fix(ts): onScroll event type (#1631)

* Fix onScroll event type

* Update documentation

* Address PR feedback

docs/Reference.md

@@ -22,6 +22,7 @@ This document lays out the current public properties and methods for the React N
 - [`onMessage`](Reference.md#onmessage)
 - [`onNavigationStateChange`](Reference.md#onnavigationstatechange)
 - [`onContentProcessDidTerminate`](Reference.md#oncontentprocessdidterminate)
+- [`onScroll`](Reference.md#onscroll)
 - [`originWhitelist`](Reference.md#originwhitelist)
 - [`renderError`](Reference.md#rendererror)
 - [`renderLoading`](Reference.md#renderloading)
@@ -580,6 +581,39 @@ url
 
 ---
 
+### `onScroll`[⬆](#props-index)<!-- Link generated with jump2header -->
+
+Function that is invoked when the scroll event is fired in the `WebView`.
+
+| Type     | Required | Platform                |
+| -------- | -------- | ----------------------- |
+| function | No       | iOS, macOS, Android, Windows |
+
+Example:
+
+```jsx
+<Webview
+  source={{ uri: 'https://reactnative.dev' }}
+  onScroll={syntheticEvent => {
+    const { contentOffset } = syntheticEvent.nativeEvent
+    console.table(contentOffset)
+  }}
+/>
+```
+
+Function passed to `onScroll` is called with a SyntheticEvent wrapping a nativeEvent with these properties:
+
+```
+contentInset
+contentOffset
+contentSize
+layoutMeasurement
+velocity
+zoomScale
+```
+
+---
+
 ### `originWhitelist`[⬆](#props-index)<!-- Link generated with jump2header -->
 
 List of origin strings to allow being navigated to. The strings allow wildcards and get matched against _just_ the origin (not the full URL). If the user taps to navigate to a new page but the new page is not in this whitelist, the URL will be handled by the OS. The default whitelisted origins are "http://*" and "https://*".

src/WebViewTypes.ts

@@ -167,6 +167,8 @@ export type WebViewHttpErrorEvent = NativeSyntheticEvent<WebViewHttpError>;
 
 export type WebViewRenderProcessGoneEvent = NativeSyntheticEvent<WebViewRenderProcessGoneDetail>;
 
+export type WebViewScrollEvent = NativeSyntheticEvent<NativeScrollEvent>;
+
 export type DataDetectorTypes =
   | 'phoneNumber'
   | 'link'
@@ -259,7 +261,7 @@ export interface CommonNativeWebViewProps extends ViewProps {
   javaScriptCanOpenWindowsAutomatically?: boolean;
   mediaPlaybackRequiresUserAction?: boolean;
   messagingEnabled: boolean;
-  onScroll?: (event: NativeScrollEvent) => void;
+  onScroll?: (event: WebViewScrollEvent) => void;
   onLoadingError: (event: WebViewErrorEvent) => void;
   onLoadingFinish: (event: WebViewNavigationEvent) => void;
   onLoadingProgress: (event: WebViewProgressEvent) => void;
@@ -921,7 +923,7 @@ export interface WebViewSharedProps extends ViewProps {
   /**
    * Function that is invoked when the `WebView` scrolls.
    */
-  onScroll?: (event: NativeScrollEvent) => void;
+  onScroll?: (event: WebViewScrollEvent) => void;
 
   /**
    * Function that is invoked when the `WebView` has finished loading.