tc39.es/ecma262/

ECMAScript® 2024 Language Specification

Coming...

ECMAScript® 2023 Language Specification

ECMAScript 2023, the 14th edition, introduced 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 #! comments at the beginning of files to better facilitate executable ECMAScript files; and allowed the use of most Symbols as keys in weak collections.

ECMAScript® 2022 Language Specification

ECMAScript 2022, the 13th edition, introduced top-level await, 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 #x in obj syntax, to test for presence of private fields on objects; regular expression match indices via the /d flag, which provides start and end indices for matched substrings; the cause property on Error objects, which can be used to record a causation chain in errors; the at method for Strings, Arrays, and TypedArrays, which allows relative indexing; and Object.hasOwn, a convenient alternative to Object.prototype.hasOwnProperty.

ECMAScript® 2021 Language Specification

ECMAScript 2021, the 12th edition, introduced the replaceAll method for Strings; Promise.any, a Promise combinator that short-circuits when an input value is fulfilled; AggregateError, a new Error type to represent multiple errors at once; logical assignment operators (??=, &&=, ||=); WeakRef, for referring to a target object without preserving it from garbage collection, and FinalizationRegistry, to manage registration and unregistration of cleanup operations performed when target objects are garbage collected; separators for numeric literals (1_000); and Array.prototype.sort was made more precise, reducing the amount of cases that result in an implementation-defined sort order.

ECMAScript® 2020 Language Specification

ECMAScript 2020, the 11th edition, introduced the matchAll method for Strings, to produce an iterator for all match objects generated by a global regular expression; import(), a syntax to asynchronously import Modules with a dynamic specifier; BigInt, a new number primitive for working with arbitrary precision integers; Promise.allSettled, a new Promise combinator that does not short-circuit; globalThis, a universal way to access the global this value; dedicated export * as ns from 'module' syntax for use within modules; increased standardization of for-in enumeration order; import.meta, a host-populated object available in Modules that may contain contextual information about the Module; as well as adding two new syntax features to improve working with “nullish” values (undefined or null): nullish coalescing, a value selection operator; and optional chaining, a property access and function invocation operator that short-circuits if the value to access/invoke is nullish.

ECMAScript® 2019 Language Specification

ECMAScript 2019 introduced a few new built-in functions: flat and flatMap on Array.prototype for flattening arrays, Object.fromEntries for directly turning the return value of Object.entries into a new Object, and trimStart and trimEnd on String.prototype as better-named alternatives to the widely implemented but non-standard String.prototype.trimLeft and trimRight built-ins. In addition, it included a few minor updates to syntax and semantics. Updated syntax included optional catch binding parameters and allowing U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR) in string literals to align with JSON. Other updates included requiring that Array.prototype.sort be a stable sort, requiring that JSON.stringify return well-formed UTF-8 regardless of input, and clarifying Function.prototype.toString by requiring that it either return the corresponding original source text or a standard placeholder.

ECMAScript® 2018 Language Specification

ECMAScript 2018 introduced support for asynchronous iteration via the AsyncIterator protocol and async generators. It also included four new regular expression features: the dotAll flag, named capture groups, Unicode property escapes, and look-behind assertions. Lastly it included object rest and spread properties.

ECMAScript® 2017 Language Specification

ECMAScript 2017 introduced Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new memory model that allows multi-agent programs to communicate using atomic operations that ensure a well-defined execution order even on parallel CPUs. It also included new static methods on Object: Object.values, Object.entries, and Object.getOwnPropertyDescriptors.

ECMAScript® 2016 Language Specification

ECMAScript 2016 was the first ECMAScript edition released under Ecma TC39's new yearly release cadence and open development process. A plain-text source document was built from the ECMAScript 2015 source document to serve as the base for further development entirely on GitHub. Over the year of this standard's development, hundreds of pull requests and issues were filed representing thousands of bug fixes, editorial fixes and other improvements. Additionally, numerous software tools were developed to aid in this effort including Ecmarkup, Ecmarkdown, and Grammarkdown. ES2016 also included support for a new exponentiation operator and adds a new method to Array.prototype called includes.