When is setState in React synchronous and when is it asynchronous?

1. A:

In React, if an event handler is raised by React (such as an event handler raised by onClick), calls to setState do not update this.state synchronously. “In addition” refers to the event handlers added directly via addEventListener, bypassreact, and the asynchronous calls made via setTimeout/setInterval.

2. Note:

When I say synchronous asynchrony, IT’s not really synchronous asynchrony, it’s done synchronously.

By asynchrony, I mean that multiple states are composited together for batch updates.