core-js Array.prototype.flat performance variance in legacy engines

Polyfill Specification Compliance

The core-js library implements Array.prototype.flat to ensure compatibility with the ECMAScript specification across legacy environments. While the library provides modular imports to minimize bundle size, the internal implementation must balance strict spec compliance with execution efficiency.

Execution Trade-offs

In certain legacy engines, there is a known tension between a fully compliant flattening algorithm and optimized shortcuts that may bypass specific edge-case behaviors of the specification to improve performance. This becomes critical when processing deeply nested arrays where recursive overhead is significant.

• Targeting legacy environments via @babel/preset-env.
• Requirement for spec-compliant depth handling.
• Potential performance degradation in non-native environments.

Does core-js prioritize absolute specification adherence over execution speed for Array.prototype.flat in legacy engines, and is there a configuration to toggle between a compliant and a performance-optimized implementation?