Launching Test262 Results on MDN Web Docs

We are excited to announce support for report embedding on test262.report, along with a new MDN collaboration to bring up-to-date information about ECMAScript feature conformance to MDN Web Docs. Starting today, you can view test results from Test262 Report, updated daily and embedded directly on MDN pages for the newest ECMAScript features where interoperability and conformance are improving day to day, such as globalThis. This launch marks the start of an experiment with MDN Web Docs to find new ways to bring relevant information from our work with JavaScript conformance testing to a broader set of web developers.

MDN Web Docs documents HTML, CSS, and ECMAScript features along with inline code snippets, helpful examples, and browser compatibility information. Many web developers use MDN Web Docs as an easy-to-browse and accessible alternative to the various W3C, WHATWG and ECMAScript specifications. MDN Web Docs pages, including sections on compatibility information, are maintained on GitHub where contributors can open a pull request to make suggestions or mark a change in browser compatibility status. With a few exceptions, compatibility information for a given feature and browser pair is usually manually evaluated by MDN maintainers, and marked as “full support,” “no support,” or “compatibility unknown.”

Over the past year at Bocoup, we have developed and are maintaining Test262 Report to provide JavaScript developers with a simple, intuitive interface to browse information about the state of new and existing language features across implementations. Test262 Report is based on daily runs of Test262, the ECMA-262 (aka ECMAScript) test suite, in nightly builds (or latest releases) of JavaScript engines, including ChakraCore, JavaScriptCore, SpiderMonkey, V8, and (as of recently) Moddable XS. For example, on the BigInt results page, you can view specific language syntax or Internationalization API tests, track support across engines, find the link to the original TC39 proposal, and at the time of this writing see over six months of historical test results (back to when we started storing historical runs). This data complements the current compatibility information on MDN Web Docs by providing granular test data for specific functionality, updates against nightly versions of the engines, and progress towards 100% conformance—fully compatible implementations across the JavaScript ecosystem.

The MDN Test262 Report embed is currently implemented by rendering an iframe from test262.report/embed/ into the MDN page for the newest ECMAScript features, including:

• Optional chaining
• globalThis
• BigInt
• import.meta
• Hashbang Comments
• import
• Promise.allSettled()

This MDN feature will be treated as an experiment with the goal of testing whether MDN readers find the additional information helpful.

We plan to continue working on the embed itself based on feedback from MDN readers. If you find the Test262 information helpful in the context of new ECMAScript feature documentation, please click the “Yes” button next to “Is this helpful?” under the embedded table. We’d also love to hear more detailed feedback on the Test262 Report issue tracker on GitHub. We look forward to continuing our collaboration with the MDN Web Docs team and designing new ways to help JavaScript developers find the most up-to-date information about feature interoperability!

Embed Your Own Report

These embeddable iframes can also be built and accessed from Test262 Report, by clicking the Embed button in the top right of the results chart. The embed code will include a link to a report view for the level of detail and date of the page you are on when you click it, or to an evergreen report based on the latest data, if you so choose.

We’d also like to invite the ECMAScript, Node.js, Web Developer and Engine Implementer communities to embed these reports in your future analyses of web platform feature interoperability!