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Example for loading new external data in response to updated props
// This is an example of how to fetch external data in response to updated props,
// If you are using an async mechanism that does not support cancellation (e.g. a Promise).
class ExampleComponent extends React.Component {
_currentId = null;
state = {
externalData: null
};
static getDerivedStateFromProps(nextProps, prevState) {
// Store prevId in state so we can compare when props change.
// Clear out previously-loaded data (so we don't render stale stuff).
if (nextProps.id !== prevState.prevId) {
return {
externalData: null,
prevId: nextProps.id
};
}
// No state update necessary
return null;
}
componentDidMount() {
this._loadAsyncData(this.props.id);
}
componentDidUpdate(prevProps, prevState) {
if (this.state.externalData === null) {
this._loadAsyncData(this.props.id);
}
}
componentWillUnmount() {
// Prevent potential setState calls after unmount,
// (Since these trigger DEV warnigs)
_currentId = null;
}
render() {
if (this.state.externalData === null) {
// Render loading state ...
} else {
// Render real UI ...
}
}
_loadAsyncData(id) {
if (id === this._currentId) {
// Data for this id is already loading
}
this._currentId = id;
asyncLoadData(id).then(externalData => {
// Only update state if the Promise that has just resolved,
// Reflects the most recently requested external data.
if (id === this._currentId) {
this.setState({ externalData });
}
});
}
}
@khanhlu2013
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khanhlu2013 commented Jul 18, 2018

What about if we remove static getDerivedStateFromProps method all together, and update componentDidUpdate as follow:

componentDidUpdate(prevProps){
  if(this.props.id !== prevProps.id){
    this.setState({externalData:null});
    this._loadAsyncData(this.props.id);
  }
}

@akonsu
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akonsu commented Jul 25, 2018

A bug:

componentDidUpdate(prevProps, prevState) {
    if (prevState.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

must read

componentDidUpdate(prevProps, prevState) {
    if (this.state.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

@Nico142
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Nico142 commented Aug 23, 2018

I thought the same as @khanhlu2013. Is there a reason why you used getDerivedStateFromProps instead of comparing the IDs (this.props.id !== prevProps.id) in componentDidUpdate?

@tranvansang
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tranvansang commented Jan 29, 2019

shouldn't asyncLoadData catch error?

    asyncLoadData(id).then(externalData => {
      // Only update state if the Promise that has just resolved,
      // Reflects the most recently requested external data.
      if (id === this._currentId) {
        this.setState({ externalData });
      }
    });

should be

    asyncLoadData(id).then(externalData => {
      // Only update state if the Promise that has just resolved,
      // Reflects the most recently requested external data.
      if (id === this._currentId) {
        this.setState({ externalData });
      }
    }).catch(() => this._currentId = null);

@kasajian
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kasajian commented Mar 9, 2019

akonsu's change is required.
inomdzhon's change is required.

If the author isn't going to update the gist, could someone else create a new one, along with a online running example?

@aidanlister
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aidanlister commented Mar 12, 2019

@Stephen-ONeil I feel the same way, if (id === this._currentId) { is basically just an isMounted check ...

@tmkasun
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tmkasun commented Aug 9, 2019

A bug:

componentDidUpdate(prevProps, prevState) {
    if (prevState.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

must read

componentDidUpdate(prevProps, prevState) {
    if (this.state.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

Yes, This will cause the second render to fail. Because prevState is having old data now.

Blog post have the correct code

@bvaughn
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Author

bvaughn commented Aug 9, 2019

Thanks for pointing out the typo. I often don't notice comments on Gists. I've updated the example.

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