Stage 3 Update: Accessible Object.prototype.hasOwnProperty

Jamie Kyle (Rome) & Tierney Cyren (Microsoft)

Super fast explainer

• Object.prototype.hasOwnProperty() is not always reliably accessible due to things like Object.create(null)
• Code like Object.prototype.hasOwnProperty.call(obj, prop) is common, but also requires understanding a lot of concepts all at once for new users
• There are lots of libraries like “has” and “lodash.has” that make hasOwnProperty() easier to use (with billions of npm downloads!)
• Object.hasOwn(obj, key) mirrors hasOwnProperty.call(obj, key) to make it more accessible
• Besides a flip in the ordering of their ToObject and ToPropertyKey steps (fixing a legacy issue), they are identical and can share implementations.

Status: Ecma262 Spec

• Prepared & Editor-Approved ecma262 PR: tc39/ecma262#2415

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✅

Status: Test262 Tests

• Merged: tc39/test262#2995

✅

Status: Implementations

🚀 V8: Implemented, only available with --harmony-object-has-own

🚀 SpiderMonkey: Implemented, only available in nightly builds

🛠️ JavaScriptCore: In Progress? rdar://problem/78782545 ??

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Others:

🚀 Serenity LibJS: SerenityOS/serenity@3ee092

🚀 engine262: engine262/engine262#163

👍

Status: Community Polyfills

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🚀 npm: object.hasown

🚀 CoreJS

🚀 Babel

Status: Community Codemod

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gist.github.com/jamiebuilds/f4ff76397d31b69c484240379170af8c

Status: Community Feedback

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Feedback tracking issue: tc39/proposal-accessible-object-hasownproperty#18

• We’ve mostly heard excitement for this feature on social media
• We’ve heard from a couple users that they’ve started using polyfills in their codebases successfully
• Thousands of core-js/es-shims users have merged PRs including the Object.hasOwn() polyfill https://github.com/search?q=Object.hasOwn+is%3Apr+is%3Amerged&type=Issues

👍

Status: Stage 4 Requirements Overview

Tracking issue: tc39/proposal-accessible-object-hasownproperty#6

✅ Ecma262 PR is editor-approved and ready to be merged

✅ Test262 tests merged

👍 Implemented (feature flagged) in two browsers

👍 Getting more community feedback with polyfills (how much do we need?)

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Plan to seek Stage 4 pending feedback from browsers

Thanks

Champion: Tierney Cyren

Spec Text Reviewers: Jordan Harband, Kevin Gibbons, Nicolo Ribaudo

Implementers/Reviewers:

• V8: Victor Gomes, Shu-yu Guo, Jakob Gruber
• SpiderMonkey: Yulia Startsev, Matthew Gaudet
• engine262: Gus Caplan
• Polyfills: Jordan Harband, Denis Pushkarev, Nicolo Ribaudo

Test262 Reviewers: Mike Pennisi, Rick Waldron, Nicolo Ribaudo

Proposal Feedback: Mathias Bynens, Denis Pushkarev, Jordan Harband, Justin Ridgewell, Jason Yu, HE Shi-Jun, Kevin Gibbons, and others!

Questions?