JavaScript

JavaScript, often abbreviated as JS, is a,  that conforms to the  specification. JavaScript has, , , and s.

Alongside and, JavaScript is one of the core technologies of the. JavaScript enables interactive s and is an essential part of s. The vast majority of s use it, and major s have a dedicated to execute it.

As a multi-paradigm language, JavaScript supports, , and (including  and ) s. It has  for working with text, , dates, s, and the , but the language itself does not include any , such as , , or  facilities. It relies upon the host environment in which it is embedded to provide these features.

Initially only implemented in web browsers, JavaScript engines are now embedded in many other types of host software, including  in web servers and databases, and in non-web programs such as word processors and  software, and in runtime environments that make JavaScript available for writing mobile and desktop applications, including desktop widgets.

The terms Vanilla JavaScript and Vanilla JS refer to JavaScript not extended by any frameworks or additional libraries. Scripts written in Vanilla JS are plain JavaScript code.

Although there are similarities between JavaScript and, including language name, , and respective , the two languages are distinct and differ greatly in design. JavaScript was influenced by programming languages such as and. The  format, used to store s in  or transmit them across, is based on JavaScript.

Beginnings at Netscape
In 1993, the (NCSA), a unit of the, released , the first popular graphical , which played an important part in expanding the growth of the nascent  beyond the  niche where the  had formed three years earlier. In 1994, a company called was founded in  and employed many of the original NCSA Mosaic authors to create. However, it intentionally shared no code with NCSA Mosaic. The internal codename for the company's browser was, a portmanteau of "Mosaic and Godzilla". The first version of the Web browser, Mosaic Netscape 0.9, was released in late 1994. Within four months it had already taken three-quarters of the browser market and became the main web browser for the 1990s. To avoid trademark ownership problems with the NCSA, the browser was subsequently renamed Netscape Navigator in the same year, and the company took the name Netscape Communications. Netscape Communications realized that the Web needed to become more dynamic. , the founder of the company, believed that needed a "glue language" that was easy to use by Web designers and part-time programmers to assemble components such as images and plugins, where the code could be written directly in the Web page markup.

In 1995, Netscape Communications recruited with the goal of embedding the  programming language into its Netscape Navigator. Before he could get started, Netscape Communications collaborated with to include Sun's more static programming language,, in Netscape Navigator so as to compete with  for user adoption of Web technologies and platforms. Netscape Communications then decided that the scripting language they wanted to create would complement Java and should have a similar syntax, which excluded adopting other languages such as, , , or Scheme. To defend the idea of JavaScript against competing proposals, the company needed a prototype. Eich wrote one in 10 days, in May 1995.

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 Navigator 2.0 beta 3 in December. The final choice of name caused confusion, giving the impression that the language was a spin-off of the Java programming language, 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 JavaScript was influenced by an earlier Web page scripting language developed by named Cmm (not to be confused with the later  created in 1997). Brendan Eich, however, had never heard of Cmm 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 the Web browser. Nombas later switched to offering JavaScript instead of Cmm in their ScriptEase product and was part of the TC39 group that standardized ECMAScript.

Server-side JavaScript
In December 1995, soon after releasing JavaScript for browsers, Netscape introduced an implementation of the language for with.

Since 1996, the web-server has supported Microsoft's implementation of server-side Javascript——in ASP and .NET pages.

Since the mid-2000s, additional implementations have been introduced, such as  in 2009.

Adoption by Microsoft
Microsoft script technologies including and  were released in 1996. JScript, a implementation of Netscape's JavaScript, was part of. JScript was also available for server-side scripting in. Internet Explorer 3 also included Microsoft's first support for CSS and various extensions to HTML, but in each case the implementation was noticeably different from that found in Netscape Navigator 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 characterized 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 s remained and were obstacles to widespread take-up of JavaScript on the Web.

Standardization
In November 1996, Netscape submitted JavaScript to to carve out a standard specification, which other browser vendors could then implement based on the work done at Netscape. This led to the official release of the language specification published in the first edition of the ECMA-262 standard in June 1997, with JavaScript being the most well known of the implementations. and were other well-known implementations of.

The release of ECMAScript 2 in June 1998 continued the standards process cycle, conforming some modifications to the ISO/IEC 16262 international standard. ECMAScript 3 was released in December 1999 and is the modern-day baseline for JavaScript. The original ECMAScript 4 work led by Waldemar Horwat (then at Netscape, now at ) started in 2000. initially participated and implemented some proposals in their language.

Over time it was clear that Microsoft had no intention of cooperating or implementing proper JavaScript in Internet Explorer, even though they had no competing proposal and they had a partial (and diverged at this point) implementation on the server side. So by 2003, the original ECMAScript 4 work was mothballed.

The next major event was in 2005, with two major happenings in JavaScript's history. First, Brendan Eich and Mozilla rejoined Ecma International as a not-for-profit member and work started on (E4X), the ECMA-357 standard, which came from ex-Microsoft employees at  (originally acquired as Crossgain). This led to working jointly with (later acquired by ), who were implementing E4X in ActionScript 3 (ActionScript 3 was a fork of original ECMAScript 4).

So, along with Macromedia, work restarted on ECMAScript 4 with the goal of standardizing what was in ActionScript 3. To this end, Adobe Systems released the ActionScript Virtual Machine 2, code named, as an project. But Tamarin and ActionScript 3 were too different from web JavaScript to converge, as was realized by the parties in 2007 and 2008.

Alas, there was still turmoil between the various players; —then at —joined forces with Microsoft in 2007 to oppose ECMAScript 4, which led to the ECMAScript 3.1 effort. The development of ECMAScript 4 was never completed, but that work influenced subsequent versions.

While all of this was happening, the open source and developer communities set to work to revolutionize what could be done with JavaScript. This community effort was sparked in 2005 when released a white paper in which he coined the term, and described a set of technologies, of which JavaScript was the backbone, used to create web applications where data can be loaded in the background, avoiding the need for full page reloads and leading to more dynamic applications. This resulted in a renaissance period of JavaScript usage spearheaded by open source libraries and the communities that formed around them, with libraries such as, , , , and others being released.

In July 2008, the disparate parties on either side came together in Oslo. This led to the eventual agreement in early 2009 to rename ECMAScript 3.1 to ECMAScript 5 and drive the language forward using an agenda that is known as Harmony. ECMAScript 5 was finally released in December 2009.

In June 2011, ECMAScript 5.1 was released to fully align with the third edition of the ISO/IEC 16262 international standard. ECMAScript 2015 was released in June 2015. ECMAScript 2016 was released in June 2016. The current version is ECMAScript 2017, released in June 2017.

Later developments
JavaScript has become one of the most popular programming languages on the Web. However, many professional programmers initially denigrated the language due to the perceived target audience of Web authors and other such "amateurs". 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 s and JavaScript-heavy sites, it is increasingly being used as a compile target for s from both and.

Trademark
"JavaScript" is a of  in the United States. It is used under license for technology invented and implemented by Netscape Communications and current entities such as the.

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

Universal support
All popular modern Web browsers support JavaScript with built-in interpreters.

Imperative and structured
JavaScript supports much of the syntax from  (e.g.,   statements,   loops,   statements,   loops, etc.). One partial exception is : JavaScript originally had only with. ECMAScript 2015 added keywords  and   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:JavaScript is like most other s. A  is associated with a  rather than an expression. For example, a  initially bound to a number may be reassigned to a .  JavaScript supports various ways to test the type of objects, including.
 * Run-time evaluation: JavaScript includes an  function that can execute statements provided as strings at run-time.

Prototype-based (object-oriented)
JavaScript is almost entirely. In JavaScript, an is an, augmented with a prototype (see below); each string key provides the name for an object property, and there are two syntactical ways to specify such a name: dot notation  and bracket notation. A property may be added, rebound, or deleted at run-time. Most properties of an object (and any property that belongs to an object's prototype inheritance chain) can be enumerated using a  loop.

JavaScript has a small number of built-in objects, including  and.


 * 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  prototype). ECMAScript 5 offers the   method, allowing explicit creation of an instance without automatically inheriting from the   prototype (older environments can assign the prototype to  ). The constructor's   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   or , also have prototypes that can be modified. While it is possible to modify the   prototype, it is generally considered bad practice because most objects in JavaScript will inherit methods and properties from the   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 during function calling; 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.

Functional
A is ; a function is considered to be an object. As such, a function may have properties and methods, such as  and. A nested function is a function defined within another function. It is created each time the outer function is invoked. In addition, each nested function forms a : The of the outer function (including any constant, local variable, or argument value) becomes part of the internal state of each inner function object, even after execution of the outer function concludes. JavaScript also supports s.

Delegative
JavaScript supports implicit and explicit.


 * Functions as roles (Traits and Mixins): JavaScript natively supports various function-based implementations of patterns like  and s. Such a function defines additional behavior by at least one method bound to the   keyword within its   body. A Role then has to be delegated explicitly via   or   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.

Miscellaneous

 * 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 ). It also relies on the run-time environment to provide the ability to include/import scripts (e.g.,   elements). This is not a language feature per se, but it is common in most JavaScript implementations. JavaScript processes  from a  one at a time. JavaScript calls a  associated with each new message, creating a  frame with the function's  and s. The call stack shrinks and grows based on the function's needs. When the call stack is empty upon function completion, 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 s and also through the local  object.  can also be created by using the   method.


 * 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 s 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.

Vendor-specific extensions
JavaScript is officially managed by, and new language features are added periodically. However, only some s support these new features:
 * property getter and setter functions (supported by WebKit, Gecko, Opera, ActionScript, and Rhino)
 * conditional  clauses
 * iterator protocol (adopted from )
 * shallow -s (adopted from Python)
 * and generator expressions (adopted from Python)
 * proper block scope via the  keyword
 * array and object destructuring (limited form of )
 * concise function expressions
 * (E4X), an extension that adds native XML support to ECMAScript (unsupported in Firefox since version 21)

Simple examples
in JavaScript can be defined using either the,   or   keywords.

Note the in the example above, all of which were preceded with two.

There is no built-in functionality in JavaScript; 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  object that can be used to print output. Here is a minimalist in JavaScript:

A simple function:

An (or lambda):

This example shows that, in JavaScript, capture their non-local variables by reference.

Arrow functions were first introduced in. They shorten the syntax for writing functions in JavaScript. Arrow functions are anonymous in nature; a variable is needed to refer to them in order to invoke them after their creation.

Example of arrow function:

In JavaScript, are created in the same way as functions; this is known as a.

Object example:

demonstration ( is a special ):

s are often used to create modules; before ECMAScript 2015 there was no built-in module construct in the language. Modules allow gathering properties and methods in a namespace and making some of them private:

Exporting and Importing modules in javascript

Export example:

Import example:

More advanced example
This sample code displays various JavaScript features.

The following output should be displayed in the browser window.

Use in Web pages
94.5% of 10 million most popular web pages used JavaScript. The most common use of JavaScript is to add client-side behavior to pages, also known as  (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.

JavaScript code can run locally in a user's browser (rather than on a remote server), increasing the application's overall responsiveness to user actions. JavaScript code can also 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 Ajax programming similarly exploits this strength.

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

A Web browser is the most common host environment for JavaScript. However, a Web browsers does not have to execute JavaScript code. (For example, have no JavaScript engines; and users of other browsers may disable scripts through a preference or .)

A Web browser typically creates "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.

JavaScript is the only language that the most popular browsers share support for and has inadvertently become a for frameworks in other languages. The increasing speed of JavaScript engines has made the language a feasible compilation target, despite the performance limitations inherent to its dynamic nature.

Example script
Below is a minimal example of a standards-conforming Web page containing JavaScript (using syntax) and the DOM:

Compatibility considerations
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 are officially defined by the in a standardization effort separate from JavaScript. The implementation of these DOM interfaces differ between web browsers.

JavaScript authors can deal with these differences by writing standards-compliant code that can be executed correctly by most browsers. Failing that, they can write code that behaves differently in the absence of certain browser features. Authors may also find it practical to detect what browser is running, as two browsers may implement the same feature with differing behavior. Libraries and toolkits that take browser differences into account are also useful to programmers.

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 or  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. Some sites use the HTML  tag, which contains alt content if JS is disabled. 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.

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 minimize 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 ECMAScript (SES)—that provide greater levels of security, especially on code created by third parties (such as advertisements). is another project for safe embedding and isolation of third-party JavaScript and HTML.

is the main intended method of ensuring that only trusted code is executed on a Web page.

Cross-site vulnerabilities
A common JavaScript-related security problem is (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 (CSRF). In CSRF, code on an attacker's site tricks the victim's browser into taking actions the user did not intend at a target site (like transferring money at a bank). When target sites rely solely on cookies for request authentication, requests originating from code on the attacker's site can carry the same valid login credentials of the initiating 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  tag on an attacker's site exploits a page on the victim's site that returns private information such as  or JavaScript. Possible solutions include:


 * requiring an authentication token in the and  parameters for any response that returns private information.

Misplaced trust in the client
Developers of client-server applications must recognize that untrusted clients may be under the control of attackers. The application author cannot assume that their 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 cannot be relied on to prevent operations such as right-clicking on an image to save it.
 * It is considered very bad practice to embed sensitive information such as passwords in JavaScript because it can be extracted by an attacker.

Misplaced trust in developers
Package management systems such as and  are popular with JavaScript developers. Such systems allow a developer to easily manage their program's dependencies upon other developer's program libraries. Developers trust that the maintainers of the libraries will keep them secure and up to date, but that is not always the case. A vulnerability has emerged because of this blind trust. Relied-upon libraries can have new releases that cause bugs or vulnerabilities to appear in all programs that rely upon the libraries. Inversely, a library can go unpatched with known vulnerabilities out in the wild. In a study done looking over a sample of 133k websites, researchers found 37% of the websites included a library with at-least one known vulnerability. "The median lag between the oldest library version used on each website and the newest available version of that library is 1,177 days in ALEXA, and development of some libraries still in active use ceased years ago." Another possibility is that the maintainer of a library may remove the library entirely. This occurred in March 2016 when Azer Koçulu removed his repository from. This caused all tens of thousands of programs and websites depending upon his libraries to break.

Browser and plugin coding errors
JavaScript provides an interface to a wide range of browser capabilities, some of which may have flaws such as s. 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 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".

Sandbox implementation errors
Web browsers are capable of running JavaScript outside the sandbox, with the privileges necessary to, for example, create or delete files. Such privileges are not intended 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.

Hardware vulnerabilities
In 2015, a JavaScript-based proof-of-concept implementation of a attack was described in a paper by security researchers.

In 2017, a JavaScript-based attack via browser was demonstrated that could bypass. It's called "ASLR⊕Cache" or AnC.

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 that provides access to the host environment. The core JavaScript language remains mostly the same in each application.

Embedded scripting language

 * Google's extensions, 's extensions, Apple's  extensions, Apple's, Microsoft's , , , and   are implemented using JavaScript.
 * The database accepts queries written in JavaScript.  and  are the core components of : a  for creating Web applications using just JavaScript.
 * The database accept queries written in JS/SQL, which is a combination of  and JavaScript.  has built-in computing engine that allows execution of JavaScript code right inside the.
 * Adobe's support JavaScript in  files.
 * Tools in the, including , , , , and , allow scripting through JavaScript.
 * , an office application suite, allows JavaScript to be used as a scripting language.
 * The visual programming language, released by Cycling '74, offers a JavaScript model of its environment for use by developers. It allows users to reduce visual clutter by using an object for a task rather than many.
 * Apple's Logic Pro X digital audio workstation (DAW) software can create custom MIDI effects plugins using JavaScript.
 * The game engine supported a modified version of JavaScript for scripting via Mono until 2017.
 * (3D engine) uses the implementation of JavaScript for game and simulation logic.
 * ( software) provides an ECMA standard based scripting engine for tasks automation.
 * in and  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.
 * MV uses JavaScript as its scripting language.
 * The text editor uses JavaScript 1.7 as internal scripting language, introduced with version 13 in 2007.

Scripting engine

 * Microsoft's technology supports  as a scripting language.
 * introduced the  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  (DOM).
 * The C++ toolkit includes a   module to interpret JavaScript, analogous to Java's   package.
 * introduced (JXA), which is built upon  and the . It features an  bridge that enables entire  applications to be programmed in JavaScript.
 * Late Night Software's (also known as JavaScript for OSA, or JSOSA) is a freeware alternative to  for OS X. It is based on the Mozilla JavaScript 1.5 implementation, with the addition of a   object for interaction with the operating system and third-party applications.

Application platform

 * , the programming language used in, is another implementation of the ECMAScript standard.
 * (Adobe Integrated Runtime) is a JavaScript runtime that allows developers to create desktop applications.
 * is an open-source developed by.
 * 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.
 * is a mobile application development framework
 * is an open source software framework. It can be used to build games, apps and other cross platform GUI based interactive programs
 * (CEF) is an open source framework for embedding a based on the  core
 * is a set of development tools for creating data-centric, cross-platform, native mobile consumer and enterprise applications.
 * call all Node.js modules directly from DOM and enable a new way of writing applications with all Web technologies.
 * , the shell for the 3 desktop environment, made JavaScript its default programming language in 2013.
 * The (XPFE) platform, which underlies, , and some other Web browsers, uses JavaScript to implement the  (GUI) of its various products.
 * 's markup language (available since Qt 4.7) uses JavaScript for its application logic. Its declarative syntax is also similar to JavaScript.
 * provides a JavaScript API for its unified usability interface.
 * is the next generation of web-centric platforms built to run on a wide range of form factors.
 * is a framework to develop apps for all major platforms, from phones and tablets to PCs and TVs
 * provides a special Windows Library for JavaScript functionality in that enables the development of  (formerly Metro style) applications in  and JavaScript.
 * is an open-source framework to develop apps on the Apple iOS and Android platforms.
 * is a framework for building Mobile cross-platform UI, created by China Tech giant
 * is packaged version of the Mozilla platform to enable standalone desktop application development

Development tools
Within JavaScript, access to a becomes invaluable when developing large, non-trivial programs. There can be implementation differences between the various browsers (particularly within the DOM), so it is useful to have access to a debugger for each of the browsers that a Web application targets.

Script debuggers are integrated within many mainstream browsers such as, , , , and.

In addition to the native, three other debuggers are available for Internet Explorer: has the most features of the three, closely followed by  (a component of ), and finally the free. The free provides a limited version of the JavaScript debugging functionality in Microsoft Visual Studio.

In comparison to Internet Explorer, Firefox has a more comprehensive set of developer tools, which includes a debugger as well. Old versions of Firefox without these tools used a called, or the older  debugger. '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. includes a set of tools called.

In addition to the native computer software, there are online JavaScript integrated development environment (IDEs), which has debugging aids that 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. Demonstration codes 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.

Benchmark tools for developers
JavaScript's increased usage in web development warrants further considerations about performance. code has inherited many responsibilities previously handled by the. Mobile devices in particular may encounter problems rendering poorly optimized frontend code.

A library for doing benchmarks is benchmark.js. A benchmarking library that supports high-resolution timers and returns statistically significant results.

Another tool is jsben.ch. An online JavaScript benchmarking tool, where code snippets can be tested against each other.

Version history
JavaScript was initially developed in 1996 for use in the Web browser. In the same year Microsoft released an implementation for Internet Explorer. This implementation was called due to trademark issues. In 1997, the first standardized version of the language was released under the name in the first edition of the ECMA-262 standard.

The explicit versioning and opt-in of language features was Mozilla-specific and has been removed in later Firefox versions (at least by Firefox 59). Firefox 4 was the last version which referred to an explicit JavaScript version (1.8.5). With new editions of the ECMA-262 standard, JavaScript language features are now often mentioned with their initial definition in the ECMA-262 editions.

The following table of explicitly versioned JavaScript versions is based on information from multiple sources.

Related languages and technologies

 * , or JavaScript Object Notation, is a general-purpose data interchange format that is defined as a subset of JavaScript's object literal syntax.


 * is a 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.


 * and are s to use for developing s and also cross-platform mobile apps.


 * is an JavaScript library providing views that are rendered using components specified as custom HTML tags.


 * is an JavaScript framework that features an incrementally adoptable architecture focusing on declarative rendering and component composition.


 * Mozilla browsers currently support, a feature that allows JavaScript and Java to intercommunicate on the Web. However, Mozilla-specific support for LiveConnect was 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 ). 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.


 * is an . Programs are written using only six different characters, but are still valid JavaScript code.


 * is an object oriented JavaScript library designed for artists and designers. It is based on the ideas of the project but is for the web.


 * jsben.ch is an online JavaScript benchmarking tool, where different code snippets can be tested against each other.

Use as an intermediate language
As JavaScript is the most widely supported client-side language that can run within a Web browser, it has become an for other languages (also called transpilers) to target. This has included both newly created languages and ports of existing languages. Some of these include: As JavaScript has unusual limitations – such as no explicit integer type, only double-precision binary floating point – languages that compile to JavaScript and do not take care to use the integer-converting shift and bitwise logical operators may have slightly different behavior than in other environments.
 * ClojureScript, a dialect of that targets JavaScript. Its compiler is designed to emit JavaScript code that is compatible with the advanced compilation mode of the.
 * , 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.
 * , an all-purpose, language that compiles to JavaScript.
 * , a pure functional language for web apps. Unlike handwritten JavaScript, Elm-generated JavaScript has zero runtime exceptions, a time-traveling debugger, and enforced semantic versioning.
 * , a -backend for porting native libraries to JavaScript, known as
 * , a programming language that runs on JVM, .NET and JavaScript.
 * , a compiler for that targets JavaScript.
 * , a toolkit that translates a subset of Java to JavaScript.
 * , an open-source high-level multiplatform programming language and compiler that can produce applications and source code for many different platforms including JavaScript.
 * OberonScript, a full implementation of the programming language that compiles to high-level JavaScript.
 * , 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 the Processing 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.
 * , a port of to  that translates a subset of Python to JavaScript.
 * , an object-oriented and functional programming language, has a Scala-to-JavaScript compiler.
 * , a virtual machine and DOM environment for the open-source implementation of the  programming language.
 * , a free and open-source programming language developed by Microsoft. It is a superset of JavaScript, and essentially adds support for optional s 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 3 or higher. The compiler is itself written in TypeScript.
 * Whalesong, a -to-JavaScript compiler.

JavaScript and Java
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 and  objects are based on classes from Java 1.0, but the similarities end there.

and JavaScript both first appeared in 1995, but Java was developed by of Sun Microsystems, and JavaScript by  of Netscape Communications.

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 functional programming until Java 8, while JavaScript has done so from the beginning, being influenced by.

WebAssembly
Starting in 2017, web browsers began supporting, a technology standardized by the. The WebAssembly standard specifies a binary format, which can be produced by a compiler toolchain such as, to execute in the browser at near native speed. WebAssembly allows programming languages such as C, C++, C# and Java to be used as well as JavaScript to author client-side code for the World Wide Web.