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Example for loading new external data in response to updated props
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// 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 }); | |
} | |
}); | |
} | |
} |
Thanks for pointing out the typo. I often don't notice comments on Gists. I've updated the example.
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Yes, This will cause the second render to fail. Because
prevState
is having old data now.Blog post have the correct code