Ensure algorithmic helpers that use data structures (e.g., deep equality, key intersections) have an explicit correctness contract and are implemented with runtime-compatible structures. - **For deep equality:** verify the algorithm enforces *all* required invariants (e.g., same keys present in both objects, not just equal lengths). Clearly decide whether special values follow native `===` semantics or “collection” semantics (e.g., treating `NaN` as equal like `Set`). - **For intersections/maps/sets:** don’t assume `Set`/custom map types are available or supported across all target runtimes. Prefer native `Map` when broadly supported, or implement a fallback/intersection that avoids `Set` when legacy environments matter. Example (avoid `Set` for key intersection): ```ts // Compatible intersection without Set function sharedKeys(a: Record, b: Record) { const out: string[] = []; for (const key in a) { if (Object.prototype.hasOwnProperty.call(b, key)) out.push(key); } return out; } ``` Apply this by (1) writing down the intended semantics (especially for equality) and (2) choosing the simplest compatible data structure/approach for the supported JavaScript environments.