Understanding Concurrency in React

A user typed three letters into the search box below, 30 milliseconds apart. The third key was pressed at 60 ms, but React did not handle it until 440 ms, and the final list appeared at 489 ms. For most of that time the input looked frozen, because the browser could not repaint it while React was busy rendering a long list.

This chapter is about the feature that removes that freeze. Before looking at the hooks, it helps to see exactly why the freeze happens and what React does differently when it renders concurrently.