If using the new style context, re-declare this in your class to be the
React.ContextType
of your static contextType
.
Should be used with type annotation or static contextType.
static contextType = MyContext
// For TS pre-3.7:
context!: React.ContextType<typeof MyContext>
// For TS 3.7 and above:
declare context: React.ContextType<typeof MyContext>
Readonly
propsStatic
Optional
contextIf set, this.context
will be set at runtime to the current value of the given Context.
Usage:
type MyContext = number
const Ctx = React.createContext<MyContext>(0)
class Foo extends React.Component {
static contextType = Ctx
context!: React.ContextType<typeof Ctx>
render () {
return <>My context's value: {this.context}</>;
}
}
Optional
UNSAFE_Called immediately before mounting occurs, and before Component#render
.
Avoid introducing any side-effects or subscriptions in this method.
This method will not stop working in React 17.
Note: the presence of getSnapshotBeforeUpdate or getDerivedStateFromProps prevents this from being invoked.
16.3, use componentDidMount or the constructor instead
Optional
UNSAFE_Called when the component may be receiving new props. React may call this even if props have not changed, so be sure to compare new and existing props if you only want to handle changes.
Calling Component#setState
generally does not trigger this method.
This method will not stop working in React 17.
Note: the presence of getSnapshotBeforeUpdate or getDerivedStateFromProps prevents this from being invoked.
16.3, use static getDerivedStateFromProps instead
Optional
UNSAFE_Called immediately before rendering when new props or state is received. Not called for the initial render.
Note: You cannot call Component#setState
here.
This method will not stop working in React 17.
Note: the presence of getSnapshotBeforeUpdate or getDerivedStateFromProps prevents this from being invoked.
16.3, use getSnapshotBeforeUpdate instead
Optional
componentOptional
componentCalled immediately after updating occurs. Not called for the initial render.
The snapshot is only present if getSnapshotBeforeUpdate is present and returns non-null.
Optional
snapshot: anyOptional
componentCalled immediately before mounting occurs, and before Component#render
.
Avoid introducing any side-effects or subscriptions in this method.
Note: the presence of getSnapshotBeforeUpdate or getDerivedStateFromProps prevents this from being invoked.
16.3, use componentDidMount or the constructor instead; will stop working in React 17
Optional
componentCalled when the component may be receiving new props. React may call this even if props have not changed, so be sure to compare new and existing props if you only want to handle changes.
Calling Component#setState
generally does not trigger this method.
Note: the presence of getSnapshotBeforeUpdate or getDerivedStateFromProps prevents this from being invoked.
16.3, use static getDerivedStateFromProps instead; will stop working in React 17
Optional
componentCalled immediately before rendering when new props or state is received. Not called for the initial render.
Note: You cannot call Component#setState
here.
Note: the presence of getSnapshotBeforeUpdate or getDerivedStateFromProps prevents this from being invoked.
16.3, use getSnapshotBeforeUpdate instead; will stop working in React 17
Optional
getRuns before React applies the result of render
to the document, and
returns an object to be given to componentDidUpdate. Useful for saving
things such as scroll position before render
causes changes to it.
Note: the presence of getSnapshotBeforeUpdate prevents any of the deprecated lifecycle events from running.
Optional
callback: (() => void)Optional
shouldCalled to determine whether the change in props and state should trigger a re-render.
Component
always returns true.
PureComponent
implements a shallow comparison on props and state and returns true if any
props or states have changed.
If false is returned, Component#render
, componentWillUpdate
and componentDidUpdate
will not be called.
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