a component is mounted twice

bug

What is the current behavior?

For the same component, componentDidMount is called multiple times, without calling componentWillUnmount , when using ReactDOM.unmountComponentAtNode .

You can use the link below to reproduce it:

https://codesandbox.io/s/x76mlw16rp

What is the expected behavior?

componentWillUnmount should be called before calling componentDidMount again.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

16.x

[michael8090]

Yes, I checked yesterday and saw the legacyRenderSubtreeIntoContainer scheduled an unmout task and the callback () => container._reactRootContainer = null was set, but the following forceUpdate(triggered by ReactDOM.unstable_batchedUpdates(() => this.refs.a.forceUpdate()) somehow cancelled the real unmount task without removing the callback (that’s the root cause). The component did a regular update due to the forceUpdate, and the callback was called, resulting in the following updating logic thinking it was a fresh initial mount.

[gaearon]

I would look for suspicious race conditions around here

https://github.com/facebook/react/blob/d3bbfe09cc47e2c5e34c3f5d0373e726981f0919/packages/react-dom/src/client/ReactDOM.js#L681-L688

https://github.com/facebook/react/blob/d3bbfe09cc47e2c5e34c3f5d0373e726981f0919/packages/react-dom/src/client/ReactDOM.js#L524-L550