Why Didn't My State Update Immediately? — Understanding React #6

Call setState, log the state on the very next line, and you get the old value. Call setState twice in a row and you get one increment, not two. Both of those look like bugs and neither one is. We reproduce both in React, then build mySetState ourselves — a queue and a flush, about fifteen lines — and watch the exact moment the second update overwrites the first instead of adding to it. Then the updater form, and why it's not a style preference. Full playlist:    • Understanding React   Understanding React — rebuilding React's ideas from first principles instead of memorizing the API.