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ECMAScript
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ECMAScript is a scripting language, standardized by Ecma International in the ECMA-262 specification. The language is widely used on the web, and is often confused with JavaScript or JScript, the two major dialects from which ECMAScript was standardized.
lass="link1" onMouseover='showByLink("m861619",this)' onMouseout='hide("m861619")'href="http://www.absoluteastronomy.com/topics/JavaScript">JavaScript was originally developed by Brendan Eich of Netscape under the name Mocha, later LiveScript, and finally renamed to JavaScript. In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release.
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Encyclopedia
ECMAScript is a scripting language, standardized by Ecma International in the ECMA-262 specification. The language is widely used on the web, and is often confused with JavaScript or JScript, the two major dialects from which ECMAScript was standardized.
History
JavaScript was originally developed by Brendan Eich of Netscape under the name Mocha, later LiveScript, and finally renamed to JavaScript. In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release. In March 1996 Netscape Navigator 2.0 was out, featuring support for JavaScript.
Due to the wide-spread success of JavaScript as a client-side scripting language for web pages, Microsoft developed a compatible dialect of the language, naming it JScript to avoid trademark issues. JScript added new date methods to fix the non-Y2K-friendly methods in JavaScript, which were based on . JScript was included in Internet Explorer 3.0, released in August 1996.
Netscape submitted JavaScript to Ecma International for standardization; the work on the specification, ECMA-262, began in November 1996. The first edition of ECMA-262 was adopted by the ECMA General Assembly of June 1997.
ECMAScript is the name of the scripting language standardized in ECMA-262. Both JavaScript and JScript aim to be compatible with ECMAScript, while providing additional features not described in the ECMA specification.
The name "ECMAScript" was a compromise between the organizations involved in standardizing the language, especially Netscape and Microsoft. Brendan Eich, the creator of JavaScript, is on record as saying that "ECMAScript was always an unwanted trade name that sounds like a skin disease."
Versions
There are three editions of ECMA-262 published. Work on a revision to the third edition known as "ECMAScript 3.1", and on a future edition codenamed "Harmony", is in progress.
| Edition | Date published | Differences to the previous edition | Editor |
|---|
| 1 | June 1997 | First edition | Guy L. Steele, Jr. | | 2 | June 1998 | Editorial changes to keep the specification fully aligned with ISO/IEC 16262 international standard | Mike Cowlishaw | | 3 | December 1999 | Added regular expressions, better string handling, new control statements, try/catch exception handling, tighter definition of errors, formatting for numeric output and other enhancements | Mike Cowlishaw | | 3.1 | Work in progress | Adds "strict mode", a subset intended to provide more thorough error checking and avoid error-prone constructs. Clarifies many ambiguities in the 3rd edition specification, and accomodates behaviour of real-world implementations that differed consistently from that specification. Adds some new features, such as getters and setters, library support for JSON, and more complete reflection on object properties. | | | Harmony | Work in progress | Multiple new concepts and language features — see the section "Future development" below. | |
In June 2004 Ecma International published ECMA-357 standard, defining an extension to ECMAScript, known as E4X (ECMAScript for XML).
ECMA also defined a "Compact Profile" for ECMAScript — known as ES-CP, or ECMA 327 — which is designed for resource-constrained devices. Several of the dynamic features of ECMAScript (such as the "eval" function) are made optional, thus allowing the runtime to make more assumptions about the behaviour of programs and therefore make more performance trade-offs when running the code. The HD DVD standard is one place where the ECMAScript Compact Profile is used in favour of full ECMAScript in order to reduce processing and memory requirements on a device.
Features
The ECMAScript language includes structured, dynamic, functional, and prototype-based features.
Syntax
Dialects
ECMAScript is supported in many applications, especially web browsers, where it is commonly called JavaScript. Dialects sometimes include extensions to the language, or to the standard library and related APIs such as the W3C-specified DOM. This means that applications written in one dialect may be incompatible with another, unless they are written to use only a common subset of supported features and APIs.
Note that there is a distinction between a dialect and an implementation. A dialect of a language is significant variation of the language, while an implementation of a language/dialect executes a program written in that dialect.
| Application | Dialect and latest version | ECMAScript edition |
|---|
| Google Chrome, the V8 engine | JavaScript | ECMA-262, edition 3 9 | | Mozilla Firefox, the Gecko layout engine, SpiderMonkey, and Rhino 6 | JavaScript 1.8 | ECMA-262, edition 3 | | Internet Explorer, the Trident layout engine | JScript 5.7 | ECMA-262, edition 3 | | Opera | ECMAScript with some JavaScript 1.5
and JScript extensions | ECMA-262, edition 3 | | KHTML layout engine, KDE's Konqueror, and Apple's Safari7 | JavaScript 1.5 1 | ECMA-262, edition 3 5 | | , Samba 4 | 0.9.5 | ECMA-262, edition 3 8 | | Microsoft .NET Framework | JScript .NET 8.0 | ECMA-262, edition 3 2 | | Adobe Flash and Adobe Flex | ActionScript 3 | ECMA-262, edition 3 3 | | Adobe Acrobat | JavaScript 1.5 1 | ECMA-262, edition 3 | | General purpose scripting language | 1.06 | ECMA-262 | | OpenLaszlo Platform | JavaScript 1.4 1 | ECMA-262, edition 3 4 | | , JScript for game platforms | 0.9.0 | ECMA-262, edition 3 | | iCab | InScript 3.22 | ECMA-262, edition 3 | | Max/MSP | JavaScript 1.5 1 | ECMA-262, edition 3 | | ANT Galio with Venturi layout engine and SpiderPig | JavaScript 1.5 1 with RMAI extensions | ECMA-262, edition 3 |
Note (1): Mozilla manages the official version of JavaScript. Most non-Mozilla implementations claiming JavaScript "compliance" do not actually support most JavaScript extensions; rather, they target ECMA-262, edition 3.
Note (2): Microsoft asserts that JScript 8.0 supports "almost all of the features of the ECMAScript Edition 3 Language Specification" but does not list the unsupported features.
Note (3): In addition to supporting ECMA-262 edition 3, ActionScript 3 also included support for extensions proposed in drafts of ECMAScript edition 4.
Note (4): As of version 4, OpenLaszlo implements standard ECMAScript edition 3 with some extensions proposed in drafts of ECMAScript edition 4
Note (5): The current WebKit binaries, as of April 2007, also implement at least part of the Javascript 1.6 extras
Note (6): The Mozilla implementations, (SpiderMonkey in the C programming language and Rhino in the Java programming language), are used in several third-party programs, including the Yahoo! Widget Engine (Konfabulator) and the Macintosh system-level scripting language JavaScript OSA.
Note (7): Apple's Safari uses JavaScriptCore which is based on the KDE KJS library.
Note (8): This implementation was asserted to support some extensions proposed in drafts of ECMAScript edition 4
Note (9): V8 implements ECMAScript as specified in ECMA-262, 3rd edition.
Version correspondence
The following table is based on and ; items on the same line are approximately the same language.
| JavaScript | JScript | ECMAScript |
|---|
| 1.0 (Netscape 2.0, March 1996) | 1.0 (IE 3.0 - early versions, August 1996) | | | 1.1 (Netscape 3.0, August 1996) | 2.0 (IE 3.0 - later versions, January 1997) | | | 1.2 (Netscape 4.0-4.05, June 1997) | | | | 1.3 (Netscape 4.06-4.7x, October 1998) | 3.0 (IE 4.0, Oct 1997) | Edition 1 (June 1997) / Edition 2 (June 1998) | | 1.4 (Netscape Server only) | 4.0 (Visual Studio 6, no IE release) | | | | 5.0 (IE 5.0, March 1999) | | | | 5.1 (IE 5.01) | | 1.5 (Netscape 6.0, Nov 2000; also
later Netscape and Mozilla releases) | 5.5 (IE 5.5, July 2000) | Edition 3 (December 1999) | | | 5.6 (IE 6.0, October 2001) | | | 1.6 (Gecko 1.8, Firefox 1.5, November 2005) | | Edition 3, with some compliant enhancements: E4X, Array extras (e.g. Array.prototype.forEach), Array and String generics () | | 1.7 (Gecko 1.8.1, Firefox 2, October 2006) | | Edition 3 plus all JavaScript 1.6 enhancements, plus Pythonic generators and array comprehensions ([a*a for (a in iter)]), block scope with let, destructuring assignment (var [a,b]=[1,2]) () | | 1.8 (Gecko 1.9, Firefox 3, June 2008) | | Edition 3 plus all JavaScript 1.7 enhancements, plus expression closures (function(x) x * x), generator expressions, and more () | | | JScript .NET (ASP.NET; no IE release) | | | JavaScript 2.0 (Work in progress) | | Harmony (Work in progress; see the section "ECMAScript Harmony" below). |
Future development
The proposed fourth edition of ECMA-262 (ECMAScript 4 or ES4) would have been the first major update to ECMAScript since the third edition was published in 1999. The specification (along with a reference implementation) was originally targeted for completion by October 2008. An of the language was released by the working group on October 22, 2007.
As of August 2008, the ECMAScript 4th edition proposal has been scaled back into a project codenamed ECMAScript Harmony.
Features
Features under discussion for a future edition (originally "ECMAScript 4"; now ECMAScript Harmony) include:
The intent of these features is partly to better support "programming in the large", and to let programmers sacrifice some of the script's ability to be dynamic for performance. For example, Tamarin — the virtual machine for ActionScript developed and open sourced by Adobe — has JIT compilation support for certain classes of scripts.
Bug fixes and backwards compatibility
In addition to introducing new features, some ES3 bugs were proposed to be fixed in edition 4. . These fixes and others, and support for JSON encoding/decoding, have now been folded into the ECMAScript 3.1 specification.
History
Work started on Edition 4 after the ES-CP (Compact Profile) specification was completed, and continued for approximately 18 months where slow progress was made balancing the theory of Netscape's JavaScript 2 specification with the implementation experience of Microsoft's JScript .NET. After some time, the focus shifted to the E4X standard.
The update has not been without controversy. In late 2007, a debate between Eich, now the Mozilla Foundation's CTO, and Chris Wilson, Microsoft's platform architect for Internet Explorer, became public on a number of blogs. Wilson cautioned that because the proposed changes to ECMAScript made it backwards incompatible in some respects to earlier versions of the language, the update amounted to "breaking the Web," and that stakeholders who opposed the changes were being "hidden from view". Eich responded by stating that Wilson seemed to be "repeating falsehoods in blogs" and denied that there was attempt to suppress dissent and challenging critics to give specific examples of incompatibility. He also pointed out that Microsoft Silverlight and Adobe AIR rely on C# and ActionScript 3 respectively, both of which are larger and more complex than ECMAScript Edition 3.
ECMAScript 3.1
Microsoft, Yahoo, and other 4th edition dissenters formed their own subcommittee to design a less ambitious update of ECMAScript 3, tentatively named ECMAScript 3.1. This edition would focus on security and library updates with a large emphasis on compatibility. After the aforementioned public sparring, the ECMAScript 3.1 and ECMAScript 4 teams agreed on a compromise: the two editions would be worked on in parallel, with coordination between the teams to ensure that ECMAScript 3.1 remains a strict subset of ECMAScript 4 in both semantics and syntax.
However, the differing philosophies in each team resulted in repeated breakages of the subset rule, and it remained doubtful that the ECMAScript 4 dissenters would ever support or implement ECMAScript 4 in the future. After over a year since the disagreement over the future of ECMAScript within the ECMA Technical Committee 39, the two teams reached a new compromise: ECMA TC39 announced it would focus work on the ECMAScript 3.1 project with full collaboration of all parties, and it would target two interoperable implementations by early 2009.
ECMAScript Harmony
In the same announcement, ECMA TC39 also stated that the ECMAScript 4 proposal would be superseded by a new project, code-named ECMAScript Harmony. ECMAScript Harmony will include syntactic extensions, but the changes will be more modest than ECMAScript 4 in both semantic and syntactic innovation. Packages, namespaces and early binding from ECMAScript 4 are no longer included for planned releases. In addition, other goals and ideas from ECMAScript 4 are being rephrased to keep consensus in the committee; these include a notion of classes based on existing ECMAScript 3 concepts combined with proposed ECMAScript 3.1 extensions. As of August 2008, there is no publicly announced release date for ECMAScript Harmony. Depending on how ECMAScript 3.1 is officially named, ECMAScript Harmony may end up being the new ECMAScript 4th edition.
See also
External links
- : John Resig's map on ECMAScript
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