Add polyfills for new Set methods (union, intersection, difference, symmetricDifference, isSubsetOf, isSupersetOf, isDisjointFrom)

[Copilot]

Safari 16.4 lacks support for the seven newly-baseline Set methods available in ES2024/TypeScript's es2024 lib. This adds polyfills so they can be used safely today.

Changes

• src/set-methods.ts — New polyfill module implementing all seven methods against a SetLike<T> interface (has, keys, size) per TC39 spec, including spec-aligned optimizations (e.g. isSubsetOf short-circuits when this.size > other.size; isDisjointFrom iterates the smaller set). Follows the standard isSupported() / isPolyfilled() / apply() pattern.
• src/index.ts — Registers setMethods alongside existing polyfills.
• test/set-methods.js — Tests for all seven methods covering common cases and edge cases (empty sets, disjoint sets, identical sets).

Usage

import { apply } from '@github/browser-support/set-methods'
apply() // no-op if natively supported

const a = new Set([1, 2, 3])
const b = new Set([2, 3, 4])

a.union(b)               // Set {1, 2, 3, 4}
a.intersection(b)        // Set {2, 3}
a.difference(b)          // Set {1}
a.symmetricDifference(b) // Set {1, 4}
a.isSubsetOf(b)          // false
a.isSupersetOf(b)        // false
a.isDisjointFrom(b)      // false

Warning

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• accounts.google.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4006 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-z0xwaJ --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,16526546639982034433,11159440813740539228,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome-stable --allow-pre-commit-input --disable-REDACTED-networking --disable-REDACTED-timer-throttling --disable-REDACTEDing-occluded-windows --disable-breakpad --disable-client-side-phishing-detection --disable-component-extensions-with-REDACTED-pages --disable-crash-reporter --disable-default-apps --disable-dev-shm-usage --disable-extensions --disable-hang-monitor --disable-infobars --disable-ipc-flooding-protection --disable-popup-blocking --disable-prompt-on-repost --disable-renderer-REDACTEDing --disable-search-engine-choice-screen --disable-sync (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4258 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-IkdZcd --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,4382833278840495840,8209209942178505960,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• api.openweathermap.org
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/.npm/_npx/60193c364be7f30b/node_modules/.bin/wtr test/set-methods.js --node-resolve (dns block)
• clients2.google.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4006 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-z0xwaJ --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,16526546639982034433,11159440813740539228,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome-stable --allow-pre-commit-input --disable-REDACTED-networking --disable-REDACTED-timer-throttling --disable-REDACTEDing-occluded-windows --disable-breakpad --disable-client-side-phishing-detection --disable-component-extensions-with-REDACTED-pages --disable-crash-reporter --disable-default-apps --disable-dev-shm-usage --disable-extensions --disable-hang-monitor --disable-infobars --disable-ipc-flooding-protection --disable-popup-blocking --disable-prompt-on-repost --disable-renderer-REDACTEDing --disable-search-engine-choice-screen --disable-sync (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4258 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-IkdZcd --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,4382833278840495840,8209209942178505960,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• safebrowsingohttpgateway.googleapis.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4006 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-z0xwaJ --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,16526546639982034433,11159440813740539228,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome-stable --allow-pre-commit-input --disable-REDACTED-networking --disable-REDACTED-timer-throttling --disable-REDACTEDing-occluded-windows --disable-breakpad --disable-client-side-phishing-detection --disable-component-extensions-with-REDACTED-pages --disable-crash-reporter --disable-default-apps --disable-dev-shm-usage --disable-extensions --disable-hang-monitor --disable-infobars --disable-ipc-flooding-protection --disable-popup-blocking --disable-prompt-on-repost --disable-renderer-REDACTEDing --disable-search-engine-choice-screen --disable-sync (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4258 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-IkdZcd --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,4382833278840495840,8209209942178505960,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
• www.google.com
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4006 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-z0xwaJ --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,16526546639982034433,11159440813740539228,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)
  • Triggering command: /opt/google/chrome/chrome /usr/bin/google-chrome-stable --allow-pre-commit-input --disable-REDACTED-networking --disable-REDACTED-timer-throttling --disable-REDACTEDing-occluded-windows --disable-breakpad --disable-client-side-phishing-detection --disable-component-extensions-with-REDACTED-pages --disable-crash-reporter --disable-default-apps --disable-dev-shm-usage --disable-extensions --disable-hang-monitor --disable-infobars --disable-ipc-flooding-protection --disable-popup-blocking --disable-prompt-on-repost --disable-renderer-REDACTEDing --disable-search-engine-choice-screen --disable-sync (dns block)
  • Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --disable-dev-shm-usage --use-angle=swiftshader-webgl --mute-audio --crashpad-handler-pid=4258 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/puppeteer_dev_chrome_profile-IkdZcd --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,4382833278840495840,8209209942178505960,262144 --enable-features=PdfOopif --disable-features=AcceptCHFrame,IsolateSandboxedIframes,MediaRouter,OptimizationHints,PaintHolding,ProcessPerSiteUpToMainFrameThreshold,Translate --variations-seed-version --trace-process-track-uuid=3190708989122997041 (dns block)

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add polyfill for newly available Set methods</issue_title>
<issue_description>when using typescript es2024 Set method types are available, but Safari 16.4 still doesn't support them (they're baselines newly available). we shouldpolyfill and remove once they fall off support

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/intersection
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/difference
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/isDisjointFrom
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/isSubsetOf
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/isSupersetOf
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/symmetricDifference
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/union

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add polyfill for newly available Set methods #109

---

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[Copilot]

Pull request overview

Adds an ES2024 Set-methods polyfill module so consumers can safely use the newly-baseline Set APIs (e.g. union, intersection) in browsers like Safari 16.4 that lack native support, and registers it in the library’s aggregated polyfill entrypoint.

Changes:

• Added src/set-methods.ts implementing union, intersection, difference, symmetricDifference, isSubsetOf, isSupersetOf, isDisjointFrom plus isSupported() / isPolyfilled() / apply().
• Registered the new polyfill under polyfills in src/index.ts.
• Added test/set-methods.js with unit tests for the exported implementations.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/set-methods.ts	New polyfill module implementing and installing the ES2024 Set methods.
src/index.ts	Registers setMethods in the global polyfills list.
test/set-methods.js	Adds tests for the new Set-method implementations.

Comments suppressed due to low confidence (3)

src/set-methods.ts:101

• isSupported() only checks property existence via 'name' in Set.prototype, which can return true even if a non-function value is present (or something is inherited). This can cause apply() to be skipped while the methods still aren't callable. Consider also checking typeof Set.prototype.union === 'function' (and the rest) like the other polyfills do.

export function isSupported(): boolean {
  return (
    'union' in Set.prototype &&
    'intersection' in Set.prototype &&
    'difference' in Set.prototype &&
    'symmetricDifference' in Set.prototype &&
    'isSubsetOf' in Set.prototype &&
    'isSupersetOf' in Set.prototype &&
    'isDisjointFrom' in Set.prototype
  )

src/set-methods.ts:129

• apply() installs all 7 methods whenever any of them are missing. In environments with partial native support, this will overwrite the native implementations (and potentially change behavior/perf). Prefer installing each method only if it's missing (similar to iterator-helpers.ts), so native methods are preserved.

export function apply(): void {
  if (!isSupported()) {
    Object.assign(Set.prototype, {
      union,
      intersection,
      difference,
      symmetricDifference,
      isSubsetOf,
      isSupersetOf,
      isDisjointFrom,
    })

test/set-methods.js:23

• Tests currently exercise the exported functions via .call(...) but don't verify apply() actually installs the methods on Set.prototype (e.g., new Set([1]).union(...)) or that isPolyfilled() becomes true after applying. Adding at least one prototype-level test would cover the primary integration path.

  it('has standard isSupported, isPolyfilled, apply API', () => {
    expect(isSupported).to.be.a('function')
    expect(isPolyfilled).to.be.a('function')
    expect(apply).to.be.a('function')
    expect(isSupported()).to.be.a('boolean')
    expect(isPolyfilled()).to.equal(false)
  })

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[jibrang]

We are not adding this check: proto['union'] === union && to isSupported. Is that intended?

[mattcosta7]

yep, I believe that's right, if I understand it correctly?

isSupported supports both polyfilled and not, so it should cover both cases (once the polyfill is applied), while isPolyfilled validates whether the support came from the polyfill applied or by built in support (which I think for us is everything but safari 16 or 17)

[jibrang]

Oh I see, yeah that makes sense!