> setState mutates some “global” state Is this true? Maybe I'm reading it wrong but this.setState in a React.Component just transparently calls out to `this.up

> setState mutates some “global” state Is this true? Maybe I'm reading it wrong but this.setState in a React.Component just transparently calls out to `this.updater`[1] where `this.updater` is injected by the particular platform library (eg react-dom). At least in react-dom/server's case, a unique `updater` object exists per-component[2], so it's effectively a private instance field; and those state changes apply to a similarly per-component `inst.state`[3] You can also prove this by calling setState with the wrong `this`: `this.setState.call({}, {x:1})` blows up. So the `this` is required, unlike how `useState` works. [1]: https://github.com/facebook/react/blob/aa9423701e99a194d65a8b835882502902a65a50/packages/react/src/ReactBaseClasses.js#L66 https://github.com/facebook/react/blob/aa9423701e99a194d65a8... [2]: https://github.com/facebook/react/blob/aa9423701e99a194d65a8b835882502902a65a50/packages/react-dom/src/server/ReactPartialRenderer.js#L426 https://github.com/facebook/react/blob/aa9423701e99a194d65a8... [3]: https://github.com/facebook/react/blob/aa9423701e99a194d65a8b835882502902a65a50/packages/react-dom/src/server/ReactPartialRenderer.js#L607 https://github.com/facebook/react/blob/aa9423701e99a194d65a8...