[ReactNative] Add JS errors handling to iOS

Summary:
Every once in a while a guard is forgotten somewhere and the redbox is gone. I
want to remove the guards, but for that the stack traces have to be symbolicated
on the native side. So for now it just adds yet another check, in case a guard
is missing on JS.

React/Base/RCTBatchedBridge.m

@@ -239,7 +239,11 @@ RCT_NOT_IMPLEMENTED(-initWithBundleURL:(__unused NSURL *)bundleURL
   dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
   [_javaScriptExecutor injectJSONText:configJSON
                   asGlobalObjectNamed:@"__fbBatchedBridgeConfig" callback:
-   ^(__unused id err) {
+   ^(NSError *error) {
+     if (error) {
+       [[RCTRedBox sharedInstance] showError:error];
+     }
+
      dispatch_semaphore_signal(semaphore);
    }];
 
@@ -302,22 +306,21 @@ RCT_NOT_IMPLEMENTED(-initWithBundleURL:(__unused NSURL *)bundleURL
 
         [self enqueueApplicationScript:script url:bundleURL onComplete:^(NSError *loadError) {
 
-          if (!loadError) {
+          if (loadError) {
-
+            [[RCTRedBox sharedInstance] showError:loadError];
-            /**
+            return;
-             * Register the display link to start sending js calls after everything
-             * is setup
-             */
-            NSRunLoop *targetRunLoop = [_javaScriptExecutor isKindOfClass:[RCTContextExecutor class]] ? [NSRunLoop currentRunLoop] : [NSRunLoop mainRunLoop];
-            [_jsDisplayLink addToRunLoop:targetRunLoop forMode:NSRunLoopCommonModes];
-
-            [[NSNotificationCenter defaultCenter] postNotificationName:RCTJavaScriptDidLoadNotification
-                                                                object:_parentBridge
-                                                              userInfo:@{ @"bridge": self }];
-          } else {
-            [[RCTRedBox sharedInstance] showErrorMessage:[loadError localizedDescription]
-                                             withDetails:[loadError localizedFailureReason]];
           }
+
+          /**
+           * Register the display link to start sending js calls after everything
+           * is setup
+           */
+          NSRunLoop *targetRunLoop = [_javaScriptExecutor isKindOfClass:[RCTContextExecutor class]] ? [NSRunLoop currentRunLoop] : [NSRunLoop mainRunLoop];
+          [_jsDisplayLink addToRunLoop:targetRunLoop forMode:NSRunLoopCommonModes];
+
+          [[NSNotificationCenter defaultCenter] postNotificationName:RCTJavaScriptDidLoadNotification
+                                                              object:_parentBridge
+                                                            userInfo:@{ @"bridge": self }];
         }];
       }
     }];
@@ -527,7 +530,11 @@ RCT_NOT_IMPLEMENTED(-initWithBundleURL:(__unused NSURL *)bundleURL
 
   [[NSNotificationCenter defaultCenter] postNotificationName:RCTEnqueueNotification object:nil userInfo:nil];
 
-  RCTJavaScriptCallback processResponse = ^(id json, __unused NSError *error) {
+  RCTJavaScriptCallback processResponse = ^(id json, NSError *error) {
+    if (error) {
+      [[RCTRedBox sharedInstance] showError:error];
+    }
+
     if (!self.isValid) {
       return;
     }

React/Base/RCTRedBox.h

@@ -13,6 +13,7 @@
 
 + (instancetype)sharedInstance;
 
+- (void)showError:(NSError *)error;
 - (void)showErrorMessage:(NSString *)message;
 - (void)showErrorMessage:(NSString *)message withDetails:(NSString *)details;
 - (void)showErrorMessage:(NSString *)message withStack:(NSArray *)stack;

React/Base/RCTRedBox.m

@@ -283,6 +283,11 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
   _nextBackgroundColor = color;
 }
 
+- (void)showError:(NSError *)error
+{
+  [self showErrorMessage:error.localizedDescription withDetails:error.localizedFailureReason];
+}
+
 - (void)showErrorMessage:(NSString *)message
 {
   [self showErrorMessage:message withStack:nil showIfHidden:YES];
@@ -342,6 +347,7 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
 @implementation RCTRedBox
 
 + (instancetype)sharedInstance { return nil; }
+- (void)showError:(NSError *)message {}
 - (void)showErrorMessage:(NSString *)message {}
 - (void)showErrorMessage:(NSString *)message withDetails:(NSString *)details {}
 - (void)showErrorMessage:(NSString *)message withStack:(NSArray *)stack {}