According to MDN:
A Map object can iterate its elements in insertion order – a
for..ofloop will return an array of [key, value] for each iteration.
and
Objects are similar to Maps in that both let you set keys to values, retrieve those values, delete keys, and detect whether something is stored at a key. Because of this, Objects have been used as Maps historically; however, there are important differences between Objects and Maps that make using a Map better.
An Object has a prototype, so there are default keys in the map. However, this can be bypassed using map = Object.create(null). The keys of an Object are Strings, where they can be any value for a Map. You can get the size of a Map easily while you have to manually keep track of size for an Object.
The iterability-in-order is a feature that has long been wanted by developers, in part because it ensures the same performance in all browsers. So to me that’s a big one.
The myMap.has(key) method will be especially handy, and also the myMap.size property.