[change] Image - handle cases where the source object only changes by reference

When the source object changed by reference, but stays structurally the same
we should do nothing and not trigger the loading effect again

Author: kidroca

packages/react-native-web/src/exports/Image/__tests__/index-test.js

@@ -432,6 +432,21 @@ describe('components/Image', () => {
         expect.any(Function)
       );
     });
+
+    // A common case is `source` declared as an inline object, which cause is to be a
+    // new object (with the same content) each time parent component renders
+    test('it still loads the image if source object is changed', () => {
+      ImageLoader.load.mockImplementation(() => {});
+
+      const releaseSpy = jest.spyOn(ImageLoader, 'release');
+
+      const uri = 'https://google.com/favicon.ico';
+      const { rerender } = render(<Image source={{ uri }} />);
+      rerender(<Image source={{ uri }} />);
+
+      // when the underlying source didn't change we expect the initial request is not cancelled due to re-render
+      expect(releaseSpy).not.toHaveBeenCalled();
+    });
   });
 
   describe('prop "style"', () => {

packages/react-native-web/src/exports/Image/index.js

@@ -8,7 +8,7 @@
  * @flow
  */
 
-import type { ImageProps } from './types';
+import type { ImageProps, Source } from './types';
 
 import * as React from 'react';
 import createElement from '../createElement';
@@ -317,9 +317,10 @@ type UseSourceParams = {
 const useSource = (
   { onLoad, onLoadStart, onLoadEnd, onError }: UseSourceParams,
   source: ?Source
-): { state: string, uri: string } => {
+): { state: string, loadedUri: string } => {
+  const lastLoadedSource = React.useRef();
   const [loadedUri, setLoadedUri] = React.useState('');
-  const [state, updateState] = React.useState(() => {
+  const [state, setState] = React.useState(() => {
     const uri = resolveAssetUri(source);
     if (uri != null) {
       const isLoaded = ImageLoader.has(uri);
@@ -328,39 +329,50 @@ const useSource = (
     return IDLE;
   });
 
-  const loadInput = React.useRef(null);
-
-  React.useEffect(() => {
+  // This object would only change when load related fields change
+  // We try to maintain strict object reference to prevent the effect hook running due to object change
+  const stableSource = React.useMemo(() => {
     const uri = resolveAssetUri(source);
-    if (uri == null) return;
+    if (uri == null) {
+      lastLoadedSource.current = null;
+      return null;
+    }
 
     let headers;
     if (source && typeof source.headers === 'object') {
       headers = ((source.headers: any): { [key: string]: string });
     }
 
     const nextInput = { uri, headers };
-    const currentInput = loadInput.current;
-    if (JSON.stringify(nextInput) === JSON.stringify(currentInput)) return;
+    if (
+      JSON.stringify(nextInput) !== JSON.stringify(lastLoadedSource.current)
+    ) {
+      lastLoadedSource.current = nextInput;
+    }
+
+    return lastLoadedSource.current;
+  }, [source]);
+
+  React.useEffect(() => {
+    if (stableSource == null) return;
 
-    updateState(LOADING);
+    setState(LOADING);
     if (onLoadStart) onLoadStart();
 
-    loadInput.current = nextInput;
     const requestId = ImageLoader.load(
-      nextInput,
+      stableSource,
       function load(result) {
-        updateState(LOADED);
+        setState(LOADED);
         setLoadedUri(result.uri);
         if (onLoad) onLoad(result);
         if (onLoadEnd) onLoadEnd();
       },
       function error() {
-        updateState(ERRORED);
+        setState(ERRORED);
         if (onError) {
           onError({
             nativeEvent: {
-              error: `Failed to load resource ${uri} (404)`
+              error: `Failed to load resource ${stableSource.uri} (404)`
             }
           });
         }
@@ -370,7 +382,7 @@ const useSource = (
 
     const effectCleanup = () => ImageLoader.release(requestId);
     return effectCleanup;
-  }, [updateState, onError, onLoad, onLoadEnd, onLoadStart, source]);
+  }, [onError, onLoad, onLoadEnd, onLoadStart, stableSource]);
 
   return {
     state,