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v t e

JavaScript
JavaScript
(/ˈdʒɑːvəˌskrɪpt/),[6] often abbreviated as JS, is a high-level, interpreted programming language. It is a language which is also characterized as dynamic, weakly typed, prototype-based and multi-paradigm. Alongside HTML
HTML
and CSS, JavaScript
JavaScript
is one of the three core technologies of World Wide Web
World Wide Web
content engineering. It is used to make dynamic webpages interactive and provide online programs, including video games. The majority of websites employ it, and all modern web browsers support it without the need for plug-ins by means of a built-in JavaScript
JavaScript
engine. Each of the many JavaScript
JavaScript
engines represent a different implementation of JavaScript, all based on the ECMAScript specification, with some engines not supporting the spec fully, and with many engines supporting additional features beyond ECMA. As a multi-paradigm language, JavaScript
JavaScript
supports event-driven, functional, and imperative (including object-oriented and prototype-based) programming styles. It has an API for working with text, arrays, dates, regular expressions, and basic manipulation of the DOM, but the language itself does not include any I/O, such as networking, storage, or graphics facilities, relying for these upon the host environment in which it is embedded. Initially only implemented client-side in web browsers, JavaScript engines are now embedded in many other types of host software, including server-side in web servers and databases, and in non-web programs such as word processors and PDF software, and in runtime environments that make JavaScript
JavaScript
available for writing mobile and desktop applications, including desktop widgets. Although there are strong outward similarities between JavaScript
JavaScript
and Java, including language name, syntax, and respective standard libraries, the two languages are distinct and differ greatly in design; JavaScript
JavaScript
was influenced by programming languages such as Self and Scheme.[7]

Contents

1 History

1.1 Beginnings at Netscape 1.2 Server-side JavaScript 1.3 Adoption by Microsoft 1.4 Standardization 1.5 Later developments

2 Trademark 3 Vanilla JavaScript 4 Features

4.1 Universal support 4.2 Imperative and structured 4.3 Dynamic 4.4 Prototype-based (object-oriented) 4.5 Functional 4.6 Delegative 4.7 Miscellaneous 4.8 Vendor-specific extensions

5 Syntax

5.1 Simple examples 5.2 More advanced example

6 Use in Web pages

6.1 Example script 6.2 Compatibility considerations

7 Security

7.1 Cross-site vulnerabilities 7.2 Misplaced trust in the client 7.3 Misplaced trust in developers 7.4 Browser and plugin coding errors 7.5 Sandbox implementation errors 7.6 Hardware vulnerabilities

8 Uses outside Web pages

8.1 Embedded scripting language 8.2 Scripting engine 8.3 Application platform

9 Development tools 10 Benchmark tools for developers 11 Version history 12 Related languages and technologies

12.1 Use as an intermediate language 12.2 JavaScript
JavaScript
and Java 12.3 WebAssembly

13 See also 14 References 15 Further reading 16 External links

History[edit] Beginnings at Netscape[edit] In 1993, the National Center for Supercomputing Applications
National Center for Supercomputing Applications
(NCSA), a unit of the University of Illinois at Urbana-Champaign, released NCSA Mosaic, the first popular graphical Web browser, which played an important part in expanding the growth of the nascent World Wide Web. In 1994, a company called Mosaic Communications was founded in Mountain View, California
Mountain View, California
and employed many of the original NCSA Mosaic authors to create Mosaic Netscape. However, it intentionally shared no code with NCSA Mosaic. The internal codename for the company's browser was Mozilla, which stood for "Mosaic killer", as the company's goal was to displace NCSA Mosaic as the world's number one web browser. 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 browser for the Internet in the 1990s. To avoid trademark ownership problems with the NCSA, the browser was subsequently renamed Netscape
Netscape
Navigator in the same year, and the company took the name Netscape Communications. Netscape
Netscape
Communications realized that the Web needed to become more dynamic. Marc Andreessen, the founder of the company believed that HTML
HTML
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
Netscape
Communications recruited Brendan Eich
Brendan Eich
with the goal of embedding the Scheme programming language into its Netscape Navigator.[8] Before he could get started, Netscape
Netscape
Communications collaborated with Sun Microsystems
Sun Microsystems
to include in Netscape
Netscape
Navigator Sun's more static programming language Java, in order to compete with Microsoft
Microsoft
for user adoption of Web technologies and platforms.[9] Netscape
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 Perl, Python, TCL, or Scheme. To defend the idea of JavaScript
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
Netscape
Navigator 2.0 in September 1995, but it was renamed JavaScript[2] when it was deployed in the Netscape
Netscape
Navigator 2.0 beta 3 in December.[10] 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[11] as a marketing ploy by Netscape
Netscape
to give JavaScript
JavaScript
the cachet of what was then the hot new Web programming language. There is a common misconception that JavaScript
JavaScript
was influenced by an earlier Web page scripting language developed by Nombas named Cmm (not to be confused with the later C-- created in 1997).[12][13] Brendan Eich, however, had never heard of Cmm before he created LiveScript.[14] Nombas did pitch their embedded Web page scripting to Netscape, though Web page scripting was not a new concept, as shown by the ViolaWWW
ViolaWWW
Web browser.[15] Nombas later switched to offering JavaScript
JavaScript
instead of Cmm in their ScriptEase product and was part of the TC39 group that standardized ECMAScript.[16] Server-side JavaScript[edit] In December 1995, soon after releasing JavaScript
JavaScript
for browsers, Netscape
Netscape
introduced an implementation of the language for server-side scripting with Netscape
Netscape
Enterprise Server.[17] Since 1996, the IIS web-server has supported Microsoft's implementation of Javascript -- JScript -- in ASP and .NET pages. Since the mid-2000s, additional server-side JavaScript
JavaScript
implementations have been introduced, such as Node.js
Node.js
in 2009.[18] Adoption by Microsoft[edit] Microsoft
Microsoft
script technologies including VBScript and JScript were released in 1996. JScript, a reverse-engineered implementation of Netscape's JavaScript, was part of Internet Explorer
Internet Explorer
3. JScript was also available for server-side scripting in Internet Information Server. Internet Explorer 3
Internet Explorer 3
also included Microsoft's first support for CSS
CSS
and various extensions to HTML, but in each case the implementation was noticeably different to that found in Netscape Navigator at the time.[19][20] 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 browser wars.[21] JavaScript
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.[19] With the release of Internet Explorer
Internet Explorer
4, Microsoft
Microsoft
introduced the concept of Dynamic HTML, but the differences in language implementations and the different and proprietary Document Object Models remained and were obstacles to widespread take-up of JavaScript
JavaScript
on the Web.[19] Standardization[edit] In November 1996, Netscape
Netscape
submitted JavaScript
JavaScript
to Ecma International 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 ECMAScript published in the first edition of the ECMA-262 standard in June 1997, with JavaScript
JavaScript
being the most well known of the implementations. ActionScript
ActionScript
and JScript are other well-known implementations of ECMAScript. The standards process continued in cycles, with the release of ECMAScript 2 in June 1998, which brings some modifications to conform to the ISO/IEC 16262 international standard. The release of ECMAScript 3 followed in December 1999, which is the baseline for modern day JavaScript. The original ECMAScript 4 work led by Waldemar Horwat (then at Netscape, now at Google) started in 2000 and at first, Microsoft
Microsoft
seemed to participate and even implemented some of the proposals in their JScript .NET language. Over time it was clear though that Microsoft
Microsoft
had no intention of cooperating or implementing proper JavaScript
JavaScript
in Internet Explorer, even though they had no competing proposal and they had a partial (and diverged at this point) implementation on the .NET 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
Brendan Eich
and Mozilla
Mozilla
rejoined Ecma International as a not-for-profit member and work started on ECMAScript for XML
XML
(E4X), the ECMA-357 standard, which came from ex- Microsoft
Microsoft
employees at BEA Systems (originally acquired as Crossgain). This led to working jointly with Macromedia
Macromedia
(later acquired by Adobe Systems), who were implementing E4X in ActionScript 3 ( ActionScript
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
ActionScript
3. To this end, Adobe Systems released the ActionScript
ActionScript
Virtual Machine 2, code named Tamarin, as an open source project. But Tamarin and ActionScript
ActionScript
3 were too different from web JavaScript
JavaScript
to converge, as was realized by the parties in 2007 and 2008. Alas, there was still turmoil between the various players; Douglas Crockford—then at Yahoo!—joined forces with Microsoft
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.[22] 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 Jesse James Garrett released a white paper in which he coined the term Ajax, and described a set of technologies, of which JavaScript
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
JavaScript
usage spearheaded by open source libraries and the communities that formed around them, with libraries such as Prototype, jQuery, Dojo Toolkit, MooTools, 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.[3] Later developments[edit] JavaScript
JavaScript
has become one of the most popular programming languages on the Web. Initially, however, many professional programmers denigrated the language because, among other reasons, its target audience consisted of Web authors and other such "amateurs".[23] The advent of Ajax returned JavaScript
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
JavaScript
outside Web browsers, as seen by the proliferation of Server-side JavaScript platforms. In January 2009, the CommonJS
CommonJS
project was founded with the goal of specifying a common standard library mainly for JavaScript
JavaScript
development outside the browser.[24] With the rise of single-page applications and JavaScript-heavy sites, it is increasingly being used as a compile target for source-to-source compilers from both dynamic languages and static languages. Trademark[edit] "JavaScript" is a trademark of Oracle Corporation
Oracle Corporation
in the United States.[25] It is used under license for technology invented and implemented by Netscape
Netscape
Communications and current entities such as the Mozilla
Mozilla
Foundation.[26] Vanilla JavaScript[edit] The terms Vanilla JavaScript
JavaScript
and Vanilla JS refer to JavaScript
JavaScript
not extended by any frameworks or additional libraries. Scripts written in Vanilla JS are plain JavaScript
JavaScript
code.[27][28] Features[edit] The following features are common to all conforming ECMAScript implementations, unless explicitly specified otherwise. Universal support[edit] All modern Web browsers support JavaScript
JavaScript
with built-in interpreters. Imperative and structured[edit] JavaScript
JavaScript
supports much of the structured programming syntax from C (e.g., if statements, while loops, switch statements, do while loops, etc.). One partial exception is scoping: JavaScript
JavaScript
originally had only function scoping with var. ECMAScript 2015 added keywords let and const for block scoping, meaning JavaScript
JavaScript
now has both function and block scoping. Like C, JavaScript
JavaScript
makes a distinction between expressions and statements. One syntactic difference from C is automatic semicolon insertion, which allows the semicolons that would normally terminate statements to be omitted.[29] Dynamic[edit]

Typing As with most scripting languages, JavaScript
JavaScript
is dynamically typed; a type is associated with each value, rather than just with each expression. For example, a variable that is at one time bound to a number may later be re-bound to a string.[30] JavaScript
JavaScript
supports various ways to test the type of an object, including duck typing.[31] Run-time evaluation JavaScript
JavaScript
includes an eval function that can execute statements provided as strings at run-time.

Prototype-based (object-oriented)[edit] JavaScript
JavaScript
is almost entirely object-based. In JavaScript, an object is an associative array, 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 (obj.x = 10) and bracket notation (obj['x'] = 10). 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 for...in loop. JavaScript
JavaScript
has a small number of built-in objects, including Function and Date.

Prototypes JavaScript
JavaScript
uses prototypes where many other object-oriented languages use classes for inheritance.[32] It is possible to simulate many class-based features with prototypes in JavaScript.[33] 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).[34] 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).[35] 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
JavaScript
will inherit methods and properties from the Object prototype, and they may not expect the prototype to be modified.[36] 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; 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[edit] A function is first-class; a function is considered to be an object. As such, a function may have properties and methods, such as .call() and .bind().[37] 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 lexical closure: The lexical scope 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.[38] JavaScript
JavaScript
also supports anonymous functions. Delegative[edit] JavaScript
JavaScript
supports implicit and explicit delegation.

Functions as roles (Traits and Mixins) JavaScript
JavaScript
natively supports various function-based implementations of Role[39] patterns like Traits[40][41] and Mixins.[42] 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
Object composition
and inheritance Whereas explicit function-based delegation does cover composition 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 inheritance in JavaScript
JavaScript
is covered by a delegation automatism that is bound to the prototype property of constructor functions.

Miscellaneous[edit]

Run-time environment JavaScript
JavaScript
typically relies on a run-time environment (e.g., a Web browser) 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., HTML
HTML
<script> elements). This is not a language feature per se, but it is common in most JavaScript
JavaScript
implementations.

JavaScript
JavaScript
processes messages from a queue one at a time. Upon loading a new message, JavaScript
JavaScript
calls a function associated with that message, which creates a call stack frame (the function's arguments and local variables). The call stack shrinks and grows based on the function's needs. Upon function completion, when the stack is empty, JavaScript
JavaScript
proceeds to the next message in the queue. This is called the event loop, described as "run to completion" because each message is fully processed before the next message is considered. However, the language's concurrency model describes the event loop as non-blocking: program input/output is performed using events and callback functions. This means, for instance, that JavaScript
JavaScript
can process a mouse click while waiting for a database query to return information.[43]

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. Variadic functions can also be created by using the bind method.

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
JSON
data format.

Regular expressions JavaScript
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.[44]

Vendor-specific extensions[edit] JavaScript
JavaScript
is officially managed by Mozilla
Mozilla
Foundation, and new language features are added periodically. However, only some JavaScript
JavaScript
engines support these new features:

property getter and setter functions (supported by WebKit, Gecko, Opera,[45] ActionScript, and Rhino)[46] conditional catch clauses iterator protocol (adopted from Python) shallow generators-coroutines (adopted from Python) array comprehensions and generator expressions (adopted from Python) proper block scope via the let keyword array and object destructuring (limited form of pattern matching) concise function expressions (function(args) expr) ECMAScript for XML
XML
(E4X), an extension that adds native XML
XML
support to ECMAScript (unsupported in Firefox
Firefox
since version 21[47])

Syntax[edit] Main article: JavaScript
JavaScript
syntax Simple examples[edit] Variables in JavaScript
JavaScript
can be defined using the var keyword:[48]

var x; // defines the variable x and assigns to it the special value "undefined" (not to be confused with an undefined value) var y = 2; // defines the variable y and assigns to it the value 2 var z = "Hello, World!"; // defines the variable z and assigns to it a string containing "Hello, World!"

Note the comments in the example above, all of which were preceded with two forward slashes. There is no built-in I/O functionality in JavaScript; the run-time environment provides that. The ECMAScript specification in edition 5.1 mentions:[49]

… 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[50] that can be used to print output. Here is a minimalist Hello World program
Hello World program
in JavaScript:

console.log("Hello World!");

A simple recursive function:

function factorial(n) if (n === 0) return 1; // 0! = 1

return n * factorial(n - 1);

factorial(3); // returns 6

An anonymous function (or lambda):

function counter() var count = 0; return function() return ++count; ;

var closure = counter(); closure(); // returns 1 closure(); // returns 2 closure(); // returns 3

This example shows that, in JavaScript, function closures capture their non-local variables by reference. In JavaScript, objects are created in the same way as functions, this is known as a function object. Object example:

function Ball(r) this.radius = r; //the radius variable is local to the ball object this.area = pi*r**2; this.show = function() //objects can contain functions drawCircle(r); //references a circle drawing function

myBall = new Ball(5); //creates a new instance of the ball object with radius 5 myBall.show(); //this instance of the ball object has the show function performed on it

Variadic function demonstration (arguments is a special variable):[51]

function sum() var x = 0; for (var i = 0; i < arguments.length; ++i) x += arguments[i];

return x;

sum(1, 2); // returns 3 sum(1, 2, 3); // returns 6

Immediately-invoked function expressions are often used to create modules, as before ECMAScript 2015 there was no built-in construct in the language. Modules allow gathering properties and methods in a namespace and making some of them private:

var counter = (function () var i = 0; // private property

return // public methods get: function () alert(i); , set: function (value) i = value; , increment: function () alert(++i);

; )(); // module

counter.get(); // shows 0 counter.set(6); counter.increment(); // shows 7 counter.increment(); // shows 8

More advanced example[edit] This sample code displays various JavaScript
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"); // var a = mouseX ;

return x

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 t = b; b = a; a = t;

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. // 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() return a; ; return a; , // 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 generic output function; 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
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((a, b) => a.lcm() - b.lcm()) // sort with this comparative function; => is a shorthand form of a function, called "arrow function" .forEach(printResult);

function printResult(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

Use in Web pages[edit] See also: Dynamic HTML
HTML
and Ajax (programming) As of May 2017 94.5% of 10 million most popular web pages used JavaScript.[52] The most common use of JavaScript
JavaScript
is to add client-side behavior to HTML
HTML
pages, also known as Dynamic HTML (DHTML). Scripts are embedded in or included from HTML
HTML
pages and interact with the Document Object Model
Document Object Model
(DOM) of the page. Some simple examples of this usage are:

Loading new page content or submitting data to the server via Ajax 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. Validating input values of a Web form 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 Web analytics, ad tracking, personalization or other purposes.

Because JavaScript
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
JavaScript
code can detect user actions that HTML
HTML
alone cannot, such as individual keystrokes. Applications such as Gmail
Gmail
take advantage of this: much of the user-interface logic is written in JavaScript, and JavaScript
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
JavaScript
interpreter or JavaScript
JavaScript
implementation) is an interpreter that interprets JavaScript
JavaScript
source code and executes the script accordingly. The first JavaScript engine was created by Brendan Eich
Brendan Eich
at Netscape, for the Netscape
Netscape
Navigator Web browser. The engine, code-named SpiderMonkey, is implemented in C. It has since been updated (in JavaScript
JavaScript
1.5) to conform to ECMAScript 3. The Rhino engine, created primarily by Norris Boyd (formerly at Netscape, now at Google) is a JavaScript implementation in Java. Rhino, like SpiderMonkey, is ECMAScript 3 compliant. A Web browser
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 Web server
Web server
is another common host environment. A JavaScript
JavaScript
Web server
Web server
would typically expose host objects representing HTTP
HTTP
request and response objects, which a JavaScript
JavaScript
program could then interrogate and manipulate to dynamically generate Web pages. Because JavaScript
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
JavaScript
was never intended to be such a language.[53] Despite the performance limitations inherent to its dynamic nature, the increasing speed of JavaScript
JavaScript
engines has made the language a surprisingly feasible compilation target. Example script[edit] Below is a minimal example of a standards-conforming Web page containing JavaScript
JavaScript
(using HTML
HTML
5 syntax) and the DOM:

<!DOCTYPE html> <html> <head> <title>Example</title> </head> <body> <button id="hellobutton">Hello</button> <script> document.getElementById('hellobutton').onclick = function() alert('Hello world!'); // Show a dialog var myTextNode = document.createTextNode('Some new words.'); document.body.appendChild(myTextNode); // Append "Some new words" to the page ; </script> </body> </html>

Compatibility considerations[edit] Main article: Web interoperability Because JavaScript
JavaScript
runs in widely varying environments, an important part of testing and debugging is to test and verify that the JavaScript
JavaScript
works across multiple browsers. The DOM interfaces for manipulating Web pages are not part of the ECMAScript standard, or of JavaScript
JavaScript
itself. Officially, the DOM interfaces 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
JavaScript
authors can attempt to write standards-compliant code that 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.[54] 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.[55][56] 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; use a PDA or mobile phone browser that cannot execute JavaScript; have JavaScript
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 degrade gracefully 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
JavaScript
would have added. Some sites use the HTML
HTML
<noscript> 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 progressive enhancement. Security[edit] See also: Browser security JavaScript
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 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. 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).[57][58] Caja is another project for safe embedding and isolation of third-party JavaScript
JavaScript
and HTML. Content Security Policy
Content Security Policy
is the main intended method of ensuring that only trusted code is executed on a Web page. See also: Content Security Policy Cross-site vulnerabilities[edit] Main articles: Cross-site scripting and Cross-site request forgery A common JavaScript-related security problem is cross-site scripting (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
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.[59] Another cross-site vulnerability is cross-site request forgery (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
HTTP
Referrer header can also help. " JavaScript
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
JSON
or JavaScript. Possible solutions include:

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

Misplaced trust in the client[edit] 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
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 obfuscated, but obfuscation can be reverse-engineered. JavaScript
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
JavaScript
can't be relied on to prevent operations such as right-clicking on an image to save it.[60] It is extremely bad practice to embed sensitive information such as passwords in JavaScript
JavaScript
because it can be extracted by an attacker.

Misplaced trust in developers[edit] Package management systems such as npm and Bower are popular with JavaScript
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.[61] "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."[61] 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 npm. This caused all tens of thousands of programs and websites depending upon his libraries to break.[62][63] Browser and plugin coding errors[edit] JavaScript
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 that would run any code they wish on the user's system. This code is not by any means limited to another JavaScript
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,[64] Internet Explorer,[65] and Safari.[66] Plugins, such as video players, Adobe Flash, and the wide range of ActiveX
ActiveX
controls enabled by default in Microsoft
Microsoft
Internet Explorer, may also have flaws exploitable via JavaScript
JavaScript
(such flaws have been exploited in the past).[67][68] In Windows Vista, Microsoft
Microsoft
has attempted to contain the risks of bugs such as buffer overflows by running the Internet Explorer
Internet Explorer
process with limited privileges.[69] Google
Google
Chrome similarly confines its page renderers to their own "sandbox". Sandbox implementation errors[edit] Web browsers are capable of running JavaScript
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
JavaScript
from the Web has played a role in vulnerabilities in both Internet Explorer[70] and Firefox.[71] In Windows XP Service Pack 2, Microsoft
Microsoft
demoted JScript's privileges in Internet Explorer.[72] Microsoft
Microsoft
Windows allows JavaScript
JavaScript
source files on a computer's hard drive to be launched as general-purpose, non-sandboxed programs (see: Windows Script Host). This makes JavaScript
JavaScript
(like VBScript) a theoretically viable vector for a Trojan horse, although JavaScript Trojan horses are uncommon in practice.[73][not in citation given] Hardware vulnerabilities[edit] In 2015, a JavaScript-based proof-of-concept implementation of a rowhammer attack was described in a paper by security researchers.[74][75][76][77] In 2017, a JavaScript-based attack via browser was demonstrated that could bypass ASLR. It's called "ASLR⊕Cache" or AnC.[78][79] Uses outside Web pages[edit] In addition to Web browsers and servers, JavaScript
JavaScript
interpreters are embedded in a number of tools. Each of these applications provides its own object model that provides access to the host environment. The core JavaScript
JavaScript
language remains mostly the same in each application. Embedded scripting language[edit]

Google's Chrome extensions, Opera's extensions, Apple's Safari 5 extensions, Apple's Dashboard Widgets, Microsoft's Gadgets, Yahoo! Widgets, Google
Google
Desktop Gadgets, and Serence
Serence
Klipfolio
Klipfolio
are implemented using JavaScript. The MongoDB
MongoDB
database accepts queries written in JavaScript. MongoDB and NodeJS
NodeJS
are the core components of MEAN: a solution stack for creating Web applications using just JavaScript. The Clusterpoint database accept queries written in JS/SQL, which is a combination of SQL and JavaScript. Clusterpoint has built-in computing engine that allows execution of JavaScript
JavaScript
code right inside the distributed database. Adobe's Acrobat and Adobe Reader support JavaScript
JavaScript
in PDF files.[80] Tools in the Adobe Creative Suite, including Photoshop, Illustrator, Dreamweaver, and InDesign, allow scripting through JavaScript. OpenOffice.org, an office application suite, as well as its popular fork LibreOffice, allows JavaScript
JavaScript
to be used as a scripting language. The visual programming language Max, released by Cycling '74, offers a JavaScript
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.[81] The Unity game engine supports a modified version of JavaScript
JavaScript
for scripting via Mono.[82] DX Studio
DX Studio
(3D engine) uses the SpiderMonkey implementation of JavaScript
JavaScript
for game and simulation logic.[83] Maxwell Render (rendering software) provides an ECMA standard based scripting engine for tasks automation.[84] Google
Google
Apps Script in Google
Google
Spreadsheets and Google
Google
Sites allows users to create custom formulas, automate repetitive tasks and also interact with other Google
Google
products such as Gmail.[85] Many IRC clients, like ChatZilla
ChatZilla
or XChat, use JavaScript
JavaScript
for their scripting abilities.[86][87] RPG Maker
RPG Maker
MV uses JavaScript
JavaScript
as its scripting language.[88] The text editor UltraEdit
UltraEdit
uses JavaScript
JavaScript
1.7 as internal scripting language, introduced with version 13 in 2007.

Scripting engine[edit]

Microsoft's Active Scripting technology supports JScript as a scripting language.[89] Java introduced the javax.script package in version 6 that includes a JavaScript
JavaScript
implementation based on Mozilla
Mozilla
Rhino. 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 Document Object Model
Document Object Model
(DOM).[90][91] The Qt C++
C++
toolkit includes a QtScript module to interpret JavaScript, analogous to Java's javax.script package.[92] OS X Yosemite
OS X Yosemite
introduced JavaScript for Automation
JavaScript for Automation
(JXA), which is built upon JavaScriptCore
JavaScriptCore
and the Open Scripting Architecture. It features an Objective-C bridge that enables entire Cocoa applications to be programmed in JavaScript. Late Night Software's JavaScript OSA (also known as JavaScript
JavaScript
for OSA, or JSOSA) is a freeware alternative to AppleScript
AppleScript
for OS X. It is based on the Mozilla
Mozilla
JavaScript
JavaScript
1.5 implementation, with the addition of a MacOS object for interaction with the operating system and third-party applications.

Application platform[edit]

ActionScript, the programming language used in Adobe Flash, is another implementation of the ECMAScript standard. Adobe AIR
Adobe AIR
(Adobe Integrated Runtime) is a JavaScript
JavaScript
runtime that allows developers to create desktop applications. Electron is an open-source framework developed by GitHub. CA Technologies
CA Technologies
AutoShell cross-application scripting environment is built on the SpiderMonkey JavaScript
JavaScript
engine. It contains preprocessor-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. Apache Cordova
Apache Cordova
is a mobile application development framework Cocos2d is an open source software framework. It can be used to build games, apps and other cross platform GUI based interactive programs Chromium Embedded Framework (CEF) is an open source framework for embedding a web browser engine based on the Chromium core RhoMobile Suite
RhoMobile Suite
is a set of development tools for creating data-centric, cross-platform, native mobile consumer and enterprise applications. NW.js call all Node.js
Node.js
modules directly from DOM and enable a new way of writing applications with all Web technologies.[93] GNOME
GNOME
Shell, the shell for the GNOME
GNOME
3 desktop environment,[94] made JavaScript
JavaScript
its default programming language in 2013.[95] The Mozilla application framework (XPFE) platform, which underlies Firefox, Thunderbird, and some other Web browsers, uses JavaScript
JavaScript
to implement the graphical user interface (GUI) of its various products. Qt Quick's markup language (available since Qt 4.7) uses JavaScript for its application logic. Its declarative syntax is also similar to JavaScript. Ubuntu Touch
Ubuntu Touch
provides a JavaScript
JavaScript
API for its unified usability interface. Open webOS
Open webOS
is the next generation of web-centric platforms built to run on a wide range of form factors.[96] enyo JS is a framework to develop apps for all major platforms, from phones and tablets to PCs and TVs[97] WinJS provides a special Windows Library for JavaScript
JavaScript
functionality in Windows 8
Windows 8
that enables the development of Modern style (formerly Metro style) applications in HTML5
HTML5
and JavaScript. NativeScript
NativeScript
is an open-source framework to develop apps on the Apple iOS and Android platforms. Weex is a framework for building Mobile cross-platform UI, created by China Tech giant Alibaba[98] XULRunner is packaged version of the Mozilla
Mozilla
platform to enable standalone desktop application development

Development tools[edit] 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 DOM), it is useful to have access to a debugger for each of the browsers that a Web application targets.[99] Script debuggers are integrated within Internet Explorer, Firefox, Safari, Google
Google
Chrome, Opera and Node.js.[100][101][102] In addition to the native Internet Explorer
Internet Explorer
Developer Tools, three debuggers are available for Internet Explorer: Microsoft
Microsoft
Visual Studio is the richest of the three, closely followed by Microsoft
Microsoft
Script Editor (a component of Microsoft
Microsoft
Office),[103] and finally the free Microsoft
Microsoft
Script Debugger
Debugger
that is far more basic than the other two. The free Microsoft
Microsoft
Visual Web Developer Express provides a limited version of the JavaScript
JavaScript
debugging functionality in Microsoft
Microsoft
Visual Studio. Internet Explorer
Internet Explorer
has included developer tools since version 8. In comparison to Internet Explorer, Firefox
Firefox
has a more comprehensive set of developer tools, which include a debugger as well. Old versions of Firefox
Firefox
without these tools used a Firefox
Firefox
addon called Firebug, or the older Venkman debugger. Also, WebKit's Web Inspector
Web Inspector
includes a JavaScript
JavaScript
debugger,[104] which is used in Safari. A modified version called Blink DevTools is used in Google
Google
Chrome. Node.js
Node.js
has Node Inspector, an interactive debugger that integrates with the Blink DevTools, available in Google
Google
Chrome. Opera includes a set of tools called Dragonfly.[105] In addition to the native computer software, there are online JavaScript
JavaScript
IDEs, debugging aids that are themselves written in JavaScript
JavaScript
and built to run on the Web. An example is the program JSLint, developed by Douglas Crockford
Douglas Crockford
who has written extensively on the language. JSLint scans JavaScript
JavaScript
code for conformance to a set of standards and guidelines. Many libraries for JavaScript, such as three.js, provide links to demonstration code that can be edited by users. They are also used as a pedagogical tool by institutions such as Khan Academy[106] 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[edit] Since JavaScript
JavaScript
is getting more important for web development (frontend overtakes many aspects which were done in backend before), there is also more consideration done about performance. Especially mobile devices could have problems with rendering and processing unoptimized complex logic. A library for doing benchmarks is benchmark.js. A benchmarking library that supports high-resolution timers and returns statistically significant results[citation needed]. Another tool is jsben.ch. An online JavaScript
JavaScript
benchmarking tool, where code snippets can be tested against each other. Version history[edit] See also: ECMAScript § Versions, and ECMAScript § Version correspondence JavaScript
JavaScript
was initially developed in 1996 for use in the Netscape Navigator Web browser. In the same year Microsoft
Microsoft
released an implementation for Internet Explorer. This implementation was called JScript due to trademark issues. In 1997, the first standardized version of the language was released under the name ECMAScript in the first edition of the ECMA-252 standard. The explicit versioning and opt-in of language features was Mozilla-specific and has been removed. Firefox
Firefox
4 was the last version which referred to a JavaScript
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 is based on information from multiple sources.[107][108][109]

Version Release date Equivalent to Netscape Navigator Mozilla Firefox Internet Explorer Opera Safari Google Chrome

Old version, no longer supported: 1.0 March 1996

2.0

3.0

Old version, no longer supported: 1.1 August 1996

3.0

Old version, no longer supported: 1.2 June 1997

4.0-4.05

3

Old version, no longer supported: 1.3 October 1998 ECMA-262 1st + 2nd edition 4.06-4.7x

4.0 5[110]

Old version, no longer supported: 1.4

Netscape Server

6

Old version, no longer supported: 1.5 November 2000 ECMA-262 3rd edition 6.0 1.0 5.5 ( JScript 5.5), 6 ( JScript 5.6), 7 ( JScript 5.7), 8 ( JScript 5.8) 7.0 3.0-5 1.0-10.0.666

Old version, no longer supported: 1.6 November 2005 1.5 + array extras + array and string generics + E4X

1.5

Old version, no longer supported: 1.7 October 2006 1.6 + Pythonic generators + iterators + let

2.0

28.0.1500.95

Old version, no longer supported: 1.8 June 2008 1.7 + generator expressions + expression closures

3.0

11.50

Old version, no longer supported: 1.8.1

1.8 + native JSON
JSON
support + minor updates

3.5

Old version, no longer supported: 1.8.2 June 22, 2009 1.8.1 + minor updates

3.6

Old version, no longer supported: 1.8.5 July 27, 2010 1.8.2 + new features for ECMA-262 5th edition compliance

4.0

Related languages and technologies[edit] JSON, or JavaScript
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
JavaScript
(regexps and anonymous functions as 1st class elements, closures, flexible classes, 'use strict'), JSON, except for replacing Perl's key-value operator '=>' by an RFC 822[111] inspired ':', is syntactically pure Perl. jQuery is a popular JavaScript library designed to simplify DOM-oriented client-side HTML
HTML
scripting along with offering cross-browser compatibility because various browsers respond differently to certain vanilla JavaScript
JavaScript
code. Underscore.js
Underscore.js
is a utility JavaScript library for data manipulation that is used in both client-side and server-side network applications. Angular and AngularJS
AngularJS
are web application frameworks to use for developing single-page applications and also cross-platform mobile apps. React (JavaScript library)
React (JavaScript library)
is an open-source JavaScript
JavaScript
library providing a views that is rendered using components specified as custom HTML
HTML
tags. Mozilla
Mozilla
browsers currently support LiveConnect, a feature that allows JavaScript
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 NP API to the Java 1.6+ plug-in (not yet supported on the Mac as of March 2010[update]).[112] Most browser inspection tools, such as Firebug in Firefox, include JavaScript
JavaScript
interpreters that can act on the visible page's DOM. asm.js is a subset of JavaScript
JavaScript
that can be run in any JavaScript engine or run faster in an ahead-of-time (AOT) compiling engine.[113] JSFuck is an esoteric programming language. Programs are written using only six different characters, but are still valid JavaScript
JavaScript
code. p5.js[114] is an object oriented JavaScript library designed for artists and designers. It is based on the ideas of the Processing project but is for the web. jsben.ch is an online JavaScript
JavaScript
benchmarking tool, where different code snippets can be tested against each other. CRISP: A Strategy guiding Cloud Application Development for Beginners is a strategy proposed by Ayush Sahu to develop optimized and secure JavaScript
JavaScript
application to be used in mobiles, PC's and other devices. CRISP (Conversion, Reformat code, Isolate module, Sandbox, Partition) strategy has been proposed for refined conversion of native application to JavaScript
JavaScript
for cloud application development. JavaScript
JavaScript
is chosen as medium for writing application because it is mostly used language among developers and provides rich API (Application Programming Interface) for writing applications.[115] Use as an intermediate language[edit] As JavaScript
JavaScript
is the most widely supported client-side language that can run within a Web browser, it has become an intermediate language for other languages to target. This has included both newly created languages and ports of existing languages. Some of these include:

OberonScript, a full implementation of the Oberon programming language that compiles to high-level JavaScript.[116] Objective-J, a superset of JavaScript
JavaScript
that compiles to standard JavaScript. It adds traditional inheritance and Smalltalk/Objective-C style dynamic dispatch and optional pseudo-static typing to JavaScript. Processing.js, a JavaScript
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. CoffeeScript, an alternate syntax for JavaScript
JavaScript
intended to be more concise and readable. It adds features like array comprehensions (also available in JavaScript
JavaScript
since version 1.7)[117] and pattern matching. Like Objective-J, it compiles to JavaScript. Ruby and Python have been cited as influential on CoffeeScript
CoffeeScript
syntax. Google
Google
Web Toolkit translates a subset of Java to JavaScript. Scala, an object-oriented and functional programming language, has a Scala-to- JavaScript
JavaScript
compiler.[118] Pyjs, a port of Google
Google
Web Toolkit to Python translates a subset of Python to JavaScript. Google
Google
Dart, an all-purpose, open source language that compiles to JavaScript. Whalesong,[119] a Racket-to- JavaScript
JavaScript
compiler. Emscripten, a LLVM-backend for porting native libraries to JavaScript, known as asm.js[120] Fantom a programming language that runs on JVM, .NET and JavaScript. TypeScript, a free and open-source programming language developed by Microsoft. It is a superset of JavaScript, and essentially adds support for optional type annotations and some other language extensions such as classes, interfaces and modules. A TS-script compiles into plain JavaScript
JavaScript
and can be executed in any JS host supporting ECMAScript 3 or higher. The compiler is itself written in TypeScript. Elm (programming language)
Elm (programming language)
is a pure functional language for web apps. Unlike handwritten JavaScript, Elm-generated JavaScript
JavaScript
has zero runtime exceptions, a time-traveling debugger, and enforced semantic versioning. Haxe, an open-source high-level multiplatform programming language and compiler that can produce applications and source code for many different platforms including JavaScript. ClojureScript,[121] a compiler for Clojure
Clojure
that targets JavaScript. It is designed to emit JavaScript
JavaScript
code that is compatible with the advanced compilation mode of the Google
Google
Closure optimizing compiler. SqueakJS, a virtual machine and DOM environment for the open-source Squeak
Squeak
implementation of the Smalltalk
Smalltalk
programming language. Free Pascal,[122] a compiler for Pascal that targets JavaScript.

As JavaScript
JavaScript
has unusual limitations – such as no explicit integer type, only double-precision binary floating point – languages that compile to JavaScript
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. JavaScript
JavaScript
and Java[edit] A common misconception is that JavaScript
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 also are both typically sandboxed (when used inside a browser), and JavaScript
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,[123] but the similarities end there. Java and JavaScript
JavaScript
both first appeared in 1995, but Java was developed by James Gosling
James Gosling
of Sun Microsystems, and JavaScript
JavaScript
by Brendan Eich
Brendan Eich
of NetScape Communications. The differences between the two languages are more prominent than their similarities. Java has static typing, while JavaScript's typing is dynamic. Java is loaded from compiled bytecode, while JavaScript
JavaScript
is loaded as human-readable source code. Java's objects are class-based, while JavaScript's are prototype-based. Finally, Java did not support functional programming until Java 8, while JavaScript
JavaScript
has done so from the beginning, being influenced by Scheme. WebAssembly[edit] Starting in 2017, web browsers began supporting WebAssembly, a technology standardized by the W3C. The WebAssembly
WebAssembly
standard specifies a binary format, which can be produced by a compiler toolchain such as LLVM, 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
JavaScript
to author client-side code for the World Wide Web.[124] See also[edit]

Computer programming portal

WebAssembly

References[edit]

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Further reading[edit]

Bhangal, Sham; Jankowski, Tomasz (2003). Foundation Web Design: Essential HTML, JavaScript, CSS, PhotoShop, Fireworks, and Flash. APress L. P. ISBN 1-59059-152-6.  Burns, Joe; Growney, Andree S. (2001). JavaScript
JavaScript
Goodies. Pearson Education. ISBN 0-7897-2612-2.  Duffy, Scott (2003). How to do Everything with JavaScript. Osborne. ISBN 0-07-222887-3.  Flanagan, David (2006). JavaScript: The Definitive Guide (5th ed.). O'Reilly & Associates. ISBN 0-596-10199-6.  Flanagan, David (2011). JavaScript: The Definitive Guide (6th ed.). O'Reilly & Associates. ISBN 978-0-596-80552-4.  Goodman, Danny; Eich, Brendan (2001). JavaScript
JavaScript
Bible. John Wiley & Sons. ISBN 0-7645-3342-8.  Goodman, Danny; Markel, Scott (2003). JavaScript
JavaScript
and D HTML
HTML
Cookbook. O'Reilly & Associates. ISBN 0-596-00467-2.  Harris, Andy (2001). JavaScript
JavaScript
Programming for the Absolute Beginner. Premier Press. ISBN 0-7615-3410-5.  Haverbeke, Marijn (2011). Eloquent JavaScript. No Starch Press. ISBN 978-1-59327-282-1.  Heinle, Nick; Koman, Richard (1997). Designing with JavaScript. O'Reilly & Associates. ISBN 1-56592-300-6.  Husted, Robert; Kuslich, JJ (1999). Server-Side JavaScript: Developing Integrated Web Applications (1st ed.). Addison-Wesley. ISBN 0-201-43329-X.  McDuffie, Tina Spain (2003). JavaScript
JavaScript
Concepts & Techniques: Programming Interactive Web Sites. Franklin, Beedle & Associates. ISBN 1-887902-69-4.  McFarlane, Nigel (2003). Rapid Application Development with Mozilla. Prentice Hall Professional Technical References. ISBN 0-13-142343-6.  Powell, Thomas A.; Schneider, Fritz (2001). JavaScript: The Complete Reference. McGraw-Hill Companies. ISBN 0-07-219127-9.  Shelly, Gary B.; Cashman, Thomas J.; Dorin, William J.; Quasney, Jeffrey J. (2000). JavaScript: Complete Concepts and Techniques. Cambridge: Course Technology. ISBN 0-7895-6233-2.  Vander Veer, Emily A. (2004). JavaScript
JavaScript
For Dummies (4th ed.). Wiley Pub. ISBN 0-7645-7659-3.  Watt, Andrew H.; Watt, Jonathan A.; Simon, Jinjer L. (2002). Teach Yourself JavaScript
JavaScript
in 21 Days. Pearson Education. ISBN 0-672-32297-8.  Zakas, Nicholas C. (2012). Professional JavaScript
JavaScript
for Web Developers (3rd ed.). Wrox. ISBN 978-1-118-02669-4. 

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