Developers building a shopping cart must choose how to store items. An array is simple but requires looping to find or update items by ID, which becomes inefficient as carts grow. This approach works for small applications but creates performance headaches at scale.

An object offers fast key-based lookups, but keys are limited to strings. This introduces edge cases with prototype inheritance and requires careful iteration patterns. While workable, objects can be awkward for numeric product IDs and demand defensive coding practices.

The Map is purpose-built for this scenario. It supports any key type, provides clean methods like get/set/has, and handles iteration safely. For carts keyed by product ID, Map delivers cleaner code and better performance, making it the recommended choice for modern applications.