React Concurrent Mode
This is a wonderful example of a well engineered solution to the wrong problem.  React is a wonderful view library, and if limited to that use it is remarkably fast and easy to use.But the usual way of building things is to treat React as a total web app framework.  The terminology is very confused: they still call it "rendering", even though it now usually includes data fetching, complex manipulations, event processing, etc.  You just `React.render` once when your page first loads and then child components take care of the rest.  It should really be called `React.start`.> The reason for the stutter is simple: once rendering begins, it can’t be interrupted.Rendering should never need to be interrupted.  If your app is architected to have any rendering operation take long enough that it's perceptible to the user, STOP DOING THAT THING DURING RENDERING.Want a performant web app?  Apply separation of concerns properly, and limit your use of React to the view layer.