JavaScript (/ˈdʒɑːvəˌskrɪpt/),^[8] often abbreviated as JS, is a high-level, interpreted scripting language that conforms to the ECMAScript specification. JavaScript has curly-bracket syntax, dynamic typing, prototype-based object-orientation, and first-class functions.

Alongside HTML and CSS, JavaScript is one of the core technologies of the World Wide Web.^[9] JavaScript enables interactive web pages and is an essential part of web applications. The vast majority of websites use it,^[10] and major web browsers have a dedicated JavaScript engine to execute it.

As a multi-paradigm language, JavaScript supports event-driven, functional, and imperative (including object-oriented and prototype-based) programming styles. It has APIs for working with text, arrays, dates, regular expressions, and the DOM, but the language itself does not include any I/O, such as networking, storage, or graphics facilities. It relies upon the host environment in which it is embedded to provide these features.

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 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.^[11][12]

Although there are similarities between JavaScript and Java, including language name, syntax, and respective standard libraries, the two languages are distinct and differ greatly in design. JavaScript was influenced by programming languages such as Self and Scheme.^[13] The JSON serialization format, used to store data structures in files or transmit them across networks, is based on JavaScript.^[14]

In 1993, the 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 beyond the NeXTSTEP niche where the WorldWideWeb had formed three years earlier. In 1994, a company called Mosaic Communications was founded in 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, a portmanteau of "Mosaic and Godzilla".^[15] 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. Marc Andreessen, the founder of the company, believed that 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 Communications recruited Brendan Eich with the goal of embedding the Scheme programming language into its Netscape Navigator.^[16] Before he could get started, Netscape Communications collaborated with Sun Microsystems to include Sun's more static programming language, Java, in Netscape Navigator so as to compete with Microsoft for user adoption of Web technologies and platforms.^[17] 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 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.^[2][18] 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^[19] 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 Nombas named Cmm (not to be confused with the later C-- created in 1997).^[20][21] 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 ViolaWWW Web browser.^[22] Nombas later switched to offering JavaScript instead of Cmm in their ScriptEase product and was part of the TC39 group that standardized ECMAScript.^[23]

In December 1995, soon after releasing JavaScript for browsers, Netscape introduced an implementation of the language for server-side scripting with Netscape Enterprise Server.^[24]

Since 1996, the IIS web-server has supported Microsoft's implementation of server-side Javascript—JScript—in ASP and .NET pages.^[25]

Since the mid-2000s, additional server-side JavaScript implementations have been introduced, such as Node.js in 2009.^[26]

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 3. JScript was also available for server-side scripting in Internet Information Server. 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.^[27][28] 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.^[29] 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.^[27] With the release of Internet Explorer 4, 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 on the Web.^[27]

In November 1996, Netscape submitted 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 being the most well known of the implementations. ActionScript and JScript were other well-known implementations of ECMAScript.

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 Google) started in 2000. Microsoft initially participated and implemented some proposals in their JScript .NET 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 .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 and Mozilla rejoined Ecma International as a not-for-profit member and work started on ECMAScript for XML (E4X), the ECMA-357 standard, which came from ex-Microsoft employees at BEA Systems (originally acquired as Crossgain). This led to working jointly with Macromedia (later acquired by Adobe Systems), 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 Tamarin, as an open source 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; Douglas Crockford—then at Yahoo!—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.^[30]

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 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 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]

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".^[31] The advent of Ajax returned JavaScript to the spotlight and brought more professional programming attention. The result was a proliferation of comprehensive frameworks and libraries, improved JavaScript programming practices, and increased usage of JavaScript outside Web browsers, as seen by the proliferation of Server-side JavaScript platforms.

In January 2009, the CommonJS project was founded with the goal of specifying a common standard library mainly for JavaScript development outside the browser.^[32]

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.

"JavaScript" is a trademark of Oracle Corporation in the United States.^[33] It is used under license for technology invented and implemented by Netscape Communications and current entities such as the Mozilla Foundation.^[34]

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

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

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 originally had only function scoping with var. ECMAScript 2015 added keywords let and const for block scoping, meaning JavaScript now has both function and block scoping. Like C, 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.^[35]

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

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().^[43] 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.^[44] JavaScript also supports anonymous functions.

JavaScript supports implicit and explicit delegation.

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

Variables in JavaScript can be defined using either the var,^[54] let^[55] or const^[56] keywords.

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

There is no built-in Input/output functionality in JavaScript; the run-time environment provides that. The ECMAScript specification in edition 5.1 mentions:^[57]

However, most runtime environments have a console object^[58] that can be used to print output. Here is a minimalist Hello World program in JavaScript:

A simple recursive function:

An anonymous function (or lambda):

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

Arrow functions were first introduced in 6th Edition - ECMAScript 2015 . 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, objects are created in the same way as functions; this is known as a function object.

Object example:

Variadic function demonstration (arguments is a special variable):^[59]

Immediately-invoked function expressions 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^[60]

Export example:

Import example:

This sample code displays various JavaScript features.

The following output should be displayed in the browser window.

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

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 Gmail take advantage of this: much of the user-interface logic is written in JavaScript, and JavaScript dispatches requests for information (such as the content of an e-mail message) to the server. The wider trend of Ajax programming similarly exploits this strength.

A JavaScript engine (also known as JavaScript interpreter or JavaScript implementation) is an interpreter that interprets JavaScript source code and executes the script accordingly. The first JavaScript engine was created by Brendan Eich at Netscape, for the Netscape Navigator Web browser. The engine, code-named SpiderMonkey, is implemented in C. It has since been updated (in JavaScript 1.5) to conform to 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 is the most common host environment for JavaScript. However, a Web browser does not have to execute JavaScript code. (For example, text-based browsers have no JavaScript engines; and users of other browsers may disable scripts through a preference or extension.)

A Web browser typically creates "host objects" to represent the DOM in JavaScript. The Web server is another common host environment. A JavaScript Web server would typically expose host objects representing HTTP 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 target language for frameworks in other languages.^[61] The increasing speed of JavaScript engines has made the language a feasible compilation target, despite the performance limitations inherent to its dynamic nature.

Below is a minimal example of a standards-conforming Web page containing JavaScript (using HTML 5 syntax) and the DOM:

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 W3C 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.^[62] Authors may also find it practical to detect what browser is running, as two browsers may implement the same feature with differing behavior.^[63][64] 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:

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 would have added. Some sites use the HTML

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).^[66][67] Caja is another project for safe embedding and isolation of third-party JavaScript and HTML.

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

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 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.^[68]

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 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

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:

Package management systems such as npm and Bower 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.^[71] "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."^[71] 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.^[72][73]

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 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,^[74] Internet Explorer,^[75] and Safari.^[76]

Plugins, such as video players, Adobe Flash, and the wide range of ActiveX controls enabled by default in Microsoft Internet Explorer, may also have flaws exploitable via JavaScript (such flaws have been exploited in the past).^[77][78]

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.^[79] Google Chrome similarly confines its page renderers to their own "sandbox".

Web browsers are capable of running JavaScript outside the sandbox, with the privileges necessary to, for example, create or delete files. 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^[80] and Firefox.^[81] In Windows XP Service Pack 2, Microsoft demoted JScript's privileges in Internet Explorer.^[82]

Microsoft Windows allows 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 (like VBScript) a theoretically viable vector for a Trojan horse, although JavaScript Trojan horses are uncommon in practice.^[83]

In 2015, a JavaScript-based proof-of-concept implementation of a rowhammer attack was described in a paper by security researchers.^{[84][85][86][87]}

In 2017, a JavaScript-based attack via browser was demonstrated that could bypass ASLR. It's called "ASLR⊕Cache" or AnC.^[88][89]

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

Within JavaScript, access to a debugger 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.^[109]

Script debuggers are integrated within many mainstream browsers such as Internet Explorer, Firefox, Safari, Google Chrome, Opera and Node.js.^{[110][111][112]}

In addition to the native Internet Explorer Developer Tools, three other debuggers are available for Internet Explorer: Microsoft Visual Studio has the most features of the three, closely followed by Microsoft Script Editor (a component of Microsoft Office),^[113] and finally the free Microsoft Script Debugger. The free Microsoft Visual Web Developer Express 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 Firefox addon called Firebug, or the older Venkman debugger. WebKit's Web Inspector includes a JavaScript debugger,^[114] which is used in Safari. A modified version called Blink DevTools is used in Google Chrome. Node.js has Node Inspector, an interactive debugger that integrates with the Blink DevTools. Opera includes a set of tools called Dragonfly.^[115]

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 JSLint, developed by Douglas Crockford 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 three.js, provide links to demonstration code that can be edited by users. Demonstration codes are also used as a pedagogical tool by institutions such as Khan Academy^[116] 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.

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

A library for doing benchmarks is benchmark.js.^[117] A benchmarking library that supports high-resolution timers and returns statistically significant results.

Another tool is jsben.ch.^[118] An online JavaScript benchmarking tool, where code snippets can be tested against each other.

JavaScript was initially developed in 1996 for use in the Netscape Navigator Web browser. In the same year 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-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.^{[119][120][121]}

As 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 (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.

A common misconception is that JavaScript is similar or closely related to Java. It is true that both have a C-like syntax (the C language being their most immediate common ancestor language). They also are both typically sandboxed (when used inside a browser), and JavaScript was designed with Java's syntax and standard library in mind. In particular, all Java keywords were reserved in original JavaScript, JavaScript's standard library follows Java's naming conventions, and JavaScript's Math and Date objects are based on classes from Java 1.0,^[134] but the similarities end there.

Java and JavaScript both first appeared in 1995, but Java was developed by James Gosling of Sun Microsystems, and JavaScript by 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 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 has done so from the beginning, being influenced by Scheme.

Starting in 2017, web browsers began supporting WebAssembly, a technology standardized by the W3C. The 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 to author client-side code for the World Wide Web.^[135]