Let's look at what happens when you iterate over a map:

const myMap = Map()
  .set('one', 1)
  .set('two', 2)
  .set('three', 3);

myMap
  .forEach(i => console.log('myMap', i));
  // -> myMap 1
  // -> myMap 2
  // -> myMap 3

The iteration order is the same as the order in which you set the values. However, this iteration order isn't guaranteed. You could see a different order the next time you iterate over myMap. Let's try this with an ordered map now:

const myOrderedMap = OrderedMap()
  .set('three', 3)
  .set('two', 2)
  .set('one', 1);

myOrderedMap
  .forEach(i => console.log('myOrderedMap', i));
  // -> myOrderedMap 3
  // -> myOrderedMap 2
  // -> myOrderedMap 1

Our map, myOrderedMap, will always have the same iteration order. The order is defined as the order in which items are set. Since we're setting the value 3 first, it has an index of 0 (internally) and a key of three. If you were iterating over this map to render data in a user interface, consistent iteration order is important—the OrderedMap collections provide this guarantee.