Fix NativeSyntheticEvent compatibility with BaseSyntheticEvent

packages/react-native/Libraries/Types/CoreEventTypes.js

@@ -11,24 +11,24 @@
 import type {HostInstance} from '../../src/private/types/HostInstance';
 
 export type NativeSyntheticEvent<out T> = Readonly<{
-  bubbles: ?boolean,
-  cancelable: ?boolean,
+  bubbles: boolean,
+  cancelable: boolean,
   currentTarget: number | HostInstance,
-  defaultPrevented: ?boolean,
+  defaultPrevented: boolean,
   dispatchConfig: Readonly<{
     registrationName: string,
   }>,
-  eventPhase: ?number,
+  eventPhase: number,
   preventDefault: () => void,
   isDefaultPrevented: () => boolean,
   stopPropagation: () => void,
   isPropagationStopped: () => boolean,
-  isTrusted: ?boolean,
+  isTrusted: boolean,
   nativeEvent: T,
   persist: () => void,
   target: ?number | HostInstance,
   timeStamp: number,
-  type: ?string,
+  type: string,
 }>;
 
 export type ResponderSyntheticEvent<T> = Readonly<{

packages/react-native/ReactNativeApi.d.ts

@@ -3180,19 +3180,19 @@ declare type NativeScrollVelocity = {
   readonly y: number
 }
 declare type NativeSyntheticEvent<T> = {
-  readonly bubbles: boolean | undefined
-  readonly cancelable: boolean | undefined
+  readonly bubbles: boolean
+  readonly cancelable: boolean
   readonly currentTarget: HostInstance | number
-  readonly defaultPrevented: boolean | undefined
+  readonly defaultPrevented: boolean
   readonly dispatchConfig: {
     readonly registrationName: string
   }
-  readonly eventPhase: number | undefined
-  readonly isTrusted: boolean | undefined
+  readonly eventPhase: number
+  readonly isTrusted: boolean
   readonly nativeEvent: T
   readonly target: (number | undefined) | HostInstance
   readonly timeStamp: number
-  readonly type: string | undefined
+  readonly type: string
   readonly isDefaultPrevented: () => boolean
   readonly isPropagationStopped: () => boolean
   readonly persist: () => void

packages/react-native/__typetests__/index.tsx

@@ -391,6 +391,9 @@ processColor(Symbol('test'));
 const testNativeSyntheticEvent = <T extends {}>(
   e: NativeSyntheticEvent<T>,
 ): void => {
+  const baseEvent: React.BaseSyntheticEvent = e;
+  baseEvent.preventDefault();
+
   e.isDefaultPrevented();
   e.preventDefault();
   e.isPropagationStopped();