The algorithm React uses to diff one tree with another to determine which parts need to be changed. It is triggered before the re-rendering process starts.

To transform one tree into another, the "state of the art" algorithms have a complexity in the order of O(n³).

React implements a heuristic O(n) algorithm based on two assumptions:

• Two elements of different types will produce different trees.
• The developer can hint at which child elements may be stable across different renders with a key prop.

Conclusions:

• return element of the same type from the same component (to avoid the whole child tree destruction)
• use stable unique keys

• Reconciliation