Sample
Demonstrate how @babel/preset-env applies targeted engine bugfix transforms such as Safari identifier destructuring collision avoidance and RegExp modifier polyfills without downleveling modern ES syntax
sha256:55b7a376efcdee05a18f670f71e3a6c5a665fd5258f9260c49a8e20b7656eccd
PUBLISHED
L3_CONTRACT_PASS
MIT-0
Case
- Goal
- Demonstrate how @babel/preset-env applies targeted engine bugfix transforms such as Safari identifier destructuring collision avoidance and RegExp modifier polyfills without downleveling modern ES syntax HOW
- Packages
- @babel/core 8.0.1 @babel/preset-env 8.0.2
- Environment
- node
- Created
- 2026-08-16T15:50:12Z
Commonly assumed
Targeting an environment with known JavaScript engine bugs forces preset-env to downlevel the surrounding modern ES2015+ syntax categories down to ES5 helper functions.
The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.
Contract
- preset-env targeting Safari 14 preserves native ES2015 destructuring syntax and parameter defaults while surgically renaming only the colliding parameter identifier to avoid JavaScriptCore scope shadowing bugs
- preset-env targeting Safari 16.4 leaves matching parameter names untouched because the JavaScriptCore destructuring scope collision was resolved upstream
- preset-env targeting IE 11 fully downlevels destructuring parameters to temp variable property accesses
- preset-env compiles inline RegExp modifiers into case-expanded character classes for Node 18 targets lacking native modifier support
- preset-env with explicit resource management transpiles using declarations with disposable stack context helpers for pre-explicit-resource-management targets
Files
- NOTES.md
- csx.json
- package-lock.json
- package.json
- test/contract.mjs
Download the verified artifact (tar.gz) — the exact bytes the contract ran against
Origin Seeder
Verification receipts
- node 22 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-16 · ed25519:d91480838ac982c9