Maps don't preserve order the way that lists do. When you push a value to a list, the value will always be in the same position because lists are indexed. With maps, the order of a particular value doesn't matter because you can look it up by its key. When you're iterating over maps, ordering can become a problem though.
The ordering of list values is guaranteed because lists are an indexed collection. Maps are a keyed collection, which means that the order in which key-value pairs are added isn't guaranteed to be preserved. For example, let's say that I call myMap.set('one', 1).set('two', 2)
. If you were to iterate over this map, one
would probably come before two
. But this is misleading, because there are no ordering guarantees when it comes to iterating over maps. This could be a problem if your application expects iteration ordering to be consistent.