Minimum common web API

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https://min-common-api.proposal.wintertc.org/
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Abstract

Minimum Common Web Platform API for Non-Browser ECMAScript-based runtimes.

Introduction

There is a wide base of ECMAScript runtime environments being used beyond web browsers, specifically in web server and edge platforms. An major benefit to this approach is the ability to use a single programming language across multiple contexts, reducing specialization and allowing for reuse of code across the server and client side.

Since code running in web browsers makes up the vast majority of ECMAScript code, runtimes are incentivised to support the same APIs as web browsers. However without a specification of which web platform APIs to be implemented, the resulting landscape provides poor interoperability across such environments.

As such, this Ecma Standard defines the Minimum common web API specification, which defines a subset of Web Platform APIs for server runtimes to implement for interoperability with the web. This is the first edition of the standard, corresponding to the 2025 snapshot. As the web platform and web server runtimes grow and evolve, the committee will aim to publish with an annual cadence.

This Ecma Standard was developed by Technical Committee 55 and was adopted by the General Assembly of December 2025.

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1. Scope

This Standard defines the 2025 snapshot of the Minimum common web API, a curated subset of APIs defined by web platform standards from W3C and WHATWG, which is intended to define a minimum set of capabilities common to browser and web server runtime environments based on ECMAScript.

The intended audience for this Standard is for web server runtime environments that want to be interoperable with the web platform. However, the set of APIs it describes may be implemented by any ECMAScript-based runtime environment that aims to be web-interoperable, even if its primary purpose is unrelated to web servers.

2. Conformance

A conforming implementation of this Standard shall provide the interfaces and properties listed in this specification, according to their definition in the corresponding W3C or WHATWG standard. A conforming implementation shall also conform to ECMA-262.

Runtime-specific extensions to any Web Platform API may be implemented by conforming runtimes. Such extensions shall be defined so that their use neither contradicts, nor causes the non-conformance of, normative functionality of any Web Platform API. Extending API surface, even without modifying existing API behaviours, should be avoided as it can reduce interoperability and portability of code across runtimes.

Runtimes may implement Web Platform APIs beyond those listed in this Standard.

Note: For example, the Performance API could be extended with additional methods or properties beyond those defined in the [HR-TIME] specifications, such as those defined in the [PERFORMANCE-TIMELINE] or [USER-TIMING] specifications.

3. Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

References

Normative References

[COMPRESSION]
Adam Rice. Compression Standard. Living Standard. URL: https://compression.spec.whatwg.org/
[CONSOLE]
Dominic Farolino; Robert Kowalski; Terin Stock. Console Standard. Living Standard. URL: https://console.spec.whatwg.org/
[DOM]
Anne van Kesteren. DOM Standard. Living Standard. URL: https://dom.spec.whatwg.org/
[ECMASCRIPT]
ECMAScript Language Specification. URL: https://tc39.es/ecma262/multipage/
[ENCODING]
Anne van Kesteren. Encoding Standard. Living Standard. URL: https://encoding.spec.whatwg.org/
[FETCH]
Anne van Kesteren. Fetch Standard. Living Standard. URL: https://fetch.spec.whatwg.org/
[FILEAPI]
Marijn Kruisselbrink. File API. URL: https://w3c.github.io/FileAPI/
[HR-TIME]
Yoav Weiss. High Resolution Time. URL: https://w3c.github.io/hr-time/
[HTML]
Anne van Kesteren; et al. HTML Standard. Living Standard. URL: https://html.spec.whatwg.org/multipage/
[RFC7231]
R. Fielding, Ed.; M. Nottingham, Ed.; J. Reschke, Ed.. HTTP Semantics. June 2022. Internet Standard. URL: https://httpwg.org/specs/rfc9110.html
[STREAMS]
Adam Rice; et al. Streams Standard. Living Standard. URL: https://streams.spec.whatwg.org/
[URL]
Anne van Kesteren. URL Standard. Living Standard. URL: https://url.spec.whatwg.org/
[URLPATTERN]
Ben Kelly; Jeremy Roman; 宍戸俊哉 (Shunya Shishido). URL Pattern Standard. Living Standard. URL: https://urlpattern.spec.whatwg.org/
[WASM-JS-API-2]
. Ms2ger. WebAssembly JavaScript Interface. URL: https://webassembly.github.io/spec/js-api/
[WASM-WEB-API-2]
. Ms2ger. WebAssembly Web API. URL: https://webassembly.github.io/spec/web-api/
[WEBCRYPTO]
Daniel Huigens. Web Cryptography Level 2. URL: https://w3c.github.io/webcrypto/
[WEBIDL]
Edgar Chen; Timothy Gu. Web IDL Standard. Living Standard. URL: https://webidl.spec.whatwg.org/
[XHR]
Anne van Kesteren. XMLHttpRequest Standard. Living Standard. URL: https://xhr.spec.whatwg.org/

Informative References

[PERFORMANCE-TIMELINE]
Nicolas Pena Moreno. Performance Timeline. URL: https://w3c.github.io/performance-timeline/
[USER-TIMING]
Nicolas Pena Moreno. User Timing Level 3. URL: https://w3c.github.io/user-timing/

4. Terms and definitions

For the purposes of this document, the terms and definitions given in ECMA-262, Compression Standard, Console Standard, DOM Standard, Encoding Standard, Fetch Standard, File API, High-Resolution Time, HTML Standard, Streams Standard, URL Standard, URL Pattern Standard, WebAssembly JavaScript Interface, WebAssembly Web API, W3C Web Cryptography Level 2, and the following apply. Externally-defined terms are mapped to source in Annex A.

4.1. Web Platform

the combination of technology standards defined by organizations such as the W3C, the WHATWG, and others as implemented by Web Browsers

4.2. Web-interoperable Runtime

ECMAScript-based runtime environment that implements this Standard

Note: Web Browsers are Web-interoperable Runtimes.
The term "Web-interoperable Runtime" is intentionally broad. The primary focus of this Standard is web server runtimes.

5. Common API Index

All Web-interoperable Runtimes conforming to this Standard shall implement each of the following Web Platform APIs. These should be implemented in accordance with their normative requirements except as specified in § 6 The Global Scope. Where any runtime environment must diverge from a normative requirement for technical or structural reasons, clear documentation shall be provided. Documentation shall include both explanation and impact of deviation.

Note: For example, since web server runtimes do not have an origin concept, they must violate [FETCH]’s requirement of appending an Origin header to network requests.

All of the following interfaces shall be exposed on the global object accessible through globalThis:

All of the following methods and properties shall be exposed on the global object accessible through globalThis, except as specified in § 6 The Global Scope:

This Standard does not require runtimes to support web workers. However, if a runtime has global scopes that map to WorkerGlobalScope (see § 6 The Global Scope), then the global object shall also expose onerror, onunhandledrejection, onrejectionhandled and self, except as specified in § 6 The Global Scope. [HTML]

6. The Global Scope

The exact type of the global scope (globalThis) can vary across runtimes. Most Web Platform APIs are defined in terms that assume Web Browser environments that specifically expose types like Window, WorkerGlobalScope, and so forth. To simplify conformance, this Standard does not require such global scope interfaces to be supported, but each global scope in a relevant runtime may be mapped to a global scope interface defined in web specifications. All interfaces, methods, and properties defined by this Standard which are required by web specifications to be exposed in a global scope interface shall be exposed on all of the runtime’s corresponding global scopes (e.g., globalThis.crypto, globalThis.ReadableStream, etc).

Note: It is expected that a runtime’s main global scope maps to Window, that web worker global scopes map to WorkerGlobalScope, etc. Global scopes that do not map to any global interface could only implement web APIs defined as [Exposed=*].

With many runtimes, adding a new global-scoped property can introduce breaking changes when the new global conflicts with existing application code. Many Web Platform APIs define global properties using the readonly attribute. [WEBIDL] To avoid introducing breaking changes, runtimes conforming to this Standard may omit the readonly attribute for properties being added to the global scope. This allows users of these runtimes to delete or overwrite these properties if they conflict with existing application code.

Whenever the global object corresponds to the Window or WorkerGlobalScope global interfaces, it should be an instance of EventTarget. Web-interoperable runtimes should follow the report an exception algorithm, and the JavaScript HostPromiseRejectionTracker host hook, as defined in [HTML]. This includes firing the error, unhandledrejection and rejectionhandled events on the global object.

In cases where it is not possible to have such global objects be an instance of EventTarget due to legacy reasons, the relevant events shall still be fired through a suitable alternative mechanism available at the global scope. This mechanism shall provide at least the same information that is provided by the relevant event interfaces if the global object were to be an EventTarget. Such runtimes shall not support the onerror, onunhandledrejection and onrejectionhandled global properties. Such runtimes are not required to implement the ErrorEvent and PromiseRejectionEvent interfaces.

Note: For example, in Node.js the global object does not implement EventTarget, and the relevant events are fired on the globalThis.process object with the names uncaughtException, unhandledRejection and rejectionHandled, respectively.

7. Requirements for default User-Agent value

The default `User-Agent` value is provided such that application code can reliably identify the runtime within which it is running. The value shall be a string conforming to the User-Agent construction in [RFC7231]:

User-Agent      = product *( RWS ( product / comment ) )
product         = token ["/" product-version]
product-version = token

The default `User-Agent` value should be treated by application code as a single, complete, opaque, unstructured value. It is recommended that the value be limited to a single product token excluding the optional product-version. The value should not include any comment components.

Note: For instance, navigator.userAgent could be set to 'MyRuntime'.

Index

Terms defined by this specification

Terms defined by reference

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