copyWithin(): moving values inside the array

Useful to know

copyWithin() copies part of an array onto another part of it. For example, [1, 2, 3, 4].copyWithin(0, 2) gives [3, 4, 3, 4]. The length remains four . [1]

This is different from adding more elements. Existing target positions are overwritten. Before use, write down which indexes are the source and which are the target, especially when overlapping. If you need independent retrieval without change, use a copy method. The name suggests the scope: the operation remains inside the same container.