ECMAScript is a JavaScript standard developed by Ecma International. Since 2015, major versions have been published every June.
ECMAScript 2024, the 14th and current version, was released in June 2024.
| 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.[1] | 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.[2] 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) | Fourth Edition was abandoned, due to political differences concerning language complexity. Many features proposed for the Fourth Edition have been completely dropped; some were incorporated into the sixth edition. | ||
| 5 | December 2009 | 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.[3] | 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 2015 | ECMAScript 2015 (ES2015) | See
| Allen Wirfs-Brock | |
| 7 | June 2016 | ECMAScript 2016 (ES2016) | See
| Brian Terlson | |
| 8 | June 2017 | ECMAScript 2017 (ES2017) | See
| Brian Terlson | |
| 9 | June 2018 | ECMAScript 2018 (ES2018) | See
| Brian Terlson | |
| 10 | June 2019 | ECMAScript 2019 (ES2019) | See
| Brian Terlson, Bradley Farias, Jordan Harband | |
| 11 | June 2020 | ECMAScript 2020 (ES2020) | See
| Jordan Harband, Kevin Smith | |
| 12 | June 2021[4] | ECMAScript 2021 (ES2021) | See
| Jordan Harband, Shu-yu Guo, Michael Ficarra, Kevin Gibbons | |
| 13 | June 2022[5] | ECMAScript 2022 (ES2022) | See
| Shu-yu Guo, Michael Ficarra, Kevin Gibbons | |
| 14 | June 2023[6] | ECMAScript 2023 (ES2023) | See
| Shu-yu Guo, Michael Ficarra, Kevin Gibbons | |
| 15 | June 2024[7] | ECMAScript 2024 (ES2024) | See
| Shu-yu Guo, Michael Ficarra, Kevin Gibbons | |
| 16 | (pending) | ECMAScript 2025 (ES2025) | Pending, see features being considered:
| (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.[8]
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.[9] The first draft was dated February 1999.[10] An overview of the language was released by the working group on 23 October 2007.[11]
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:
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.[12] [13] These fixes and others, and support for JSON encoding/decoding, have been folded into the ECMAScript, 5th Edition specification.[14]
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",[15] and that stakeholders who opposed the changes were being "hidden from view".[16] 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.[17] 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.[18]
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.[19] [20] 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.[21] On December 3, 2009, ECMA-262 5th edition was published.[22]
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.[23]
The 6th edition, ECMAScript 6 (ES6) and later renamed to ECMAScript 2015, was finalized in June 2015.[24] [25] This update adds significant new syntax for writing complex applications, including class declarations (let keyword for local declarations, const keyword for constant local declarations, binary data, typed arrays, new collections (maps, sets and WeakMap), promises, number and math enhancements, reflection, proxies (metaprogramming for virtual objects and wrappers) and template literals using backticks (`) for multi-line strings without escape characters.[26] [27] The complete list is extensive.[28] [29] As the first "ECMAScript Harmony" specification, it is also known as "ES6 Harmony".
The 7th edition, or ECMAScript 2016, was finalized in June 2016.[30] Its features include exponentiation operator ** for numbers, await, async keywords for asynchronous programming (as a preparation for ES2017), and the function.[30] The exponentiation operator is equivalent to, but provides a simpler syntax similar to languages like Python, F#, Perl, and Ruby. async / await was hailed as an easier way to use promises and develop asynchronous code.
The 8th edition, or ECMAScript 2017, was finalized in June 2017.[31] Its features include the, and functions for easy manipulation of Objects, async / await constructions that use generators and promises, and additional features for concurrency and atomics. It also includes String.prototype.padStart.[32]
The 9th edition, or ECMAScript 2018, was finalized in June 2018.[33] New features include the spread operator and rest parameters (...) for object literals, asynchronous iteration, Promise.prototype.finally and additions to RegExp.[33]
The spread operator allows for the easy copying of object properties, as shown below.
let objectClone = Object.assign(object) // before ES2018let objectClone = // ES2018 syntax
let otherObject = console.log(otherObject) // ->
The 10th edition, or ECMAScript 2019, was published in June 2019.[34] Added features include, but are not limited to, Array.prototype.flat, Array.prototype.flatMap, changes to Array.sort, and Object.fromEntries.
is now guaranteed to be stable, meaning that elements with equal sorting keys will not change relative order before and after the sort operation. Array.prototype.flat(depth=1) flattens an array to a specified depth, meaning that all subarray elements (up to the specified depth) are concatenated recursively.
Another notable change is that so-called catch binding became optional.[35]
The 11th edition, or ECMAScript 2020, was published in June 2020.[36] In addition to new functions, this version introduces a BigInt primitive type for arbitrary-sized integers, the nullish coalescing operator, and the globalThis object.
BigInts are created either with the constructor or with the syntax, where "n" is placed after the number literal. BigInts allow the representation and manipulation of integers beyond, while Numbers are represented by a double-precision 64-bit IEEE 754 value. The built-in functions in are not compatible with BigInts; for example, exponentiation of BigInts must be done with the operator instead of .
The nullish coalescing operator,, returns its right-hand side operand when its left-hand side is or . This contrasts with the operator, which would return for all "falsy" values, such as the ones below.
Optional chaining makes it possible to access the nested properties of an object without having an AND check at each level. An example is . If any of the properties are not present, will be .
The 12th edition, ECMAScript 2021, was published in June 2021. This version introduces the method for strings;, a promise combinator that short-circuits when an input value is fulfilled;, a new error type to represent multiple errors at once; logical assignment operators (||=);, for referring to a target object without preserving it from garbage collection, and, to manage registration and unregistration of cleanup operations performed when target objects are garbage collected; separators for numeric literals ; and was made more precise, reducing the number of cases that result in an implementation-defined sort order.
The 13th edition, ECMAScript 2022, was published in June 2022. This version introduces top-level, allowing the keyword to be used at the top level of modules; new class elements: public and private instance fields, public and private static fields, private instance methods and accessors, and private static methods and accessors; static blocks inside classes, to perform per-class evaluation initialization; the syntax, to test for presence of private fields on objects; regular expression match indices via the flag, which provides start and end indices for matched substrings; the property on objects, which can be used to record a causation chain in errors; the method for Strings, Arrays, and TypedArrays, which allows relative indexing; and, a convenient alternative to .
The 14th edition, ECMAScript 2023, was published in June 2023.[37] This version introduces the toSorted, toReversed, with, findLast, and findLastIndex methods on Array.prototype and TypedArray.prototype, as well as the toSpliced method on Array.prototype; added support for #! shebang comments at the beginning of files to better facilitate executable ECMAScript files; and allowed the use of most Symbols as keys in weak collections.
The 15th edition, ECMAScript 2024, was published in June 2024.[38] This version introduces the Object.groupBy and Map.groupBy static methods, Promise.withResolvers, and the /v unicode flag for regular expressions.
The Object.groupBy and Map.groupBy methods groups an iterable using the return value of a provided callback function.
const obj = Object.groupBy(arr, (el) => el.year);// console.log(obj);
Promise.withResolvers provides a simple way to get a promise's resolve and reject functions directly without having to assign them in the constructor.[39]
// ES 2024const = Promise.withResolvers;The /v flag in regular expressions is simply an improved version of the /u flag, but as it makes backwards-incompatible changes it had to be introduced as a new flag.[40]
ES.Next is a dynamic name that refers to whatever the next version is at the time of writing. ES.Next features include finished proposals (aka "stage 4 proposals") as listed at finished proposals that are not part of a ratified specification. The language committee follows a "living spec" model, so these changes are part of the standard, and ratification is a formality. [41]