Sometimes console.log shows in log-ios sometimes it doesn't

Question

I have run react-native start in one terminal, and then react-native ios-run in another. My initial console.log rarely show, sometimes

Answer 1

i found that the JavascriptCore engine won't automatically redirect the console.log to either XCode output panel or the system builtin Console.App， not to mention the self-broken log-ios command.

the only way to see console.log without remote debugging in browser is redirect(bind) it ourselves:

//Add this headers
#import 
#import 
#import 
...
...

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

  NSURL *jsCodeLocation;
  ...
  ...
  [self.window makeKeyAndVisible];


  ::sleep(2); //<---!!!!!see below

  JSGlobalContextRef globalContext = rootView.bridge.jsContextRef;
  JSContext *context = [JSC_JSContext(globalContext) contextWithJSGlobalContextRef:globalContext];
  context[@"console"][@"log"] = ^(NSString *message) {
    NSLog(@"Javascript log: %@",message);
  };
  return YES;
}

Caution: the JSContext within reactInstance is created in another thread, I don't know how to get the loaded event(in only my project, since i don't like to modify the react-native engine), just wait sometime here for testing purpose.