript is used. Many desktops and the server programs use JavaScript. Node.js is the best known. Some databases, like MongoBD and CouchDB, also use JavaScript as their programming language.

The primary purpose of JavaScript is to provide a better experience for the user. It manipulates the objects within the HTML document. The objects and HTML elements collectively form what we call the Document Object Model(DOM).

Did You Know?

JavaScript and Java are completely different languages, both in concept and design.
JavaScript was invented by Brendan Eich in 1995, and became an ECMA standard in 1997.
ECMA-262 is the official name of the standard. ECMAScript is the official name of the language.

What exactly does JavaScript do?

It allows programming to be performed without server interaction.
It can respond to events, such as button clicks.
It can validate data before sending out a request.
It can adjust an HTML document for special effects.
It can create cookies! Cookies can be used to store and retrieve information from the user's computer.

What JavaScript implementations are available?

The Mozilla project provides two JavaScript implementations. The first ever JavaScript was created by Brendan Eich at Netscape, and has since been updated to ECMA-262 Edition 5 and later versions. This engine, code named SpiderMonkey, is implemented in C/C++. The Rhino engine, created primarily by Norris Boyd(also at Netscape) is a JavaScript implementation written in Java. Like SpiderMonkey, Rhino is ECMA-262 Edition 5 compliant.

Several major runtime optimizations such as TraceMonkey (Firefox 3.5), JagerMonkey (Firefox 4) and Ionmonkey were added to the SpiderMonkey JavaScript engine overtime. Work is always ongoing to improve JavaScript execution performance.

Besides the above implementations, there are other popular JavaScript engines such as:-

Google's V8, which is used in the Google Chrome browser and recent versions of Opera browser. This is also the engine used by Node.js.
The JavaScripitCore (SquirrelFish/Nitro) used in some WebKit browsers such as Apple Safari.
Carakan in old version of Opera.
The Chakra engine used in Internet Explorer (although the language it implements is formally called "JScript" in order to avoid trademark issues.)

Each of Mozilla's JavaScript engines expose a public API which application developers can use to integrate JavaScript into their software. By far, the most common host environment for JavaScript is web browsers. Web browsers typically use the public API to create host objects responsible for reflecting the DOM into JavaScript.

Another common application for JavaScript is as a (web) server side scripting language. A JavaScript web server would expose host objects representing a HTTP request and response objects, which could then be manipulated by a JavaScript program to dynamically generate web pages. Node.js is a popular example of this.

JavaScript Resources

SpiderMonkey

Information specific to Mozilla's implementation of JavaScript in C/C++ engine(aka SpiderMonkey), including how to embed it in applications.

Rhino

Information specific to the JavaScript implementation written in Java(aka Rhino).

Language resources

Pointers to published JavaScript standards.

A re-introduction to JavaScript

JavaScript guide and JavaScript reference.

Development Tools

Important tools have evolved with the language.

Every major web browser has built-in web development tools, including JavaScript debugger.
Static program analysis tools, such as ESLint and JSLint, scan JavaScript code for conformance to a set of standard and guidelines.
Some browsers have built-in profilers. Standalone profiling libraries have also been created, such as benchmark.js and jsbench.
Many text editors have syntax highlighting support for JavaScript code.