Map objects are collections of key-value pairs where each key is unique within the collection, meaning a key can only appear once. When a Map object is iterated using a for...of loop, it returns a two-member array [key, value] for each key-value pair. Iteration follows the order in which the key-value pairs were inserted, corresponding to the sequence in which the set() method was called, provided that the key was not already present in the map at the time of insertion.
