ECMAScript 2025 JavaScript standard approved

ECMAScript 2025, the latest version of the ECMA International standard for JavaScript, has been officially approved. The specification standardizes new JavaScript capabilities including JSON modules, import attributes, new Set methods, sync iterator helpers, and regular expression modifiers.

The ECMAScript 2025 specification was finalized by ECMA International on June 25. All told, nine finished proposals on the ECMAScript development committee’s GitHub page were approved. Another proposal slated for 2025, for time duration formatting objects, appears on a different page. Development of ECMAScript is under the jurisdiction of the ECMA International Technical Committee 39 (TC39).

Note that many new JavaScript features appear in browsers even before new ECMAScript standards are approved. “One thing to note is that the vast majority of web developers are more attentive when these various features become available in their favorite browser or runtime as opposed to it being added to the JS spec, which happens afterwards,” said Ujjwal Sharma, co-chair of TC39 and co-editor of ECMA-402, the ECMAScript internationalization API specification.

For JSON modules, the proposal calls for importing JSON files as modules. This plan builds on the import attributes proposal to add the ability to import a JSON module in a common way across JavaScript environments.

For regular expressions, the regular expression escaping proposal is intended to address a situation in which developers want to build a regular expression out of a string without treating special characters from the string as special regular expression tokens, while the regular expression pattern modifiers provides the capability to control a subset of regular expression flags with a subexpression. Modifiers are especially helpful when regular expressions are defined in a context where executable code cannot be evaluated, such as a JSON configuration file of a Textmate language grammar file, the proposal states.

Also in the “regex” vein, the duplicate named capturing groups proposal allows regular expression capturing group names to be repeated. Prior to this proposal, named capturing groups in JavaScript were required to be unique.

The sync iterator helpers proposal introduces several interfaces to help with general usage and consumption of iterators in ECMAScript. Iterators are a way to represent large or possibly infinitely enumerable data sets.

Other finalized specifications for ECMAScript 2025 include:

DurationFormat objects, an ECMAScript API specification proposal. Motivating this proposal is that users need all types of time duration formatting depending on the requirements of their application.

Specifications and a reference implementation for Promise.try, which allows optimistically synchronous but safe execution of a function, and being able to work with a Promise afterward. It mirrors the async function.

Float 16 on TypedArrays, DataView, and Math.f16round, which adds float16 (aka half-precision or binary16) TypedArrays to JavaScript. This plan would add a new kind of TypedArray, Float16Array, to complement the existing Float32Array and Float64Array. It also would add two new methods on DataView for reading and setting float16 values, as getFloat16 and setFloat16, to complement the existing similar methods for working with full and double precision floats. Also featured is Math.f16round, to complement the existing Math.fround. Among the benefits of this proposal is its usefulness for GPU operations.

Import attributes, which provide syntax to import ECMAScript modules with assertions. An inline syntax for module import statements would pass on  more information alongside the module specifier. The initial application for these attributes will be to support additional types of modules across JavaScript environments, beginning with JSON modules.

Set methods for JavaScript, which add methods like union and intersection to JavaScript’s built-in Set class. Methods to be added include Set.prototype.intersection(other), Set.prototype.union(other), Set.prototype.difference(other), Set.prototype.symmetricDifference(other), Set.prototype.isSubsetOf(other), Set.prototype.isSupersetOf(other), Set.prototype.isDisjointFrom(other). These methods would require their arguments to be a Set, or at least something that looks like a Set in terms of having a numeric size property as well as keys and has methods.

The development of the ECMAScript language specification started in November 1996, based on several originating technologies including JavaScript and Microsoft’s JScript. Last year’s ECMAScript 2024 specification included features such as resizing and transferring ArrayBuffers and SharedArrayBuffers and more advanced regular expression features for working with sets of strings.