From Wikipedia, the free encyclopedia
Not to be confused with , , or .
It has been suggested that
into this article. () Proposed since April 2015.
JavaScript () is a , , , and
programming language. It has been standardized in the
language specification. Alongside
and , it is one of the three essential technologies of the majority of
employ it and it is supported by all modern
without . JavaScript is
with , making it a
language, supporting , , and
programming styles. It has an
for working with text, , dates and , but does not include any , such as networking, storage or graphics facilities, relying for these upon the host environment in which it is embedded.
Despite some naming, , and
similarities, JavaScript and
are otherwise unrelated and have very different . The syntax of JavaScript is actually derived from , while the semantics and design are influenced by the
programming languages.
JavaScript is also used in environments that are not web-based, such as
documents, , and . Newer and faster JavaScript
(VMs) and platforms built upon them have also increased the popularity of JavaScript for server-side . On the client side, JavaScript has been traditionally implemented as an
language, but more recent browsers perform . It is also used in game development, the creation of desktop and mobile applications, and server-side network programming with runtime environments such as .
JavaScript was originally developed in 10 days in May 1995 by , while he was working for . Indeed, while competing with
for user adoption of web technologies and platforms, Netscape considered their client-server offering a distributed OS with a portable version of ' Java providing an environment in which
could be run.[] Because Java was a competitor of
and aimed at professional programmers, Netscape also wanted a lightweight
that would complement Java by appealing to nonprofessional programmers, like Microsoft's Visual Basic (see ).
Although it was developed under the name Mocha, the language was officially called LiveScript when it first shipped in beta releases of Netscape Navigator 2.0 in September 1995, but it was renamed JavaScript when it was deployed in the Netscape browser version 2.0B3.
The change of name from LiveScript to JavaScript roughly coincided with Netscape adding support for Java technology in its
web browser. The final choice of name caused confusion, giving the impression that the language was a spin-off of the , and the choice has been characterized as a marketing ploy by Netscape to give JavaScript the cachet of what was then the hot new web programming language.
There is a common misconception that the JavaScript language was influenced by an earlier web page scripting language developed by
named C--, not to be confused with the later
created in 1997. Brendan Eich, however, had never heard of C-- before he created LiveScript. Nombas did pitch their embedded web page scripting to Netscape, though web page scripting was not a new concept, as shown by . Nombas later switched to offering JavaScript instead of C-- in their ScriptEase product and was part of the TC39 group that standardized .
Netscape introduced an implementation of the language for
in December, 1995, soon after releasing JavaScript for browsers. Since the mid-2000s, there has been a resurgence of , such as Node.js.
script technologies including
were released in 1996. JScript, a port of Netscape's JavaScript, was released on July 16, 1996 and was part of , as well as being available server-side in . IE3 also included Microsoft's first support for
and various extensions to HTML, but in each case the implementation was noticeably different to that found in
at the time. These differences made it difficult for designers and programmers to make a single website work well in both browsers leading to the use of 'best viewed in Netscape' and 'best viewed in Internet Explorer' logos that characterised these early years of the . JavaScript began to acquire a reputation for being one of the roadblocks to a cross-platform and standards-driven web. Some developers took on the difficult task of trying to make their sites work in both major browsers, but many could not afford the time. With the release of , Microsoft introduced the concept of , but the differences in language implementations and the different and proprietary
remained, and were obstacles to widespread take-up of JavaScript on the web.
In November 1996, Netscape announced that it had submitted JavaScript to
for consideration as an industry standard, and subsequent work resulted in the standardized version named . In June 1997,
published the first edition of the
. In June 1998, some modifications were made to adapt it to the ISO/IEC-16262 standard, and the second edition was released. The third edition of
was published on December 1999.
Development of the fourth edition of the ECMAScript standard was never completed. The fifth edition was released in December 2009. The current edition of the ECMAScript standard is 6, released in June 2015.
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 consisted of Web authors and other such "amateurs", among other reasons. The advent of
returned JavaScript to the spotlight and brought more professional programming attention. The result was a proliferation of comprehensive , improved JavaScript programming practices, and increased usage of JavaScript outside Web browsers, as seen by the proliferation of
platforms.
In January 2009, the
project was founded with the goal of specifying a common standard library mainly for JavaScript development outside the browser.
With the rise of the single-page web app and JavaScript-heavy sites, it is increasingly being used as a compile target for
and . In particular,
and highly optimized , in tandem with
that is friendly to
like , have enabled
programs to be compiled into JavaScript and execute at near-native speeds, causing JavaScript to be considered the "assembly language of the web", according to its creator and others.
"JavaScript" is a
of . It is used under license for technology invented and implemented by Netscape Communications and current entities such as the .
The following features are common to all conforming ECMAScript implementations, unless explicitly specified otherwise.
JavaScript supports much of the
syntax from
(e.g., if statements, while loops, switch statements, do while loops, etc.). One partial exception is : JavaScript originally had only
with var. ECMAScript 2015 adds a let keyword for block scoping, meaning JavaScript now has both function and block scoping. Like C, JavaScript makes a distinction between
and . One syntactic difference from C is , which allows the semicolons that would normally terminate statements to be omitted.
Dynamic typing
As in most ,
are associated with , not with . For example, a variable x could be bound to a number, then later rebound to a . JavaScript supports various ways to test the type of an object, including .
Object-based
JavaScript is almost entirely . JavaScript
are , augmented with prototypes (see below). Object property names are string keys. They support two equivalent syntaxes: dot notation (obj.x = 10) and bracket notation (obj['x'] = 10). 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
function that can execute statements provided as strings at run-time.
First-class functions
they are objects themselves. As such, they have properties and methods, such as .call() and .bind(). A nested function is a function defined within another function. It is created each time the outer function is invoked. In addition, each created function forms a : the
of the outer function, including any constants, local variables and argument values, becomes part of the internal state of each inner function object, even after execution of the outer function concludes. JavaScript also supports .
Prototypes
JavaScript uses
where many other object-oriented languages use
for . 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 will create an instance of a prototype, inheriting properties and methods from the constructor (including properties from the Object prototype). ECMAScript 5 offers the Object.create method, allowing explicit creation of an instance without automatically inheriting from the Object prototype (older environments can assign the prototype to null). The constructor's prototype property determines the object used for the new object's internal prototype. New methods can be added by modifying the prototype of the function used as a constructor. JavaScript's built-in constructors, such as Array or Object, also have prototypes that can be modified. While it is possible to modify the Object prototype, it is generally considered bad practice because most objects in JavaScript will inherit methods and properties from the Object prototype and they may not expect the prototype to be modified.
Functions as methods
Unlike many object-oriented languages, there is no distinction between a function definition and a
definition. Rather, the distinction occurs dur 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.
JavaScript is a .
Functions as Roles (Traits and Mixins)
JavaScript natively supports various function-based implementations of
patterns like
and . Such a function defines additional behavior by at least one method bound to the this keyword within its function body. A Role then has to be delegated explicitly via call or apply to objects that need to feature additional behavior that is not shared via the prototype chain.
Object Composition and Inheritance
Whereas explicit function-based delegation does cover
in JavaScript, implicit delegation already happens every time the prototype chain is walked in order to, e.g., find a method that might be related to but is not directly owned by an object. Once the method is found it gets called within this object's context. Thus
in JavaScript is covered by a delegation automatism that is bound to the prototype property of constructor functions.
Run-time environment
JavaScript typically relies on a run-time environment (e.g., a ) to provide objects and methods by which scripts can interact with the environment (e.g., a webpage DOM). It also relies on the run-time environment to provide the ability to include/import scripts (e.g.,
&script& elements). This is not a language feature per se, but it is common in most JavaScript implementations.
JavaScript processes
one at a time. Upon loading a new message, JavaScript calls a
associated with that message, which creates a
frame (the function's
and ). The call stack shrinks and grows based on the function's needs. Upon function completion, when the stack is empty, JavaScript proceeds to the next message in the queue. This is called the , described as "run to completion" because each message is fully processed before the next message is considered. However, the language's
describes the event loop as : program
is performed using
and . This means, for instance, that JavaScript can process a mouse click while waiting for a database query to return information.
Variadic functions
An indefinite number of parameters can be passed to a function. The function can access them through
and also through the local arguments object.
can also be created by using the
Array and object literals
Like many scripting languages, arrays and objects ( in other languages) can each be created with a succinct shortcut syntax. In fact, these
form the basis of the
data format.
Regular expressions
JavaScript also supports
in a manner similar to , which provide a concise and powerful syntax for text manipulation that is more sophisticated than the built-in string functions.
JavaScript is officially managed by , and new language features are added periodically. However, only some
support these new features:
property getter and setter functions (supported by WebKit, Gecko, Opera, ActionScript, and Rhino)
conditional catch clauses
iterator protocol (adopted from )
shallow - (adopted from Python)
and generator expressions (adopted from Python)
proper block scope via the let keyword
array and object destructuring (limited form of )
concise function expressions (function(args) expr)
(E4X), an extension that adds native XML support to ECMAScript (unsupported in Firefox since version 21)
Main article:
in JavaScript can be defined using the var keyword:
var x; // defines the variable x, the special value “undefined” (not to be confused with an undefined value) is assigned to it by default
var y = 2; // defines the variable y and assigns the value of 2 to it
in the example above, both of which were preceded with two .
There is no built-in
functionality in JavaS the run-time environment provides that. The ECMAScript specification in edition 5.1 mentions:
... indeed, there are no provisions in this specification for input of external data or output of computed results.
However, most runtime environments have a console object that can be used to print output. Here is a minimalist :
console.log("Hello World!");
function factorial(n) {
if (n == 0) {
return n * factorial(n - 1);
(or lambda) syntax and
var displayClosure = function() {
var count = 0;
return function () {
return ++count;
var inc = displayClosure();
inc(); // returns 1
inc(); // returns 2
inc(); // returns 3
demonstration (arguments is a special ).
var sum = function() {
var i, x = 0;
for (i = 0; i & arguments.length; ++i) {
x += arguments[i];
sum(1, 2, 3); // returns 6
allow functions to pass around variables under their own closures.
var getValue = (function(v) {
return function() {return v;};
getValue(); // 1
This sample code displays various JavaScript features.
/* Finds the lowest common multiple (LCM) of two numbers */
function LCMCalculator(x, y) { // constructor function
var checkInt = function (x) { // inner function
if (x % 1 !== 0) {
throw new TypeError(x + " is not an integer"); // throw an exception
this.a = checkInt(x)
semicolons
are optional, a newline is enough
this.b = checkInt(y);
// The prototype of object instances created by a constructor is
// that constructor's "prototype" property.
LCMCalculator.prototype = { // object literal
constructor: LCMCalculator, // when reassigning a prototype, set the constructor property appropriately
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) {
// swap variables
while (b !== 0) {
b = a % b;
// 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.
// Note that this leads to a wrong result if the LCMCalculator object members "a" and/or "b" are altered afterwards.)
// Also, 'gcd' === "gcd", this['gcd'] === this.gcd
this['gcd'] = function () {
// Object property names can be specified by strings delimited by double (") or single (') quotes.
lcm : 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;
// Define gen this implementation only works for Web browsers
function output(x) {
document.body.appendChild(document.createTextNode(x));
document.body.appendChild(document.createElement('br'));
// Note: Array's map() and forEach() are defined in JavaScript 1.6.
// 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) {
output(obj + ", gcd = " + obj.gcd() + ", lcm = " + obj.lcm());
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
The most common use of JavaScript is to add client-side behavior to
pages, a.k.a.
(DHTML). Scripts are embedded in or included from
pages and interact with the
(DOM) of the page. Some simple examples of this usage are:
Loading new page content or submitting data to the server via
without reloading the page (for example, a social network might allow the user to post status updates without leaving the page)
Animation of page elements, fading them in and out, resizing them, moving them, etc.
Interactive content, for example games, and playing audio and video
input values of a
to make sure that they are acceptable before being submitted to the server.
Transmitting information about the user's reading habits and browsing activities to various websites. Web pages frequently do this for , ,
or other purposes.
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 that HTML alone cannot, such as individual keystrokes. Applications such as
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
programming similarly exploits this strength.
(also known as JavaScript interpreter or JavaScript implementation) is an
that interprets JavaScript
and executes the
accordingly. The first JavaScript engine was created by
at , for the
. The engine, code-named , is implemented in . It has since been updated (in JavaScript 1.5) to conform to ECMA-262 Edition 3. The
engine, created primarily by Norris Boyd (formerly of N now at Google) is a JavaScript implementation in . 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 create "host objects" to represent the
(DOM) in JavaScript. The
is another common host environment. A
would typically expose host objects representing
request and response objects, which a JavaScript program could then interrogate and manipulate to dynamically generate web pages.
Because JavaScript is the only language that the most popular browsers share support for, it has become a
for many frameworks in other languages, even though JavaScript was never intended to be such a language. Despite the performance limitations inherent to its dynamic nature, the increasing speed of JavaScript engines has made the language a surprisingly feasible compilation target.
Below is a minimal example of a standards-conforming web page containing JavaScript (using
syntax) and the :
&!DOCTYPE html&
&meta charset="utf-8"&
&title&Minimal Example&/title&
&h1 id="header"&This is JavaScript&/h1&
document.body.appendChild(document.createTextNode('Hello World!'));
var h1 = document.getElementById('header'); // holds a reference to the &h1& tag
h1 = document.getElementsByTagName('h1')[0]; // accessing the same &h1& element
&noscript&Your browser either does not support JavaScript, or has it turned off.&/noscript&
Main article:
Because JavaScript runs in widely varying environments, an important part of testing and debugging is to test and verify that the JavaScript works across multiple browsers.
The DOM interfaces for manipulating web pages are not part of the ECMAScript standard, or of JavaScript itself. Officially, the DOM interfaces are defined by a separate standardiz 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 that will also be executed correc failing that, they can write code that checks for the presence of certain browser features and behaves differently if they are not available. 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. Programmers may also use libraries or toolkits that 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,
browser that 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 that
on user agents (browsers) that 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. An alternative approach that many find preferable is to first author content using basic technologies that work in all browsers, then enhance the content for users that have JavaScript enabled. This is known as .
Main article:
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 , and certainly should avoid denying information to these visitors.
, used by the , 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
as possible whether the scripts have run or not. JavaScript should not be totally reliant on
specific events because a user may be physically unable to use these input devices. For this reason, device-agnostic events such as onfocus and onchange are preferable to device-centric events such as onmouseover and onkeypress in most cases.
JavaScript should not be used in a way that is confusing or disorienting 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" or "refresh" buttons 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.
Often the process of making a complex web page as accessible as possible becomes a
problem where issues become matters of debate and opinion, and where compromises are necessary in the end. However, user agents and
are constantly evolving and new guidelines and relevant information are continually being published on the Web.
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
in which they can only perform Web-related actions, not general-purpose programming tasks like creating files. Second, scripts are constrained by the : 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.
There are subsets of general JavaScript — ADsafe, Secure ECMA Script (SES) — that provide greater level of security, especially on code created by third parties (such as advertisements).
is the main intended method of ensuring that only trusted code is executed on a web page.
Main articles:
A common JavaScript-related security problem is , or XSS, a violation of the . 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.
Another cross-site vulnerability is
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 such as JSON or JavaScript. Possible solutions include:
requiring an authentication token in the
parameters for any response that returns private information
Developers of client-server applications must recognize that untrusted clients may be under the control of attackers. The application author cannot assume that his JavaScript code will run as intended (or at all) because any secret embedded in the code could be extracted by a determined adversary. Some implications are:
Web site authors cannot perfectly conceal how their JavaScript operates because the raw source code must be sent to the client. The code can be , but obfuscation 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 right-clicking on an image to save it.
It is extremely bad practice to embed sensitive information such as passwords in JavaScript because it can be extracted by an attacker.
JavaScript provides an interface to a wide range of browser capabilities, some of which may have flaws such as . These flaws can allow attackers to write scripts that would run any code they wish on the user's system. This code is not by any means limited to another JavaScript application. For example, a buffer overrun exploit can allow an attacker to gain access to the operating system's API with superuser privileges.
These flaws have affected major browsers including Firefox, Internet Explorer, and Safari.
Plugins, such as video players, , and the wide range of
controls enabled by default in Microsoft Internet Explorer, may also have flaws exploitable via JavaScript (such flaws have been exploited in the past).
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.
similarly confines its page renderers to their own "sandbox".
Web browsers are capable of running JavaScript outside 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 and Firefox. In Windows XP Service Pack 2, Microsoft demoted JScript's privileges in Internet Explorer.
allows JavaScript source files on a computer's hard drive to be launched as general-purpose, non-sandboxed programs (see: ). This makes JavaScript (like ) a theoretically viable vector for a , although JavaScript Trojan horses are uncommon in practice.
In addition to web browsers and servers, JavaScript interpreters are embedded in a number of tools. Each of these applications provides its own
that provides access to the host environment. The core JavaScript language remains mostly the same in each application.
extensions, 's extensions, Apple's
extensions, Apple's , Microsoft's , , , and
are implemented using JavaScript.
database accepts queries written in JavaScript.
are the core components of : a
for creating Web applications using just JavaScript.
support JavaScript in
Tools in the , including , , , and , allow scripting through JavaScript.
, an office application suite, as well as its popular fork , allows JavaScript to be used as a scripting language.
The interactive music signal processing software
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.
Apple's Logic Pro X digital audio workstation (DAW) software can create custom MIDI effects plugins using JavaScript.
ECMAScript was included in the 97 standard for scripting nodes of VRML scene description files.
Re-Animator framework allows developing 2D sprite-based games using JavaScript and XML.
game engine supports a modified version of JavaScript for scripting via Mono.
implementation of JavaScript for game and simulation logic.
( software) provides an ECMA standard based scripting engine for tasks automation.
allows users to create custom formulas, automate repetitive tasks and also interact with other Google products such as Gmail.
Many , like
or , use JavaScript for their scripting abilities.
SpinetiX products use the
JavaScript engine to allow scripting within SVG files to create digital signage projects.
uses Javascript as its scripting language.
Microsoft's
technology supports
as a scripting language.
introduced the javax.script package in version 6 that includes a JavaScript implementation based on . Thus, Java applications can host scripts that access the application's variables and objects, much like web browsers host scripts that access a webpage's
C++ toolkit includes a QtScript module to interpret JavaScript, analogous to Java's javax.script package.
JSDB (JavaScript for Databases) is an
JavaScript shell for Windows, Mac OS X, Linux, and Unix, which extends the
with file, database, email, and network objects.
jslibs is an open-source JavaScript shell for Windows and Linux that extends the . It has the ability to call functions in commonly used libraries like NSPR, SQLite, libTomCrypt, OpenGL, OpenAL, and librsvg.
introduced JavaScript for Automation (JXA), which is built upon
and the . It features an
bridge which enables entire
applications to be programmed in JavaScript.
Late Night Software's
(a.k.a. JavaScript for OSA, or JSOSA) is a freeware alternative to
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.
, the programming language used in , is another implementation of the ECMAScript standard.
is a JavaScript runtime that allows developers to create desktop applications.
's AutoShell cross-application scripting environment is built on the
JavaScript engine. It contains -like extensions for command definition, as well as custom classes for various system-related tasks like file I/O, operation system command invocation and redirection, and COM scripting.
, the shell for the
desktop environment, made JavaScript its default programming language in 2013.
platform, which underlies , , and some other web browsers, uses JavaScript to implement the
(GUI) of its various products.
is a JavaScript based framework that allows developers to create applications for smart phones.
's markup language (available since Qt 4.7) uses JavaScript for its application logic. Its declarative syntax is also similar to JavaScript.
is a programming language based on JavaScript that adds support for optional
and some other language extensions such as classes, interfaces and modules. A TS-script compiles into plain JavaScript and can be executed in any JS host supporting
or higher. The compiler is itself written in TypeScript.
provides a JavaScript API for its unified usability interface.
implementation of JavaScript in its
to allow developers to create stand-alone applications solely in JavaScript.
provides a special Windows Library for JavaScript functionality in
that enables the development of
(formerly Metro style) applications in
and JavaScript.
As the specifications of
have increased over the last few years, it has become possible to use JavaScript to control hardware in embedded devices. There are currently two main implementations:
is a JavaScript interpreter for low power microcontrollers
is a microcontroller board with built-in WiFi
Within JavaScript, access to a
becomes invaluable when developing large, non-trivial programs. Because there can be implementation differences between the various browsers (particularly within the ), it is useful to have access to a debugger for each of the browsers that a Web application targets.
Script debuggers are integrated within , , , ,
In addition to the native , three debuggers are available for Internet Explorer:
is the richest of the three, closely followed by
(a component of ), and finally the free
that is far more basic than the other two. The free
provides a limited version of the JavaScript debugging functionality in Microsoft Visual Studio. Internet Explorer has included developer tools since version 8 (reached by pressing the F12 key).
In comparison to Internet Explorer, Firefox has a more comprehensive set of developer tools, which include a debugger as well. Old versions of Firefox without these tools used a
called , or the older
debugger. Also, 's Web Inspector includes a JavaScript debugger, which is used in . A modified version called Blink DevTools is used in .
has node-inspector, an interactive debugger that integrates with the Blink DevTools, available in . Last but not least,
includes a set of tools called .
In addition to the native computer software, there are online JavaScript IDEs, debugging aids are themselves written in JavaScript and built to run on the Web. An example is the program , developed by
who has written extensively on the language. JSLint scans JavaScript code for conformance to a set of standards and guidelines. Many libraries for JavaScript, such as , provide links to demonstration code that can be edited by users. They are also used as a pedagogical tool by institutions such as
to allow students to experience writing code in an environment where they can see the output of their programs, without needing any setup beyond a web browser.
On October 6, 2008 -
developed jsbin, one of the earliest environments to support live updates of JavaScript, CSS, and HTML. He credits 's Learning App,
as inspiration.
The following table is based on information from multiple sources.
Release date
Equivalent to
Old version, no longer supported: 1.0
March 1996
Old version, no longer supported: 1.1
August 1996
Old version, no longer supported: 1.2
Old version, no longer supported: 1.3
October 1998
ECMA-262 1st + 2nd edition
Old version, no longer supported: 1.4
Old version, no longer supported: 1.5
November 2000
ECMA-262 3rd edition
5.5 (JScript 5.5),
6 (JScript 5.6),
7 (JScript 5.7),
8 (JScript 5.8)
1.0-10.0.666
Old version, no longer supported: 1.6
November 2005
1.5 + array extras + array and string generics +
Old version, no longer supported: 1.7
October 2006
+ iterators + let
28.0.1500.95
Old version, no longer supported: 1.8
Old version, no longer supported: 1.8.1
support + minor updates
Old version, no longer supported: 1.8.2
June 22, 2009
1.8.1 + minor updates
, or JavaScript Object Notation, is a general-purpose data interchange format that is defined as a subset of JavaScript's object literal syntax. Like much of JavaScript (regexps and anonymous functions as 1st class elements, closures, flexible classes, 'use strict'), , except for replacing 's key-value operator '=&' by an
inspired ':', is syntactically pure Perl.
is a popular JavaScript library designed to simplify -oriented client-side HTML scripting along with offering cross-browser compatibility because various browsers respond differently to certain vanilla JavaScript code.
is a utility JavaScript library for data manipulation that is used in both client-side and server-side network applications.
Mozilla browsers currently support , 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
to the Java 1.6+ plug-in (not yet supported on the Mac as of March 2010). Most browser inspection tools, such as
in Firefox, include JavaScript interpreters that can act on the visible page's DOM.
is a subset of JavaScript that can be run in any JavaScript engine or run faster in an
(AOT) compiling engine.
As JavaScript is the most widely supported client-side language that can run within a web browser, it has become an
for other languages to target. This has included both newly created languages and ports of existing languages. Some of these include:
, a superset of JavaScript that compiles to standard JavaScript. It adds traditional inheritance and / style dynamic dispatch and optional pseudo-static typing to JavaScript.
, a JavaScript port of Processing, a programming language designed to write visualizations, images, and interactive content. It allows web browsers to display animations, visual applications, games and other graphical rich content without the need for a Java applet or Flash plugin.
, an alternate syntax for JavaScript intended to be more concise and readable. It adds features like array comprehensions (also available in JavaScript since version 1.7) and pattern matching. Like Objective-J, it compiles to JavaScript. Ruby and Python have been cited as influential on CoffeeScript syntax.
translates a subset of Java to JavaScript.
, an object-oriented and functional programming language, has an experimental Scala-to-JavaScript compiler.
, a port of
(translates a subset of Python to JavaScript)
, an open-source programming language developed by Google, can be compiled to JavaScript.
Whalesong, a -to-JavaScript compiler.
, a -backend for porting native libraries to JavaScript.
a programming language that runs on JVM, .NET and JavaScript.
, a free and open-source programming language developed by Microsoft. It is a superset of JavaScript, and essentially adds optional static typing and class-based object-oriented programming to the language.
, an open-source high-level multiplatform programming language and compiler that can produce applications and source code for many different platforms including JavaScript.
ClojureScript, a compiler for
that targets JavaScript. It is designed to emit JavaScript code that is compatible with the advanced compilation mode of the Google Closure optimizing compiler.
language that also compiles to .
A common misconception is that JavaScript is similar or closely related to . It is true that both have a C-like syntax (the C language being their most immediate common ancestor language). They also are both typically
(when used inside a browser), and JavaScript was designed with Java's syntax and standard library in mind. In particular, all Java keywords were reserved in original 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, but the similarities end there.
The differences between the two languages are more prominent than their similarities. Java has , while JavaScript's typing is . Java is loaded from compiled bytecode, while JavaScript is loaded as human-readable source code. Java's objects are , while JavaScript's are . Finally, Java did not support
until Java 8, while JavaScript does, as it contains many features based on .
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