The simplest way to empty a collection is to replace it with a new instance, as shown here:

const empty = (collection) => {
  if (collection instanceof List) {
    return List();
  }
  if (collection instanceof Map) {
    return Map();
  }
  return null;
};

const myList = List.of(1, 2);
const myMap = Map.of('one', 1, 'two', 2);

const myEmptyList = empty(myList);
const myEmptyMap = empty(myMap);

console.log('myList', myList.toJS());
// -> myList [ 1, 2 ]
console.log('myEmptyList', myEmptyList.toJS());
// -> myEmptyList []
console.log('myMap', myMap.toJS());
// -> myMap { one: 1, two: 2 }
console.log('myEmptyMap', myEmptyMap.toJS());
// -> myEmptyMap {}

We've created a little helper function called empty(). The idea is that it accepts either a list or map as its argument. Depending on the type of collection, a new instance is returned. Then, we can assign this new value to myEmptyList. Remember, as long as myList is referenced, it will never be garbage-collected. If you don't want this to happen, you could store the collection in a variable instead of in a constant. Then, empty() can simply replace the old collection:

var myList = List.of(1, 2);
myList = empty(myList);

Now, the garbage collector can pick up the first collection with the values 1 and 2.