Gets the number of items in the collection.
Replaces the items stored by the collection.
Items to store.
Iterate over each entry in this collection.
Function to execute for each entry.
this context used when invoking the handler function.
Adds the test item to the children. If an item with the same ID already exists, it'll be replaced.
Item to add.
Removes a single test item from the collection.
Item ID to delete.
Efficiently gets a test item by ID, if it exists, in the children.
Item ID to get.
The found item or undefined if it does not exist.