Timing of effects

Although useEffect is deferred until after the browser has painted, it's guaranteed to fire before any new renders. React will always flush a previous render's effects before starting a new update.

Is this true in both concurrent and non-concurrent mode. It would appear intuitively that these two call-sites in non-concurrent mode would be deterministic:

ReactDOM.render(<Foo>, container)
ReactDOM.render(<Foo>, container)

That is it would invoke a new render before the effect in the first render has been invoked.

If so would it make more sense to specify it is only in relation to effects i.e previous effects are guaranteed to run before future effects.

As it stands, it looks appears as though the "render" call-site is non-deterministic in non-concurrent.

首先检查文档中关于 effect 会在新的 render 之前被 flush 的引述，然后将其措辞与两处 ReactDOM.render 调用点以及 concurrent 和 non-concurrent 两种行为进行比较。完成标准是文档明确说明所支持的保证，并解决该保证是普遍适用于 render，还是仅适用于 effect 的顺序。