ECMAScript

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ECMAScript
Paradigm multi-paradigm: prototype-oriented, functional, imperative, scripting
Appeared in 1997
Designed by Brendan Eich, Ecma International
Typing discipline duck, weak, dynamic
Dialects JavaScript, ActionScript, JScript, QtScript, JScript .NET, DMDScript, InScript
Influenced by Self, HyperTalk, AWK, C, Perl, Python, Java
ECMAScript
File name extension .es
Internet media type application/ecmascript[1]

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 referred to as JavaScript or JScript, after the two primary dialects of the specification.

Contents

[edit] 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[2]. 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 language known as JScript. JScript added new date methods to fix the Y2K non-compliant methods in JavaScript, which were based on java.util.Date. 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[3]. The first edition of ECMA-262 was adopted by the ECMA General Assembly of June 1997[4].

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."[5]

[edit] Versions

There are three editions of ECMA-262 published, and the work on the fourth edition is in progress.

Edition Date published Differences to the previous edition
1 June 1997 First edition, editor Guy L. Steele, Jr.
2 June 1998 Editorial changes to keep the specification fully aligned with ISO/IEC 16262 international standard; editor 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; editor Mike Cowlishaw.
4 Work in progress Multiple new concepts and language features — see the section "Fourth edition" 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.

[edit] Features

Further information: ECMAScript features

ECMAScript is dynamic and structured.

[edit] Syntax

Further information: ECMAScript syntax

[edit] Dialects

ECMAScript is supported in many applications, especially web browsers, where it is commonly called JavaScript. Dialects typically include their own, different standard libraries, of which some are standardized separately — such as the W3C-specified DOM. Some implementations, such as ActionScript used in Flash, have a completely different set of libraries. This means that applications written in one dialect of ECMAScript will not likely work in another, unless they are designed to be compatible.

Application Dialect Latest dialect version Corresponding ECMAScript edition
Mozilla Firefox7, the Gecko layout engine, SpiderMonkey, and Rhino JavaScript 1.7 ECMA-262, edition 3 1
Internet Explorer JScript 5.7 ECMA-262, edition 3
Opera ECMAScript, with extensions to both JavaScript and JScript 1.3/1.5 ECMA-262, edition 3
KHTML layout engine, KDE's Konqueror, and Apple's Safari8 JavaScript 1.5 6 ECMA-262
Microsoft .NET Framework JScript .NET 8.0 ECMA-262, edition 3 2
Adobe Flash and Adobe Flex ActionScript 2

3

 ECMA-262, edition 3 3

ECMA-262, edition 4 4
Adobe Acrobat JavaScript 1.5 ECMA-262, edition 3
General purpose scripting language DMDScript 1.06 ECMA-262
OpenLaszlo Platform JavaScript 1.4 ECMA-262, edition 3 5
CriScript, JScript for game platforms CriScript 0.9.0 ECMA-262, edition 3
iCab InScript 3.22 ECMA-262, edition 3
Max/MSP JavaScript 1.5 ECMA-262, edition 3
Samba 4 and embedded servers. (ASCII only, no floats; removes: try catch throw break continue switch while do with === !== <<< >>>, prefix ++ --, regular expressions, array and object literals, Number, Date, Regex, various methods) Embedded JavaScript ? ECMA-262

Note (1): Gecko 1.8.1 has partial support of E4X (documentation) and a few other features (New in JavaScript 1.7).

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 2 also included support of properties, methods, and mechanisms that were proposed in early draft specifications of as yet unseen versions of ECMAScript. It remains to be seen if ActionScript will stay in sync with future changes to the ECMAScript specifications.

Note (4): Adobe asserts it implements the preliminary edition 4 of ECMA-262 [6]

Note (5): As of version 4, OpenLaszlo implements standard ECMAScript edition 3 with some preliminary ECMAScript edition 4 extensions [7]

Note (6): The current WebKit binaries, as of April 2007, also implement at least part of the Javascript 1.6 extras

Note (7): 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 (8): Apple's Safari uses JavaScriptCore which is based on the KDE KJS library.

[edit] Version correspondence

The following table is based on [1] and [2]; 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 [3]
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]) [4]
1.8 (Gecko 1.9, Firefox 3, in development) Edition 3 plus all JavaScript 1.7 enhancements, plus expression closures (function(x) x * x), generator expressions, and more [5]
JScript .NET (ASP.NET; no IE release) (JScript .NET is said to be designed with the participation of other ECMA members)
JavaScript 2.0 Edition 4 (Work in progress; see the section "Fourth edition" below).

[edit] Fourth edition

The ECMA-262 fourth edition is the first major update to ECMAScript since the third edition published in 1999. The specification (along with the reference implementation) is currently under development and is expected to be finished by October 2008 [6].

An overview of the language was released by the working group on October 22, 2007.

[edit] Features

The new version of the language is mostly backwards compatible with ECMAScript 3 (see below), while adding multiple new features, such as:

ECMAScript 4 intends 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.

[edit] Bug fixes and backwards compatibility

In addition to introducing new features, some ES3 bugs are fixed in edition 4.[8]

A document describing known incompatibilities between ES3 and ES4 is available.

[edit] Implementations

Since the specification is not yet finished, there are no full implementations of the language at this time. However several implementations are in progress:

  • Tamarin, an open-source ECMAScript engine, will implement ES4. Mozilla plans to use Tamarin in Firefox 4.
  • TG1 is working on the reference implementation in SML/NJ and the work-in-progress is available.
  • According to Brendan Eich, there are several other "industry-scale implementations underway".[9]

[edit] 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 as it was less controversial, being only an update to Edition 3.

The upgrade is not without controversy. In late 2007, 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,"[10] and that stakeholders who opposed the changes were being "hidden from view".[11] 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.[12] 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.[13]

[edit] See also

[edit] References

  1. ^ RFC 4329
  2. ^ Press Release
  3. ^ Press Release
  4. ^ Microsoft Word - Ecma-262.doc
  5. ^ Will there be a suggested file suffix for es4?
  6. ^ The Kiwi Project: AS3 language 101 for C/C++ coders
  7. ^ OpenLaszlo 4 | OpenLaszlo
  8. ^ John Resig - Bug Fixes in JavaScript 2
  9. ^ Re: is ES4 getting too bloated?
  10. ^ IEBlog : ECMAScript 3 and Beyond
  11. ^ Albatross! : What I think about ES4
  12. ^ Brendan's Roadmap Updates: Open letter to Chris Wilson
  13. ^ Brendan's Roadmap Updates: My @media Ajax Keynote

[edit] External links