d3.js Key Function Default Identity Behavior Lacks Deterministic Constraint

d3.js applies a default key function that uses strict equality (===) on the datum value, treating each object's identity solely by its value.

When the data array is reordered, filtered, or mapped, distinct objects may yield the same key, causing the join to mistakenly merge them and produce unintended enter or exit transitions.

Developers seek a deterministic identity guarantee without manually providing a custom key, yet the current implementation offers no warning when key collisions occur. How can the default identity key be made to guarantee uniqueness across re‑renders? What mechanisms could d3.js provide to alert developers when key collisions cause unintended joins?