React Native Debug u0026 Fix: Interview Challenge Quiz Quiz

Sharpen your ability to troubleshoot and resolve common React Native issues with this quiz designed to test knowledge of debugging techniques, common pitfalls, and problem-solving strategies in real-world scenarios. Improve your interview readiness by assessing your skills in navigating and fixing typical React Native development challenges.

1. Fixing Red Screen Errors

   When a React Native app shows a red screen with the error 'Undefined is not a function' after a recent code change, what is the most likely cause?

   1. The app has run out of memory.
   2. There is a missing stylesheet property.
   3. The device battery is low.
   4. A JavaScript method or import does not exist or is misspelled.

   Explanation: A red screen with 'Undefined is not a function' usually means you are calling a function that is undefined, often due to a misspelled import or incorrect method reference. Memory issues typically cause slowdowns or crashes, not this error. A missing stylesheet property would cause layout problems, not this message. Low device battery would not generate this error in the app.

2. Image Not Displayed

   If an image component in a React Native app is not showing any picture, but the source URI looks correct, which simple mistake could cause this?

   1. The package.json file is missing.
   2. The image style width and height are not set.
   3. The AndroidManifest.xml is incorrect.
   4. The component name is capitalized.

   Explanation: In React Native, images require explicit width and height; otherwise, nothing will be rendered even if the URI is correct. Missing a package.json would prevent the entire project from working, which is a broader issue. AndroidManifest.xml mainly deals with native configuration, not image display. Component name capitalization is important for components but does not directly affect image display.

3. App Not Reloading Changes

   After saving file changes in a React Native project, the updates are not visible in the app even after triggering a refresh. What could be the main cause?

   1. The Metro bundler needs to be restarted.
   2. The device is in airplane mode.
   3. There is a typo in a color value.
   4. The app lacks a manifest file.

   Explanation: Sometimes the Metro bundler, which serves your app's code, can crash or become unresponsive, causing code changes not to appear after refreshing. Airplane mode would affect networking, not code updates. Lack of a manifest file would prevent the app from running entirely. Typo in a color value may cause a visual issue, but would not stop refreshes from working.

4. Debugging Press Events

   A button in your React Native app is visibly rendered but does not respond when pressed. What is a likely cause for this problem?

   1. There are too many console logs.
   2. The button's onPress prop is missing or incorrect.
   3. The button text is too long.
   4. The JavaScript bundle size is too large.

   Explanation: A button needs a correct onPress property with a function to respond to user touches. Large bundle sizes can cause performance issues but not direct unresponsiveness. The length of button text and the number of console logs do not affect whether press events work.

5. Resolving Network Requests

   Suppose a fetch request to a remote API from your React Native app never completes, remaining stuck in a loading state. What is the most likely basic issue?

   1. The device screen brightness is too low.
   2. The app icon file is too large.
   3. The app does not have internet permission.
   4. The font family is not supported.

   Explanation: For network requests to work, the app must have explicit internet permissions configured, especially on mobile devices. Screen brightness and font support do not impact network connectivity. App icon file size could affect installation or performance but not networking.

6. Handling Unresponsive UI Updates

   If tapping a switch component in a React Native app does not toggle its visual value, what coding mistake is most probable?

   1. The project uses an old version of JavaScript.
   2. Too many images are loaded in the view.
   3. The current value state is not updated in the onValueChange handler.
   4. Incorrect padding is set for the switch.

   Explanation: For controlled components like switches, not updating the state controlling the 'value' property will result in no visual change. JavaScript version or padding settings would not prevent the switch from visually toggling. Having many images could slow the app but not affect the logic of the switch.

7. App Crash on Start

   If a React Native app crashes immediately on startup after adding a new native dependency, what is one likely cause?

   1. There are unused variables in the code.
   2. Style files are missing colors.
   3. The native module was not properly linked or installed.
   4. The build folder was not deleted.

   Explanation: Improper linking or installation of native modules often causes instant app crashes due to missing files or configuration. Unused variables or missing colors in styles would not cause startup crashes. Not deleting the build folder can cause outdated builds but is less likely to cause a crash outright compared to misconfigured dependencies.

8. Syntax Error Detection

   You see a red screen with the message 'Unexpected token' or 'Unexpected end of input' after editing a JavaScript file in your React Native project. What does this indicate?

   1. There is a syntax error in the JavaScript code.
   2. The splash screen image is missing.
   3. The device storage is full.
   4. The flex direction style is incorrect.

   Explanation: Messages like 'Unexpected token' or 'Unexpected end of input' point to a syntax mistake such as a missing bracket or incorrect punctuation. Full device storage and missing splash images are unrelated to this error type. Style issues, including flex direction, could affect layout but not cause syntax errors.

9. List Rendering Issue

   If a FlatList in a React Native app does not render any items even though the data array is populated correctly, what common mistake should you look for?

   1. The padding of the list is negative.
   2. The keyExtractor prop is not defined or is incorrect.
   3. The View component lacks a border.
   4. The screen brightness is too high.

   Explanation: FlatList needs a correct keyExtractor to identify each item uniquely; omitting or misconfiguring it can lead to rendering issues. A View's border or padding does not prevent items from appearing, though it can affect appearance. Screen brightness settings are unrelated to FlatList behavior.

10. Text Input Not Updating

    A TextInput field in a React Native form always remains empty, no matter what the user types. What simple code mistake could cause this?

    1. Too many style properties are applied.
    2. The input border color is incorrect.
    3. The form does not have a label.
    4. The value prop is set but the onChangeText handler does not update state.

    Explanation: When using controlled components like TextInput, the value must be updated as the user types; otherwise, the field will not reflect changes. Incorrect border color, missing label, or styling issues will not prevent the input from updating its text. The key lies in connecting user input to up-to-date state.