ECMAScript (; ES) is a

JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...

standard intended to ensure the

interoperability Interoperability is a characteristic of a product or system to work with other products or systems. While the term was initially defined for information technology or systems engineering services to allow for information exchange, a broader defi ...

of web pages across different browsers. It is standardized by

Ecma International Ecma International () is a nonprofit standards organization for information and communication systems. It acquired its current name in 1994, when the European Computer Manufacturers Association (ECMA) changed its name to reflect the organization ...

in the documen
ECMA-262
ECMAScript is commonly used for

client-side scripting A server-side dynamic web page is a web page whose construction is controlled by an application server processing server-side scripts. In server-side scripting, parameters determine how the assembly of every new web page proceeds, and includi ...

on the

World Wide Web The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet. Documents and downloadable media are made available to the network through web ...

, and it is increasingly being used for writing server-side applications and services using Node.js and other runtime environments.

ECMAScript, ECMA-262 and JavaScript

ECMA-262, or the ''ECMAScript Language Specification'', defines the ''ECMAScript Language'', or just ECMAScript. ECMA-262 specifies only language syntax and the semantics of the core API, such as , , and , while valid implementations of JavaScript add their own functionality such as input-output and file-system handling.

History

The ECMAScript specification is a standardized specification of a scripting language developed by

Brendan Eich Brendan Eich (; born July 4, 1961) is an American computer programmer and technology executive. He created the JavaScript programming language and co-founded the Mozilla project, the Mozilla Foundation, and the Mozilla Corporation. He served ...

of Netscape; initially named Mocha, then LiveScript, and finally JavaScript. In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release. In November 1996, Netscape announced a meeting of the

standards organization to advance the standardization of JavaScript. The first edition of ECMA-262 was adopted by the Ecma General Assembly in June 1997. Several editions of the language standard have been published since then. The name "ECMAScript" was a compromise between the organizations involved in standardizing the language, especially Netscape and Microsoft, whose disputes dominated the early standards sessions. Eich commented that "ECMAScript was always an unwanted trade name that sounds like a

skin disease A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this ...

." ECMAScript has been formalized through

operational semantics Operational semantics is a category of formal programming language semantics in which certain desired properties of a program, such as correctness, safety or security, are verified by constructing proofs from logical statements about its execut ...

by work at Stanford University and the Department of Computing,

Imperial College London Imperial College London (legally Imperial College of Science, Technology and Medicine) is a public research university in London, United Kingdom. Its history began with Prince Albert, consort of Queen Victoria, who developed his vision for a cu ...

for security analysis and standardization.

Version history

Features

The ECMAScript language includes

structured Structuring, also known as smurfing in banking jargon, is the practice of executing financial transactions such as making bank deposits in a specific pattern, calculated to avoid triggering financial institutions to file reports required by law ...

, dynamic, functional, and prototype-based features.

Imperative and structured

ECMAScript JavaScript supports C style structured programming. Previously, JavaScript only supported

function scoping In computer programming, the scope of a name binding (an association of a name to an entity, such as a variable) is the part of a program where the name binding is valid; that is, where the name can be used to refer to the entity. In other parts ...

using the keyword var, but ECMAScript 2015 added the keywords let and const allowing JavaScript to support both block scoping and function scoping. JavaScript supports

automatic semicolon insertion In computer science, lexical analysis, lexing or tokenization is the process of converting a sequence of characters (such as in a computer program or web page) into a sequence of ''lexical tokens'' ( strings with an assigned and thus identified ...

, meaning that semicolons that are normally used to terminate a statement in C may be omitted in JavaScript. Like C-style languages, control flow is done with the , , / , / , and statements. Functions are weakly typed and may accept and return any type. Arguments not provided default to .

Weakly typed

ECMAScript is weakly typed. This means that certain types are assigned implicitly based on the operation being performed. However, there are several quirks in JavaScript's implementation of the conversion of a variable from one type to another. These quirks have been the subject of a talk entitled ''Wat''.

Dynamic

ECMAScript is dynamically typed. Thus, a type is associated with a value rather than an expression. ECMAScript supports various ways to test the type of objects, including

duck typing Duck typing in computer programming is an application of the duck test—"If it walks like a duck and it quacks like a duck, then it must be a duck"—to determine whether an object can be used for a particular purpose. With nominative ty ...

Transpiling

Since ES 2015, transpiling JavaScript has become very common. Transpilation is a source-to-source compilation in which newer versions of JavaScript are used, and a transpiler rewrites the source code so that it is supported by older browsers. Usually, transpilers transpile down to ES3 to maintain compatibility with all versions of browsers. The settings to transpiling to a specific version can be configured according to need. Transpiling adds an extra step to the build process and is sometimes done to avoid needing polyfills. Polyfills create new features for older environments that lack them. Polyfills do this at runtime in the interpreter, such as the user's browser or on the server. Instead, transpiling rewrites the ECMA code itself during the build phase of development before it reaches the interpreter.

Conformance

In 2010, Ecma International started developing a standards test for Ecma 262 ECMAScript. Test262 is an ECMAScript conformance test suite that can be used to check how closely a JavaScript implementation follows the ECMAScript Specification. The test suite contains thousands of individual tests, each of which tests some specific requirement(s) of the ECMAScript specification. The development of Test262 is a project of the Ecma Technical Committee 39 (TC39). The testing framework and individual tests are created by member organizations of TC39 and contributed to Ecma for use in Test262. Important contributions were made by Google (Sputnik testsuite) and Microsoft who both contributed thousands of tests. The Test262 testsuite consisted of tests . ECMAScript specifications through ES7 are well-supported in major web browsers. The table below shows the conformance rate for current versions of software with respect to the most recent editions of ECMAScript.

References

{{List of International Electrotechnical Commission standards Computer-related introductions in 1997 C programming language family Computer standards Dynamically typed programming languages Ecma standards JavaScript dialect engines JavaScript programming language family Object-based programming languages Programming languages with an ISO standard Prototype-based programming languages Scripting languages Source-to-source compilers