JavaScript Information (Scripting Language) @ AvailableWebsites.net

JavaScript is primarily used in the form of client-side JavaScript Client-side JavaScript is JavaScript that runs on client-side. While JavaScript was originally created to run on client-side, this term was coined because the language is no longer limited to just client-side, e.g. server-side JavaScript (SSJS) is also available, implemented as part of a web browser A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to in order to provide enhanced user interfaces In the industrial design field of human-machine interaction, the user interface is where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the machine which aids the operator in making operational decisions and dynamic websites A website is a collection of related web pages, images, videos or other digital assets that are addressed relative to a common Uniform Resource Locator (URL), often consisting of only the domain name, or the IP address, and the root path ('/') in an Internet Protocol-based network. A web site is hosted on at least one web server, accessible via a. However, its use in applications Application software, also known as applications or apps, is computer software designed to help the user to perform singular or multiple related specific tasks. Examples include Enterprise software, Accounting software, Office suites, Graphics software and media players outside web pages is also significant.

JavaScript and the Java programming language Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode (class file) both use syntaxes influenced by that of C C is a general-purpose computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system syntax Curly brace or bracket programming languages are those which use balanced brackets , also known as "squiggly brackets", "brace brackets" or simply "braces", to make blocks in their syntax or formal grammar, mainly due to being C-influenced. The main alternate style is the use of paired keywords, although some, and JavaScript copies many Java names and naming conventions; but the two languages are otherwise unrelated and have very different semantics. The key design principles within JavaScript are taken from the Self Self is an object-oriented programming language based on the concept of prototypes. It was used mainly as an experimental test system for language design in the 1980s and 1990s. In 2006, Self was still being developed as part of the Klein project, which was a Self virtual machine written fully in Self. The latest major version is 4.3, which was and Scheme Scheme is one of the two main dialects of the programming language Lisp. Unlike Common Lisp, the other main dialect, Scheme follows a minimalist design philosophy specifying a small standard core with powerful tools for language extension. Its compactness and elegance have made it popular with educators, language designers, programmers, programming languages.^[8]

History

Anyway I know only one programming language A programming language is an artificial language designed to express computations that can be performed by a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine, to express algorithms precisely, or as a mode of human communication worse than C and that is Javascript. [...] I was convinced that we needed to build-in a programming language, but the developers, Tim Sir Timothy John "Tim" Berners-Lee, OM, KBE, FRS, FREng, FRSA , is a British engineer and computer scientist and MIT professor credited with inventing the World Wide Web, making the first proposal for it in March 1989. On 25 December 1990, with the help of Robert Cailliau and a young student at CERN, he implemented the first successful first, were very much opposed. It had to remain completely declarative. Maybe, but the net result is that the programming-vacuum filled itself with the most horrible kluge in the history of computing: Javascript.

Robert Cailliau Robert Cailliau , born 26 January 1947, is a Belgian informatics engineer and computer scientist who, together with Sir Tim Berners-Lee, developed the World Wide Web^[9]

JavaScript was originally developed by Brendan Eich Brendan Eich (born 1961) is a computer programmer and creator of the JavaScript scripting language. He is the chief technology officer at the Mozilla Corporation of Netscape under the name Mocha, which was later renamed to LiveScript, and finally to JavaScript. ^[10] ^[11] LiveScript was the official name for the language when it first shipped in beta releases of Netscape Navigator 2.0 in September 1995, but it was renamed JavaScript in a joint announcement with Sun Microsystems on December 4, 1995 ^[12] when it was deployed in the Netscape browser version 2.0B3. ^[13]

The change of name from LiveScript to JavaScript roughly coincided with Netscape adding support for Java technology in its Netscape Navigator Netscape Navigator and Netscape are the names for the proprietary web browser popular in the 1990s, the flagship product of the Netscape Communications Corporation and the dominant web browser in terms of usage share, although by 2002 its usage had almost disappeared. This was partly due to the increased usage of Microsoft's Internet Explorer web web browser A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to. The final choice of name caused confusion, giving the impression that the language was a spin-off of the Java programming language Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode (class file), and the choice 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. ^[14] ^[15] It has also been claimed that the language's name is the result of a co-marketing deal between Netscape Netscape Communications is a US computer services company, best known for its web browser. When it was an independent company, its headquarters were in Mountain View, California. The name Netscape was a trademark of Cisco Systems, that was granted to the company and Sun Sun Microsystems, Inc. is a wholly owned subsidiary of Oracle Corporation, selling computers, computer components, computer software, and information technology services. Sun was founded on February 24, 1982. The company was headquartered in Santa Clara, California , on the former west campus of the Agnews Developmental Center, in exchange for Netscape bundling Sun's Java runtime with their then-dominant browser A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to.^{[citation needed]}

JavaScript very quickly gained widespread success as a client-side scripting language for web pages. As a consequence, Microsoft Microsoft Corporation is a public multinational corporation based in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions. Established on April 4, 1975 to develop and sell BASIC interpreters for the Altair 8800, developed a compatible dialect of the language, naming it JScript JScript is a scripting language based on the ECMAScript standard that is used in Microsoft's Internet Explorer to avoid trademark issues. JScript added new date methods to fix the non-Y2K The Year 2000 problem was a notable problem for both digital (computer-related) and non-digital documentation and data storage situations which resulted from the practice of abbreviating a four-digit year to two digits-friendly methods in JavaScript, which were based on java.util.Date.^[16] JScript was included in Internet Explorer Windows Internet Explorer , is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995. It has been the most widely used web browser since 1999, attaining a peak of about 95% usage share during 2002 and 2003 with IE5 and IE6 3.0, released in August 1996. 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.^[17])

In November, 1996 Netscape announced that it had submitted JavaScript to Ecma International Ecma International is an international, private (membership-based) non-profit standards organization for information and communication systems. It acquired its name in 1994, when the European Computer Manufacturers Association (ECMA) changed its name to reflect the organization's international reach. As a consequence, the name is no longer for consideration as an industry standard, and subsequent work resulted in the standardized version named ECMAScript ECMAScript is the scripting language standardized by Ecma International in the ECMA-262 specification and ISO/IEC 16262. The language is widely used for client-side scripting on the web, in the form of two well-known dialects, JavaScript and JScript. Another well-known dialect is ActionScript.^[18]

JavaScript has become one of the most popular programming languages on the web. Initially, however, many professional programmers denigrated the language because its target audience was web authors and other such "amateurs", among other reasons.^[19] The advent of Ajax Ajax is a group of interrelated web development techniques used on the client-side to create interactive web applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page. The use of Ajax techniques has led to an increase in returned JavaScript to the spotlight and brought more professional programming attention. The result was a proliferation of comprehensive frameworks and libraries, improved JavaScript programming practices, and increased usage of JavaScript outside of web browsers, as seen by the proliferation of server-side JavaScript Server-side JavaScript refers to JavaScript that runs on the server-side. This term was coined because the language is predominantly used on the client-side, i.e. client-side JavaScript (CSJS) platforms.

In January 2009 the CommonJS project was founded with the goal of specifying a common standard library mainly for JavaScript development outside the browser.^[20]

Trademark

"JavaScript" is a trademark A trademark or trade mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or services from those of other entities of Sun Microsystems. It is used under license for technology invented and implemented by Netscape Communications and current entities such as the Mozilla Foundation The Mozilla Foundation is a non-profit organization that exists to support and provide leadership for the open source Mozilla project. The organization sets the policies that govern development, operate key infrastructure and control trademarks and other intellectual property. It owns two taxable for-profit subsidiaries: the Mozilla Corporation,.^[21]

Features

The following features are common to all conforming ECMAScript implementations, unless explicitly specified otherwise.

Imperative and structured

JavaScript supports all the structured programming Structured programming can be seen as a subset or subdiscipline of imperative programming, one of the major programming paradigms. It is most famous for removing or reducing reliance on the GOTO statement syntax in C Although C was designed for implementing system software, it is also widely used for developing portable application software (e.g., if statements, while loops, switch statements, etc.). One partial exception is scoping In computer programming, scope is an enclosing context where values and expressions are associated. Various programming languages have various types of scopes. The type of scope determines what kind of entities it can contain and how it affects them -- or semantics. Typically, scope is used to define the visibility and reach of information hiding: C-style block-level scoping is not supported (instead, JavaScript has function-level scoping). JavaScript 1.7, however, supports block-level scoping with the let keyword. Like C, JavaScript makes a distinction between expressions An expression in a programming language is a combination of values, variables, operators, and functions that are interpreted according to the particular rules of precedence and of association for a particular programming language, which computes and then produces (returns, in a stateful environment) another value. The expression is said to and statements In computer programming a statement can be thought of as the smallest standalone element of an imperative programming language. A program is formed by a sequence of one or more statements. A statement will have internal components. One syntactic difference from C is automatic semicolon insertion The syntax of JavaScript is a set of rules that defines what constitutes a valid program in the JavaScript language, in which the semicolons that terminate statements can be omitted.^[22]

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.^[23]
object based: JavaScript is almost entirely object-based. JavaScript objects are associative arrays, augmented with prototypes (see below). Object property names are string keys: obj.x = 10 and obj["x"] = 10 are equivalent, the dot notation being syntactic sugar. Properties and their values can be added, changed, or deleted at run-time. Most properties of an object (and those on its prototype inheritance chain) can be enumerated using a for...in loop. JavaScript has a small number of built-in objects such as Function and Date.
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.

Prototype-based

prototypes: JavaScript uses prototypes instead of classes for 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 constructor's prototype property determines the object used for the new object's internal prototype. JavaScript's built-in constructors, such as Array, also have prototypes that can be modified.
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 called 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". In fact, it relies on the environment to provide the ability to include/import scripts (e.g. HTML <script> elements). (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 access them through formal parameters and also through 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.

Vendor-specific extensions

JavaScript is officially managed by Mozilla Foundation, and new language features are added periodically. However, only some non-Mozilla JavaScript engines support these new features:

property getter and setter functions (also supported by WebKit, Opera,^[24] ActionScript, and Rhino)^[25]
conditional catch clauses
iterator protocol adopted from Python
shallow generators/coroutines also adopted from Python
array comprehensions and generator expressions also adopted from Python
proper block scope via new let keyword
array and object destructuring (limited form of pattern matching)
concise function expressions (function(args) expr)
ECMAScript for XML (E4X), an extension that adds native XML support to ECMAScript

Syntax and semantics

Main article: JavaScript syntax

As of 2009, the latest version of the language is JavaScript 1.8.1. It is a superset of ECMAScript (ECMA-262) Edition 3. Extensions to the language, including partial E4X (ECMA-357) support and experimental features considered for inclusion into future ECMAScript editions, are documented here.^[26]

Example - syntax and semantics

This sample code showcases various JavaScript features. The example can be executed with the following steps: (1) Copy the code to a file with extension .htm. (2) Use the Mozilla or Firefox browser to open the file.

<html>
<head><title>LCM Calculator</title></head>
<body>
<font face="Courier New" size="3">
<script type="text/javascript">
/* Finds the lowest common multiple of two numbers */
function LCMCalculator(x, y) { // constructor function
function checkInt(x) { // inner function
if (x % 1 != 0)
throw new TypeError(x + " is not an integer"); // exception throwing
return x;
}
//semicolons are optional (but beware since this may cause consecutive lines to be
//erroneously treated as a single statement)
this.a = checkInt(x)
this.b = checkInt(y)
}
// The prototype of object instances created by a constructor is
// that constructor's "prototype" property.
LCMCalculator.prototype = { // object literal
gcd : function() { // method that calculates the greatest common divisor
// Euclidean algorithm:
var a = Math.abs(this.a), b = Math.abs(this.b), t;
if (a < b) {
t = b; b = a; a = t; // swap variables
}
while (b !== 0) {
t = b;
b = a % b;
a = t;
}
// Only need to calculate gcd once, so "redefine" this method.
// (Actually not redefinition - it's defined on the instance itself,
// so that this.gcd refers to this "redefinition" instead of LCMCalculator.prototype.gcd.)
// Also, 'gcd' == "gcd", this['gcd'] == this.gcd
this['gcd'] = function() { return a; };
return a;
},
"lcm" /* can use strings here */: function() {
// Variable names don't collide with object properties, e.g. |lcm| is not |this.lcm|.
// not using |this.a * this.b| to avoid FP precision issues
var lcm = this.a / this.gcd() * this.b;
// Only need to calculate lcm once, so "redefine" this method.
this.lcm = function() { return lcm; };
return lcm;
},
toString : function() {
return "LCMCalculator: a = " + this.a + ", b = " + this.b;
}
};
// Note: Array's map() and forEach() are predefined in JavaScript 1.6.
// They are currently not available in some major JavaScript engines
// such as Internet Explorer, but are available under Firefox.
// They are used here to demonstrate JavaScript's inherent functional nature.
[[25,55],[21,56],[22,58],[28,56]].map(function(pair) { // array literal + mapping function
return new LCMCalculator(pair[0], pair[1]);
}).sort(function(a, b) { // sort with this comparative function
return a.lcm() - b.lcm();
}).forEach(function(obj) {
/* Note: print() is a JS builtin function available in Mozilla's js CLI;
* It is functionally equivalent to Java's System.out.println().
* Within a web browser, print() is a very different function
* (opens the "Print Page" dialog),
* so use something like document.write() or alert() instead.
*/
// print (obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm());
// alert (obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm());
document.write(obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm() + "<br>");
});
</script>
<noscript>
(Message from Wikipedia example) <br>
Your browser either does not support JavaScript, or you have JavaScript turned off.
</noscript>
</body>
</html>

The following output should be displayed in the browser window.

LCMCalculator: a = 28, b = 56, gcd = 28, lcm = 56
LCMCalculator: a = 21, b = 56, gcd = 7, lcm = 168
LCMCalculator: a = 25, b = 55, gcd = 5, lcm = 275
LCMCalculator: a = 22, b = 58, gcd = 2, lcm = 638

If Internet Explorer is used, the example will generate an error. Hence the example illustrates a point discussed further in the body of the article, namely, the JavaScript interpreter supported by Firefox executes source differently from the JScript interpreter supported by Internet Explorer. (See comments in the source code for details on the relevant differences for this example.)

Use in web pages

Main article: Client-side JavaScript See also: JavaScript engine and Ajax (programming)

The primary use of JavaScript is to write functions that are embedded in or included from HTML pages and that interact with the Document Object Model (DOM) of the page. Some simple examples of this usage are:

Opening or popping up a new window with programmatic control over the size, position, and attributes of the new window (e.g. whether the menus, toolbars, etc. are visible).
Validating input values of a web form to make sure that they are acceptable before being submitted to the server.
Changing images as the mouse cursor moves over them: This effect is often used to draw the user's attention to important links displayed as graphical elements.

Because JavaScript code can run locally in a user's browser (rather than on a remote server), the browser can respond to user actions quickly, making an application more responsive. Furthermore, JavaScript code can detect user actions which HTML alone cannot, such as individual keystrokes. Applications such as Gmail take advantage of this: much of the user-interface logic is written in JavaScript, and JavaScript dispatches requests for information (such as the content of an e-mail message) to the server. The wider trend of Ajax programming similarly exploits this strength.

A JavaScript engine (also known as JavaScript interpreter or JavaScript implementation) is an interpreter that interprets JavaScript source code and executes the script accordingly. The first JavaScript engine was created by Brendan Eich at Netscape Communications Corporation, for the Netscape Navigator web browser. The engine, code-named SpiderMonkey, is implemented in C. It has since been updated (in JavaScript 1.5) to conform to ECMA-262 Edition 3. The Rhino engine, created primarily by Norris Boyd (formerly of Netscape; now at Google) is a JavaScript implementation in Java. Rhino, like SpiderMonkey, is ECMA-262 Edition 3 compliant.

A web browser is by far the most common host environment for JavaScript. Web browsers typically use the public API to create "host objects" responsible for reflecting the DOM into JavaScript. The web server is another common application of the engine. A JavaScript webserver would expose host objects representing an HTTP request and response objects, which a JavaScript program could then manipulate to dynamically generate web pages.

Because JavaScript is the only language that the most popular browsers share support for, it has become a target language for many frameworks in other languages, even though JavaScript was never intended to be such a language.^[11] Despite the performance limitations inherent to its dynamic nature, the increasing speed of JavaScript engines has made the language a surprisingly feasible compilation target.

Example - use in web pages

A minimal example of a standards-conforming web page containing JavaScript (using HTML 4.01 syntax) would be the following:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head><title>simple page</title></head>
<body>
<script type="text/javascript">
document.write('Hello World!');
</script>
<noscript>
Your browser either does not support JavaScript, or you have JavaScript turned off.
</noscript>
</body>
</html>

Compatibility considerations

Main article: Web interoperability

Since JavaScript runs in widely varying environments, an important part of testing and debugging it is testing across browsers.

The DOM interfaces for manipulating web pages are not part of the ECMAScript standard, or of JavaScript itself. Officially, they are defined by a separate standardization effort by the W3C; in practice, browser implementations differ from the standards and from each other, and not all browsers execute JavaScript.

To deal with these differences, JavaScript authors can attempt to write standards-compliant code which will also be executed correctly by most browsers; failing that, they can write code that checks for the presence of certain browser features and behaves differently if they are not available.^[27] In some cases, two browsers may both implement a feature but with different behavior, and authors may find it practical to detect what browser is running and change their script's behavior to match.^[28]^[29] Programmers may also use libraries or toolkits which take browser differences into account.

Furthermore, scripts may not work for some users. For example, a user may:

use an old or rare browser with incomplete or unusual DOM support,
use a PDA or mobile phone browser which cannot execute JavaScript,
have JavaScript execution disabled as a security precaution,
use a speech browser due to, for example, a visual disability.

To support these users, web authors can try to create pages which degrade gracefully on user agents (browsers) which do not support the page's JavaScript. In particular, the page should remain usable albeit without the extra features that the JavaScript would have added.

Accessibility

Main article: Web accessibility

Assuming that the user has not disabled its execution, client-side web JavaScript should be written to enhance the experiences of visitors with visual or physical disabilities, and certainly should avoid denying information to these visitors.^[30]

Screen readers, used by the blind and partially sighted, can be JavaScript-aware and so may access and read the page DOM after the script has altered it. The HTML should be as concise, navigable and semantically rich as possible whether the scripts have run or not. JavaScript should not be totally reliant on mouse-specific events so as to deny its benefits to users who either cannot use a mouse or who choose to favor the keyboard for whatever reason. Equally, although hyperlinks and webforms can be navigated and operated from the keyboard, accessible JavaScript should not require keyboard events either. There are device-independent events such as onfocus and onchange that are preferable in most cases.^[30]

JavaScript should not be used in a way that is confusing or disorientating to any web user. For example, using script to alter or disable the normal functionality of the browser, such as by changing the way the back-button or the refresh event work, is usually best avoided. Equally, triggering events that the user may not be aware of reduces the user's sense of control as do unexpected scripted changes to the page content.^[31]

Often the process of making a complex web page as accessible as possible becomes a nontrivial problem where issues become matters of debate and opinion, and where compromises are necessary in the end. However, user agents and assistive technologies are constantly evolving and new guidelines and relevant information are continually being published on the web.^[30]

Security

JavaScript and the DOM provide the potential for malicious authors to deliver scripts to run on a client computer via the web. Browser authors contain this risk using two restrictions. First, scripts run in a sandbox in which they can only perform web-related actions, not general-purpose programming tasks like creating files. Second, scripts are constrained by the same origin policy: scripts from one web site do not have access to information such as usernames, passwords, or cookies sent to another site. Most JavaScript-related security bugs are breaches of either the same origin policy or the sandbox.

Cross-site vulnerabilities

Main articles: Cross-site scripting and Cross-site request forgery

A common JavaScript-related security problem is cross-site scripting, or XSS, a violation of the same-origin policy. XSS vulnerabilities occur when an attacker is able to cause a target web site, such as an online banking website, to include a malicious script in the webpage presented to a victim. The script in this example can then access the banking application with the privileges of the victim, potentially disclosing secret information or transferring money without the victim's authorization. A solution to XSS vulnerabilities is to use HTML escaping whenever displaying untrusted data.

Some browsers include partial protection against reflected XSS attacks, in which the attacker provides a URL including malicious script. However, even users of those browsers are vulnerable to other XSS attacks, such as those where the malicious code is stored in a database. Only correct design of Web applications on the server side can fully prevent XSS.

XSS vulnerabilities can also occur because of implementation mistakes by browser authors.^[32]

Another cross-site vulnerability is cross-site request forgery or CSRF. In CSRF, code on an attacker's site tricks the victim's browser into taking actions the user didn't intend at a target site (like transferring money at a bank). It works because, if the target site relies only on cookies to authenticate requests, then requests initiated by code on the attacker's site will carry the same legitimate login credentials as requests initiated by the user. In general, the solution to CSRF is to require an authentication value in a hidden form field, and not only in the cookies, to authenticate any request that might have lasting effects. Checking the HTTP Referrer header can also help.

"JavaScript hijacking" is a type of CSRF attack in which a <script> tag on an attacker's site exploits a page on the victim's site that returns private information as JSON or JavaScript. Possible solutions include requiring an authentication token in the POST and GET parameters for any response that returns private JSON (even if it has no side effects); using POST and never GET for requests that return private JSON; and modifying the response so that it can't be used via a <script> tag (by, for example, wrapping the JSON in a JavaScript comment).

Misplaced trust in the client

Client-server applications, whether they involve JavaScript or not, must recognize that untrusted clients may be under the control of attackers. Thus any secret embedded in JavaScript could be extracted by a determined adversary, and the application author can't assume that his JavaScript runs as intended, or at all. Some implications:

Web site authors cannot perfectly conceal how their JavaScript operates, because the code is sent to the client, and obfuscated code can be reverse-engineered.
JavaScript form validation only provides convenience for users, not security. If a site verifies that the user agreed to its terms of service, or filters invalid characters out of fields that should only contain numbers, it must do so on the server, not only the client.
Scripts can be selectively disabled, so JavaScript can't be relied on to prevent operations such as "save image".^[33]
It would be extremely bad practice to embed a password in JavaScript (where it can be extracted by an attacker), then have JavaScript verify a user's password and pass "password_ok=1" back to the server (since the "password_ok=1" response is easy to forge).^[34]

Browser and plugin coding errors

JavaScript provides an interface to a wide range of browser capabilities, some of which may have flaws such as buffer overflows. These flaws can allow attackers to write scripts which would run any code they wish on the user's system.

These flaws have affected major browsers including Firefox,^[35] Internet Explorer,^[36] and Safari.^[37]

Plugins, such as video players, Adobe Flash, and the wide range of ActiveX controls enabled by default in Microsoft Internet Explorer, may also have flaws exploitable via JavaScript, and such flaws have been exploited in the past.^[38]^[39]

In Windows Vista, Microsoft has attempted to contain the risks of bugs such as buffer overflows by running the Internet Explorer process with limited privileges.^[40] Google Chrome similarly limits page renderers to an operating-system-enforced "sandbox."

Sandbox implementation errors

Web browsers are capable of running JavaScript outside of the sandbox, with the privileges necessary to, for example, create or delete files. Of course, such privileges aren't meant to be granted to code from the web.

Incorrectly granting privileges to JavaScript from the web has played a role in vulnerabilities in both Internet Explorer^[41] and Firefox.^[42] In Windows XP Service Pack 2, Microsoft demoted JScript's privileges in Internet Explorer.^[43]

Microsoft Windows allows JavaScript source files on a computer's hard drive to be launched as general-purpose, non-sandboxed programs. This makes JavaScript (like VBScript) a theoretically viable vector for a Trojan horse, although JavaScript Trojan horses are uncommon in practice.^[44] (See Windows Script Host.)

Uses outside web pages

In addition to web browsers and servers, JavaScript interpreters are embedded in a number of tools. Each of these applications provides its own object model which provides access to the host environment, with the core JavaScript language remaining mostly the same in each application.

Embedded scripting language

Apple's Dashboard Widgets, Microsoft's Gadgets, Yahoo! Widgets, Google Desktop Gadgets, Serence Klipfolio are implemented using JavaScript.
Adobe's Acrobat and Adobe Reader (formerly Acrobat Reader) support JavaScript in PDF files.^[45]
Tools in the Adobe Creative Suite, including Photoshop, Illustrator, Dreamweaver and InDesign, allow scripting through JavaScript.
OpenOffice.org office application suite allows for JavaScript as one of its scripting languages.
The interactive music signal processing software Max/MSP released by Cycling '74, offers a JavaScript model of its environment for use by developers. It allows much more precise control than the default GUI-centric programming model.
ECMAScript was included in the VRML97 standard for scripting nodes of VRML scene description files.
Some high-end Philips universal remote panels, including TSU9600 and TSU9400, can be scripted using a JavaScript-based tool called ProntoScript.^[46]
Sphere is an open source and cross platform computer program designed primarily to make role-playing games that use JavaScript as a scripting language.
The open-source Re-Animator framework allows developing 2D sprite-based games using JavaScript and XML.
Methabot is a web crawler that uses JavaScript as scripting language for custom filetype parsers and data extraction using E4X.
The game engine Unity supports three scripting languages: JavaScript, C#, and Boo.^[47]
DX Studio (3D engine) uses the SpiderMonkey implementation of JavaScript for game and simulation logic.^[48]
Maxwell Render provides an ECMA standard based scripting engine for tasks automation.^[49]
Google Docs Spreadsheet has a script editor which allows users to create custom formulas, automate repetitive tasks and also interact with other Google products such as Gmail.^[50]

Scripting engine

Microsoft's Active Scripting technology supports the JavaScript-compatible JScript as a scripting language used in HTML Applications.
The Java programming language, in version SE 6 (JDK 1.6), introduced the javax.script package, including a JavaScript implementation based on Mozilla Rhino. Thus, Java applications can host scripts that access the application's variables and objects, much like web browsers host scripts that access the browser's Document Object Model (DOM) for a webpage.^[51]^[52]
The Qt C++ toolkit includes a QtScript module to interpret JavaScript, analogous to javax.script.^[53]
Late Night Software's JavaScript OSA (aka JavaScript for OSA, or JSOSA), is a freeware alternative to AppleScript for Mac OS X. It is based on the Mozilla 1.5 JavaScript implementation, with the addition of a MacOS object for interaction with the operating system and third-party applications.^[54]

Application platform

ActionScript, the programming language used in Adobe Flash, is another implementation of the ECMAScript standard.
The Mozilla platform, which underlies Thunderbird, Firefox and some other web browsers, uses JavaScript to implement the graphical user interface (GUI) of its various products.
Adobe Integrated Runtime is a JavaScript runtime that allows developers to create desktop applications.
webOS uses the WebKit implementation of JavaScript as a part of its application framework.
CA, Inc.'s AutoShell cross-application scripting environment is built on JavaScript/SpiderMonkey with preprocessor like extensions for command definitions and custom classes for various system related tasks like file i/o, operation system command invocation and redirection and COM scripting.
GNOME Shell, the shell for the GNOME 3 desktop environment.^[55] The Seed,^[56] Gjs (from Gnome) and Kjsembed^[57] (from KDE) packages are aimed to utilize that needs.

Development tools

Within JavaScript, access to a debugger becomes invaluable when developing large, non-trivial programs. Because there can be implementation differences between the various browsers (particularly within the Document Object Model) it is useful to have access to a debugger for each of the browsers that a web application targets.^[58]

Script debuggers are available for Internet Explorer, Firefox, Safari, Google Chrome, and Opera.^[59]

Three debuggers are available for Internet Explorer: Microsoft Visual Studio is the richest of the three, closely followed by Microsoft Script Editor (a component of Microsoft Office),^[60] and finally the free Microsoft Script Debugger which is far more basic than the other two. The free Microsoft Visual Web Developer Express provides a limited version of the JavaScript debugging functionality in Microsoft Visual Studio.

Web applications within Firefox can be debugged using the Firebug add-on, or the older Venkman debugger. Firefox also has a simpler built-in Error Console, which logs and evaluates JavaScript. It also logs CSS errors and warnings.

Opera includes a set of tools called DragonFly.^[61]

WebKit's Web Inspector includes a JavaScript debugger^[62] in Apple's Safari.

Some debugging aids are themselves written in JavaScript and built to run on the Web. An example is the program JSLint, developed by Douglas Crockford, currently senior JavaScript architect at Yahoo! who has written extensively on the language. JSLint scans JavaScript code for conformance to a set of standards and guidelines. Web development bookmarklets and Firebug Lite provide variations on the idea of the cross-browser JavaScript console.

Versions

Version	Release date	Equivalent to	Netscape Navigator	Mozilla Firefox	Internet Explorer	Opera	Safari	Google Chrome
1.0	March 1996		2.0		3.0
1.1	August 1996		3.0
1.2	June 1997		4.0-4.05
1.3	October 1998	ECMA-262 1^st edition / ECMA-262 2^nd edition	4.06-4.7x		4.0
1.4			Netscape Server
1.5	November 2000	ECMA-262 3^rd edition	6.0	1.0	5.5 (JScript 5.5), 6 (JScript 5.6), 7 (JScript 5.7), 8 (JScript 5.8)	6.0, 7.0, 8.0, 9.0, 10.0	3.0, 3.1, 3.2, 4.0	1.0
1.6	November 2005	1.5 + Array extras + Array and String generics + E4X		1.5
1.7	October 2006	1.6 + Pythonic generators + Iterators + let		2.0
1.8	June 2008	1.7 + Generator expressions + Expression closures		3.0
1.8.1		1.8 + Native JSON support + Minor Updates		3.5
1.8.2		1.8.1 + Minor updates		3.6
1.9		1.8.1 + ECMAScript 5 Compliance		4

^[63]

Related languages and features

Since the acceptance of JavaScript as a popular language, several languages and features have developed from it.

Objective-J is a strict superset of JavaScript that adds traditional inheritance and Smalltalk/Objective-C style dynamic dispatch and optional pseudo-static typing to pure JavaScript.

TIScript is a superset of JavaScript that adds classes, namespaces and lambda expressions.

JSON, or JavaScript Object Notation, is a general-purpose data interchange format that is defined as a subset of JavaScript.

Mozilla browsers currently support LiveConnect, a feature that allows JavaScript and Java to intercommunicate on the web. However, Mozilla-specific support for LiveConnect is scheduled to be phased out in the future in favor of passing on the LiveConnect handling via NPAPI to the Java 1.6+ plug-in (not yet supported on the Mac as of March 2010).^[64]

JavaScript and Java

A common misconception is that JavaScript is similar or closely related to Java. It is true that both have a C-like syntax, the C language being their most immediate common ancestor language. They are both object-oriented, typically sandboxed (when used inside a browser), and are widely used in client-side Web applications. In addition, JavaScript was designed with Java's syntax and standard library in mind. In particular, all Java keywords are reserved in JavaScript, JavaScript's standard library follows Java's naming conventions, and JavaScript's Math and Date objects are based on classes from Java 1.0.^[16]

But the similarities end there. Java has static typing; JavaScript's typing is dynamic (meaning a variable can hold an object of any type and cannot be restricted). Java is loaded from compiled bytecode; JavaScript is loaded as human-readable source code. Java's objects are class-based; JavaScript's are prototype-based. JavaScript also has many functional features based on the Self language.

References

^ Firefox 3.6 supports JavaScript 1.8.2
^ Mozilla.org
^ RFC 4329
^ "System-Declared Uniform Type Identifiers". Mac OS X Reference Library. Apple Inc.. http://developer.apple.com/mac/library/documentation/Miscellaneous/Reference/UTIRef/Articles/System-DeclaredUniformTypeIdentifiers.html. Retrieved 2010-03-05.
^ "ECMAScript Language Specification". http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf.
^ Douglas Crockford on Functional JavaScript (2:49): "[JavaScript] is also coincidentally the world's most popular functional programming language. JavaScript is and has always been, at least since [version] 1.2, a functional programming language."
^ The Little JavaScripter shows the relationship with Scheme in more detail.
^ "ECMAScript Language Overview" (PDF). 2007-10-23. pp. 4. http://www.ecmascript.org/es4/spec/overview.pdf. Retrieved 2009-05-03.
^ wikinews:Wikinews:Story preparation/Interview with Robert Cailliau
^ Krill, Paul (2008-06-23). "JavaScript creator ponders past, future". InfoWorld. http://www.infoworld.com/article/08/06/23/eich-javascript-interview_1.html. Retrieved 2009-05-19.
^ ^a ^b Hamilton, Naomi (2008-06-31). "The A-Z of Programming Languages: JavaScript". computerworld.com.au. http://www.computerworld.com.au/article/255293/-z_programming_languages_javascript.
^ Press release announcing JavaScript, "Netscape and Sun announce Javascript(TM)", PR Newswire, Dec 4, 1995
^ "TechVision: Innovators of the Net: Brendan Eich and JavaScript". Web.archive.org. Archived from the original on 2008-02-08. http://web.archive.org/web/20080208124612/http://wp.netscape.com/comprod/columns/techvision/innovators_be.html. Retrieved 2010-06-14.
^ "Programming languages used on the Internet and the World Wide Web (WWW)". Webdevelopersnotes.com. http://www.webdevelopersnotes.com/basics/languages_on_the_internet.php3. Retrieved 2009-05-19.
^ "O'Reilly - Safari Books Online - 0596101996 - JavaScript: The Definitive Guide, 5th Edition". Safari.oreilly.com. http://safari.oreilly.com/0596101996/jscript5-CHP-1. Retrieved 2009-05-19.
^ ^a ^b "Brendan's Roadmap Updates: Popularity". Weblogs.mozillazine.org. http://weblogs.mozillazine.org/roadmap/archives/2008/04/popularity.html. Retrieved 2009-05-19.
^ Microsoft JScript Features - Non-ECMA
^ ECMAScript 3rd Edition specification
^ "JavaScript: The World's Most Misunderstood Programming Language". Crockford.com. http://www.crockford.com/javascript/javascript.html. Retrieved 2009-05-19.
^ Kris Kowal (1 December 2009). "CommonJS effort sets JavaScript on path for world domination". Ars Technica. Condé Nast Publications. http://arstechnica.com/web/news/2009/12/commonjs-effort-sets-javascript-on-path-for-world-domination.ars. Retrieved 18 April 2010.
^ "Sun Trademarks". Sun Microsystems. http://www.sun.com/suntrademarks/. Retrieved 2007-11-08.
^ Flanagan, David (2006). JavaScript: The definitive Guide. p. 16. ISBN 978-0-596-10199-2. "Omitting semicolons is not a good programming practice; you should get into the habit of inserting them."
^ Flanagan, David (2006). JavaScript: The Definitive Guide. O'Reilly Media. pp. 176–178. ISBN 0596101996.
^ Robert Nyman, Getters And Setters With JavaScript – Code Samples And Demos, published 29 May 2009, accessed 2 January 2010.
^ John Resig, JavaScript Getters and Setters, 18 July 2007, accessed 2 January 2010
^ "About - MDC". Developer.mozilla.org. 2008-08-31. https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference:About. Retrieved 2009-05-19.
^ Peter-Paul Koch, Object detection
^ Peter-Paul Koch, Mission Impossible - mouse position
^ Peter-Paul Koch, Browser detect
^ ^a ^b ^c Flanagan, David (2006). JavaScript: The definitive guide. O'Reilly. pp. 262–263. ISBN 978-0-596-10199-2.
^ "Creating Accessible JavaScript". WebAIM. http://www.webaim.org/techniques/javascript/. Retrieved 8 June 2010.
^ MozillaZine, Mozilla Cross-Site Scripting Vulnerability Reported and Fixed
^ Right-click “protection”? Forget about it. 2008-06-17. ISSN 1797-1993. http://blog.anta.net/2008/06/17/right-click-%e2%80%9cprotection%e2%80%9d-forget-about-it/. Retrieved 2008-06-17.
^ For an example of this bad practice, see Javascript.internet.com
^ Mozilla Corporation, Buffer overflow in crypto.signText()
^ Paul Festa, CNet, Buffer-overflow bug in IE
^ SecurityTracker.com, Apple Safari JavaScript Buffer Overflow Lets Remote Users Execute Arbitrary Code and HTTP Redirect Bug Lets Remote Users Access Files
^ SecurityFocus, Microsoft WebViewFolderIcon ActiveX Control Buffer Overflow Vulnerability
^ Fusion Authority, Macromedia Flash ActiveX Buffer Overflow
^ Mike Friedman, Protected Mode in Vista IE7
^ US CERT, Vulnerability Note VU#713878: Microsoft Internet Explorer does not properly validate source of redirected frame
^ Mozilla Foundation, Mozilla Foundation Security Advisory 2005-41: Privilege escalation via DOM property overrides
^ Microsoft Corporation, Changes to Functionality in Microsoft Windows XP Service Pack 2: Part 5: Enhanced Browsing Security
^ For one example of a rare JavaScript Trojan Horse, see Symantec Corporation, JS.Seeker.K
^ "JavaScript for Acrobat". http://www.adobe.com/devnet/acrobat/javascript.html. Retrieved 2009-08-18.
^ Koninklijke Philips Electronics NV
^ "Best Of All Worlds". unity3d.com. http://unity3d.com/unity/features/scripting. Retrieved 2009-09-12.
^ "Technical Specification". dxstudio.com. http://www.dxstudio.com/features_tech.aspx. Retrieved 2009-10-20.
^ THINK! The Maxwell Render Resourcer Center, Scripting References
^ Google Apps Script, Welcome to Google Apps Script
^ "javax.script release notes". Java.sun.com. http://java.sun.com/javase/6/webnotes/index.html#scripting. Retrieved 2009-05-19.
^ Flanagan 5th Edition, Pp 214 et seq
^ Nokia Corporation, QtScript Module
^ Open Scripting Architecture
^ "Behind the Scenes with Owen Taylor". The GNOME Journal. http://gnomejournal.org/article/74/behind-the-scenes-with-owen-taylor. Retrieved 2010-01-23.
^ Devel.akbkhome.com
^ Xmelegance.org
^ "Advanced Debugging With JavaScript". alistapart.com. 2009-02-03. http://www.alistapart.com/articles/advanced-debugging-with-javascript/. Retrieved 2010-05-28.
^ "The JavaScript Debugging Console". javascript.about.com. 2010-05-28. http://javascript.about.com/od/problemsolving/ig/JavaScript-Debugging/. Retrieved 2010-05-28.
^ JScript development in Microsoft Office 11 (MS InfoPath 2003)
^ "Opera DragonFly". Opera Software. http://www.opera.com/dragonfly/.
^ "Introducing Drosera - Surfin' Safari". Webkit.org. 2006-06-28. http://webkit.org/blog/61/introducing-drosera/. Retrieved 2009-05-19.
^ John Resig. "Versions of JavaScript". Ejohn.org. http://ejohn.org/blog/versions-of-javascript. Retrieved 2009-05-19.
^ Java.sun.com

External links

Wikibooks has a book on the topic of JavaScript

Douglas Crockford's video lectures on JavaScript
FAQ for Usenet's comp.lang.javascript
JavaScript at the Open Directory Project
Mozilla Developer Center
- Mozilla's Official Documentation on JavaScript
- References for Core JavaScript versions: 1.5+
- New in JavaScript: 1.5, 1.6, 1.7, 1.8, 1.8.1
- List of JavaScript releases: versions 1.5+
- Re-Introduction to JavaScript
Programming languages implemented in JavaScript

ECMAScript

Dialects

ActionScript · Caja · JavaScript (engines) · JScript · JavaScript OSA · JScript .NET · Objective-J · QtScript · WMLScript

Engines · Comparison

Carakan · Futhark · InScript · JavaScriptCore (SquirrelFish) · JScript · KJS · Linear B · Narcissus · QtScript · Rhino · SpiderMonkey (TraceMonkey) · Tamarin · V8 · Chakra

Frameworks & libraries

JavaScript (comparison)

Client-side (List of Ajax frameworks)	Ample SDK · Clean AJAX · CougarXML · Dojo · Echo · Ext · Google Web Toolkit · jQuery · Lively Kernel · midori · MochiKit · MooTools · OpenLink AJAX · Prototype · Pyjamas · qooxdoo · Rialto · Rico · script.aculo.us · SmartClient · SproutCore · Spry · Yahoo! UI Library

Server-side (comparison)	AppJet · Jaxer · Node.js

Libraries (List)	PDFObject · SWFObject · SWFAddress · SWFFit

ActionScript

PureMVC

Multiple Implementations

Cappuccino (JavaScript / Objective-J)

People

Brendan Eich · Douglas Crockford · John Resig

Other

DHTML · Ecma International · JSAN · JSDoc · JSLint · JSON · JSSS · SunSpider

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What is the sample JavaScript code for a web page to be scroll down automatically?
Q. What is the sample JavaScript code for a web page to be scroll down automatically? (Or when click on vertical scroll bar). Please provide code for similar functionality. Thanks.
Asked by Shaggy S - Mon Dec 29 12:44:28 2008 - - 1 Answers - 0 Comments

A. window.scrollBy(0,0); First 0 is your x, or width, scroll, second 0 is your y, or height, scroll, in characters or rows. This will actually scroll. window.scroll(0,0); This does the same thing, only it jumps to that part of the page instead of scrolling, so the animated effect of scrolling does not occur. Scroll by a button: function scrollDown(){ window.scroll(0,10); } function scrollStop(){ clearInterval(scolling); } In the button, set an interval and a clear:
Answered by Rockstar - Mon Dec 29 13:14:08 2008

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