Maintaining sort order

If your application has collections that are always sorted, then you need a way to maintain that sort order. This means that once you add or change values in a collection, you have to make sure that the collection is still in the order that you expected.

Finding the insertion index

Let's say that you want to add a value to a list that's already sorted. Using push() will insert the value at the end of the list, and this isn't what you want. The insert() method can put the value at a particular index—you just have to figure out which index to use to keep the list sorted:

const sortedInsert = (item, list) => {
  let low = 0;
  let high = list.count();

  while (low < high) {
    const mid = (low + high) >>> 1;
    if (item > list.get(mid)) {
      low = mid + 1;
    } else {
      high = mid;
    }
  }
  return list.insert(low, item);
};

The sortedIndex() function takes a value and a list into which to insert the value as arguments. It then does a simple...