ECMAScript is a JavaScript standard developed by Ecma International. Since 2015, major versions have been published every June.
ECMAScript 2025, the 16th and current version, was released in June 2025.
Versions
Edition Date published Name Changes from prior edition Editor 1 June 1997 First edition based on JavaScript 1.1 as implemented in Netscape Navigator 3.0. Guy L. Steele Jr. 2 June 1998 Editorial changes to keep the specification fully aligned with ISO/IEC 16262:1998. Mike Cowlishaw 3 December 1999 Based on JavaScript 1.2 as implemented in Netscape Navigator 4.0. 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 4 Abandoned (last draft 30 June 2003) ECMAScript 4 (ES4) The 4th edition was abandoned due to political differences concerning language complexity. Many features proposed for the 4th edition have been completely dropped; some were incorporated into the sixth edition. 5 December 2009ECMAScript 5 (ES5) 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 accommodates behavior 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.Archived at Ghostarchive and the Wayback Machine: Pratap Lakshman, Allen Wirfs-Brock 5.1 June 2011 Changes to keep the specification fully aligned with ISO/IEC 16262:2011. Pratap Lakshman, Allen Wirfs-Brock 6 June 2015ECMAScript 2015 (ES2015) See #6th edition – ECMAScript 2015 Allen Wirfs-Brock 7 June 2016ECMAScript 2016 (ES2016) See #7th edition – ECMAScript 2016 Brian Terlson 8 June 2017ECMAScript 2017 (ES2017) See #8th edition – ECMAScript 2017 Brian Terlson 9 June 2018ECMAScript 2018 (ES2018) See #9th edition – ECMAScript 2018 Brian Terlson 10 June 2019ECMAScript 2019 (ES2019) See #10th edition – ECMAScript 2019 Brian Terlson, Bradley Farias, Jordan Harband 11 June 2020ECMAScript 2020 (ES2020) See #11th edition – ECMAScript 2020 Jordan Harband, Kevin Smith 12 June 2021ECMAScript 2021 (ES2021) See #12th edition – ECMAScript 2021 Jordan Harband, Shu-yu Guo, Michael Ficarra, Kevin Gibbons 13 June 2022ECMAScript 2022 (ES2022) See #13th edition – ECMAScript 2022 Shu-yu Guo, Michael Ficarra, Kevin Gibbons14June 2023ECMAScript 2023 (ES2023)See #14th edition – ECMAScript 2023Shu-yu Guo, Michael Ficarra, Kevin Gibbons15June 2024ECMAScript 2024 (ES2024)See #15th edition – ECMAScript 2024Shu-yu Guo, Michael Ficarra, Kevin Gibbons16June 2025ECMAScript 2025 (ES2025)See #16th edition – ECMAScript 2025Shu-yu Guo, Michael Ficarra, Kevin Gibbons17June 2026ECMAScript 2026 (ES2026)See #17th edition – ECMAScript 2026Shu-yu Guo, Michael Ficarra, Kevin Gibbons18(pending)ECMAScript 2027 (ES2027)Pending, see features being considered: #ES.Next(pending)
In June 2004, Ecma International published ECMA-357 standard, defining an extension to ECMAScript, known as ECMAScript for XML (E4X). Ecma also defined a "Compact Profile" for ECMAScript – known as ES-CP, or ECMA 327 – that was designed for resource-constrained devices, which was withdrawn in 2015.2015-03-24 Meeting Notes . ESDiscuss. Also see Ecma withdrawn Standards . ECMA.
4th edition (abandoned) The proposed 4th edition of ECMA-262 (ECMAScript 4 or ES4) would have been the first major update to ECMAScript since the 3rd edition was published in 1999. The specification (along with a reference implementation) was originally targeted for completion by October 2008. The first draft was dated February 1999. An overview of the language was released by the working group on 23 October 2007.
By August 2008, the ECMAScript 4th edition proposal had been scaled back into a project code named ECMAScript Harmony. Features under discussion for Harmony at the time included: classes, a module system, optional type annotations and static typing, probably using a structural type system, generators and iterators, destructuring assignment, and algebraic data types.
The intent of these features was partly to better support programming in the large, and to allow sacrificing some of the script's ability to be dynamic to improve performance. For example, Tamarin – the virtual machine for ActionScript, developed and open-sourced by Adobe – has just-in-time compilation (JIT) support for certain classes of scripts.
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 been folded into the ECMAScript, 5th Edition specification.
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 ECMAScript for XML (E4X) standard. The update has not been without controversy. In late 2007, a debate between Eich, later 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 challenged critics to give specific examples of incompatibility. He 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 4 introduces a strict typing system. For example, a function add() could look like the following:
function add(a: int, b: int): int { return a + b; }
The following primitive types were defined:
Variables could have the following modifiers: static: makes a variable a class variable prototype: adds a variable to the class prototype object, with a get/set accessor
Classes were given the following modifiers: dynamic: allows properties to be added to instances at runtime final: cannot be extended by other classes internal: visible only to references in the current package public: visible to references globally
Class constructors were declared with the function keyword (rather than constructor), and took the name of the class itself:
class X { private var value: int;
public function X(i: int) { value = i;
Getter and setter methods were also defined with the get and set keywords: class X { private var _value: int;
function get value(): int { return _value;
function set value(n: int): void { _value = n;
var x: X = new X(); x.value = 10;
Functions could have the following modifiers: static: makes the function a trait of the class, rather than an instance (i.e. a static method) final: declares a function cannot be overriden override: overrides a method of the same name and signature native: declares a function to be "implementation-defined"
Interfaces were introduced, which, much like Java interfaces, define a contract between an instance and code that consumes it.
interface Greetings { function hello(): void; function goodMorning(): void; }
class Greeter implements Greetings { public function hello(): void { print("Hello, world!");
public function goodMorning(): void { print("Good morning, world!");
var greeter: Greetings = new Greeter(); greeter.hello();
ECMAScript 4 additionally introduced packages, which acted like packages in Java or namespaces in C++ and C#. In addition, an "unnamed package" basically acted as the global namespace, which was implicitly imported by all other packages (and given by package { /* ... */ }).
package org.wikipedia { public class Article extends WikiObject { // ...
import org.wikipedia.*; // Adds all symbols from org.wikipedia into scope import org.wiktionary.Language; // Adds type "org.wiktionary.Language" into scope
In this example, Article has a fully-qualified name of org.wikipedia.Article. While modern ECMAScript features modules, ECMAScript 4 packages behaved more like a global naming scheme, akin to those of Java.
Namespaces also existed as a separate feature from packages, and acted as a qualifier of the definition's name.
package org.wikipedia.examples { public namespace English; public namespace French;
public class BilingualGreeter { English function hello(): void { console.log("Hello, world!");
French function hello(): void { console.log("Bonjour, le monde!");
import org.wikipedia.examples.BilingualGreeter;
var greeter: BilingualGreeter = new BilingualGreeter(); use namespace English; // add all English namespace identifiers into scope
greeter.hello(); // invokes English version greeter.French::hello(); // invokes French version
5th edition – ECMAScript 2009 Yahoo, Microsoft, Google, 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 in July 2008: Brendan Eich announced that Ecma TC39 would focus work on the ECMAScript 3.1 (later renamed to ECMAScript, 5th Edition) project with full collaboration of all parties, and vendors would target at least two interoperable implementations by early 2009. In April 2009, Ecma TC39 published the "final" draft of the 5th edition and announced that testing of interoperable implementations was expected to be completed by mid-July. On 3 December 2009, ECMA-262 5th edition was published.
Additions include JSON, String.trim() to easily remove whitespaces surrounding a string (" example " to "example"), String.charAt() to return a single character from a given position in a string, and Array.isArray(). A comma after the final pair of values in an object (var example = { "property1":"value1", "property2":"value2", }) also no longer causes a syntax error.JavaScript Versions from W3schools
6th edition – ECMAScript 2015