Sample
Demonstrate that core-js/configurator overrides polyfill aggressiveness via usePolyfill, useNative, and useFeatureDetection, and that useNative still installs polyfills for undefined features.
sha256:e5be7751aab154725b5932787866e2f8beb21e17e99d2d2d8e5ba395c71f8f2c
PUBLISHED
L3_CONTRACT_PASS
MIT-0
Execution evidence
Declared environment and signed verification runs are separated so you can see exactly what this sample proves.
Evidence basisSigned contract pass
Verification receipts1
Verification levelL3_CONTRACT_PASS
Declared environment
- Execution context
- node
- Operating system
- linux
- Architecture
- x64
- Runtime
- node
- Language
- node
- Package manager
- npm
Verification-run environments
- Execution context
- node 22
- Operating system
- linux alpine · musl
- Architecture
- x64
- Runtime
- node 22
- Language
- javascript
- Package manager
- npm
- Execution
- container · docker
CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-18
Case
- Goal
- Demonstrate that core-js/configurator overrides polyfill aggressiveness via usePolyfill, useNative, and useFeatureDetection, and that useNative still installs polyfills for undefined features. HOW
- Packages
-
core-js 3.42.0
- Environment
- node
- Created
- 2026-08-18T00:52:08Z
Commonly assumed
Configuring core-js with useNative prevents polyfills from being installed even when the target feature is completely missing from the environment.
The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.
Contract
- Calling core-js/configurator with usePolyfill forces replacement of compliant native methods upon module import, whereas useNative preserves native implementations but still installs polyfills when the target property is undefined.
- usePolyfill with Array.prototype.toReversed replaces the native implementation.
- Normalization accepts Array#findLast and array.findlastindex interchangeably.
- useNative with structuredClone preserves the native structuredClone implementation.
- useFeatureDetection resets earlier forced aggressiveness overrides back to feature detection.
- useNative with Iterator.range installs the polyfill when the native property is absent.
- Calling configurator after a module has already been imported does not retroactively replace already-evaluated methods.
Files
- NOTES.md
- csx.json
- package-lock.json
- package.json
- test/contract.mjs
Download the source artifact (tar.gz)
Origin Seeder
csx-seed
Verification receipts
- node 22 · linux alpine/x64 · docker · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-18 · ed25519:d91480838ac982c9