title: how to debug when react native app doesnt start on ios device
body: <p>when I start the react-native app, it always starts, as long as I have it connected to the mac.</p>
  
  <p>As soon as I disconnect the iphone, the app mostly hangs on startup and crashes, without any further error messages.
  But, other errors will show up on the screen (red and yellow flagged errors).</p>
  
  <p>When I doubleclick the homebutton, strangely, the app seems to be in a started state, but I am not able to switch to it.</p>
  
  <p>How can you debug best such a behavior and find the the things causing the strange startup behavior?</p>
  
  <p>Update:</p>
  
  <p>I found those errors</p>
  
  <pre><code>2016-08-08 16:25:23.604 [warn][tid:main][RCTEventEmitter.m:54] Sending `websocketFailed` with no listeners registered.
  2016-08-08 16:25:23.612113 PhoenixApp[525:64778] Sending `websocketFailed` with no listeners registered.
  2016-08-08 16:25:23.742 [warn][tid:com.facebook.react.JavaScript] The regenerator/runtime module is deprecated; please import regenerator-runtime/runtime instead.
  2016-08-08 16:25:23.741927 PhoenixApp[525:65027] The regenerator/runtime module is deprecated; please import regenerator-runtime/runtime instead.
  2016-08-08 16:25:23.860 [info][tid:com.facebook.react.JavaScript] Running application "PhoenixApp" with appParams: {"rootTag":1,"initialProps":{}}. __DEV__ === true, development-level warning are ON, performance optimizations are OFF
  2016-08-08 16:25:23.860251 PhoenixApp[525:65027] Running application "PhoenixApp" with appParams: {"rootTag":1,"initialProps":{}}. __DEV__ === true, development-level warning are ON, performance optimizations are OFF
  2016-08-08 16:25:24.139 [info][tid:com.facebook.react.JavaScript] null
  2016-08-08 16:25:24.138808 PhoenixApp[525:65027] null
  </code></pre>
  
  <p>followed by (each second)</p>
  
  <pre><code>2016-08-08 16:31:43.159749 PhoenixApp[525:64956] [] __nw_connection_get_connected_socket_block_invoke 176 Connection has no connected handler
  2016-08-08 16:31:45.372329 PhoenixApp[525:65445] [] __nw_connection_get_connected_socket_block_invoke 177 Connection has no connected handler
  2016-08-08 16:31:47.575208 PhoenixApp[525:64955] [] __nw_connection_get_connected_socket_block_invoke 178 Connection has no connected handler
  2016-08-08 16:31:49.788935 PhoenixApp[525:65445] [] __nw_connection_get_connected_socket_block_invoke 179 Connection has no connected handler
  2016-08-08 16:31:51.970877 PhoenixApp[525:64955] [] __nw_connection_get_connected_socket_block_invoke 180 Connection has no connected handler
  2016-08-08 16:31:54.173791 PhoenixApp[525:65445] [] __nw_connection_get_connected_socket_block_invoke 181 Connection has no connected handler
  </code></pre>
  
  <p>AppDelegate.m</p>
  
  <pre><code>/**
   * Copyright (c) 2015-present, Facebook, Inc.
   * All rights reserved.
   *
   * This source code is licensed under the BSD-style license found in the
   * LICENSE file in the root directory of this source tree. An additional grant
   * of patent rights can be found in the PATENTS file in the same directory.
   */
  
  #import "AppDelegate.h"
  
  #import "RCTBundleURLProvider.h"
  #import "RCTRootView.h"
  
  @implementation AppDelegate
  
  - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
    NSURL *jsCodeLocation;
  
    [[RCTBundleURLProvider sharedSettings] setDefaults];
    jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index.ios" fallbackResource:nil];
  
    RCTRootView *rootView = [[RCTRootView alloc] initWithBundleURL:jsCodeLocation
                                                        moduleName:@"PhoenixTrello"
                                                 initialProperties:nil
                                                     launchOptions:launchOptions];
    rootView.backgroundColor = [[UIColor alloc] initWithRed:1.0f green:1.0f blue:1.0f alpha:1];
  
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    UIViewController *rootViewController = [UIViewController new];
    rootViewController.view = rootView;
    self.window.rootViewController = rootViewController;
    [self.window makeKeyAndVisible];
    return YES;
  }
  
  @end
  </code></pre>
  
  <p>setup:</p>
  
  <p>react-native-cli: 1.0.0
  react-native: 0.32.0-rc.0
  react: 15.3.0</p>
  
  <p>Xcode 8 beta 4, iOS 10</p>