Mastering LWC Debugging: A Step-by-Step Guide

Debugging is an essential skill for any Salesforce developer working with Lightning Web Components (LWC). JavaScript, being a case-sensitive language, can often lead to errors that are tricky to identify. In this blog, we’ll explore the best practices, tools, and techniques to debug LWC components effectively. Whether you’re a beginner or an experienced developer, this guide will help you streamline your debugging process.

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Why Debugging LWC is Important

LWC components rely heavily on JavaScript, and even minor issues like variable case mismatches can cause errors. Debugging helps you identify and resolve these issues efficiently, ensuring your components function as expected. In this blog, we’ll cover:

• Configurations to simplify debugging.
• Browser and Salesforce settings for better performance.
• Techniques to debug JavaScript and wire decorators.
• Real-world debugging scenarios.

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1. Enable Debug Mode in Salesforce

The first step in debugging LWC components is enabling debug mode. This makes it easier to debug JavaScript code by providing detailed logs.

Steps to Enable Debug Mode:

1. Navigate to Setup in Salesforce.
2. Search for Debug Mode.
3. Enable debug mode for specific users who are actively debugging.
4. Important: Only enable debug mode in developer sandboxes or developer orgs, as it can impact performance.

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2. Disable Cache for Effective Debugging

Caching can cause issues during development, as changes in your code may not reflect immediately. Disabling cache ensures you see the latest updates without refreshing multiple times.

Steps to Disable Cache:

• From Salesforce:
  1. Go to Session Settings in Setup.
  2. Disable the option Enable Caching and Autocomplete on Login Page.
• From Browser:
  1. Open Developer Tools (right-click → Inspect).
  2. Go to the Network tab.
  3. Check the option Disable Cache.
• Optional: Use a browser extension like Clear Cache to clear the cache frequently.

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3. Disable Lightning Web Security

Lightning Web Security (LWS) can sometimes interfere with debugging. Disabling it temporarily in developer orgs or sandboxes can improve your debugging experience.

Steps to Disable Lightning Web Security:

1. Navigate to Session Settings in Setup.
2. Search for Lightning Web Security.
3. Disable it for better debugging.
4. Note: Do not disable this in production.

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4. Perform Empty Cache and Hard Reload

After making changes to your code, perform an empty cache and hard reload to ensure the latest updates are reflected.

Steps to Perform Hard Reload:

1. Open Developer Tools (right-click → Inspect).
2. Right-click on the browser’s refresh button.
3. Select Empty Cache and Hard Reload.

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5. Enable Custom Formatter

Custom formatters improve the readability of debugging logs, making it easier to identify issues.

Steps to Enable Custom Formatter:

1. Open Developer Tools (right-click → Inspect).
2. Click on the Settings icon (gear icon).
3. Under Preferences, scroll to Console.
4. Enable the option Custom Formatter.

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6. Add Framework Files to Ignore List

Framework-related files can clutter your debugging process with unnecessary exceptions. Adding these files to the ignore list helps you focus on your code.

Steps to Add Files to Ignore List:

1. Open Developer Tools (right-click → Inspect).
2. Navigate to the Ignore List under Settings.

3. The following patterns need to be added to the ignore list:

   1. /aura_prod.*.js$

   2. /components/.*.js$

4. Add custom exclusion rules to ignore framework files.

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7. Locate Your Source Code

To debug your LWC component, you need to locate its source code in the browser.

Steps to Locate Source Code:

1. Open Developer Tools (right-click → Inspect).
2. Navigate to the Sources tab.
3. Expand the Modules folder under SLDS to find your LWC components.
4. Open the desired component’s JavaScript or HTML file.
5. Shortcut: Use Ctrl + P to search for the component file directly.

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8. Debugging Using Breakpoints

Breakpoints allow you to pause code execution at specific lines, making it easier to inspect variables and functions.

Steps to Use Breakpoints:

1. Open the desired JavaScript file in the Sources tab.
2. Click on the line numbers to add breakpoints.
3. Use the following debugging controls:
   • F10: Step over to the next line.
   • F11: Step into a function.
   • Shift + F11: Step out of a function.
   • Play Button: Resume execution until the next breakpoint.

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9. Programmatic Breakpoints

You can also set breakpoints programmatically using the debugger keyword. This is especially useful when debugging in developer orgs or sandboxes.

Steps to Add Programmatic Breakpoints:

1. Add the debugger keyword in your JavaScript code where you want the execution to pause.
2. Deploy the code and refresh the page.
3. When the debugger keyword is encountered, the browser will pause execution automatically.

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10. Pause on Uncaught Exceptions

This feature automatically pauses execution when an error occurs, even if no breakpoints are set.

Steps to Enable Pause on Uncaught Exceptions:

1. Open Developer Tools (right-click → Inspect).
2. Navigate to the Sources tab.
3. Check the option Pause on Uncaught Exceptions.

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11. Debugging Wire Decorators

When using @wire decorators, ensure the data is being fetched correctly.

Steps to Debug Wire Decorators:

1. Add breakpoints in the JavaScript file where the @wire decorator is used.
2. Check the data being returned by hovering over the variables in the debugging panel.

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12. Debugging Input Validation

Input validation errors are common in LWC. Use breakpoints to inspect the validation logic and identify issues like case sensitivity or typos.

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13. Debugging Lifecycle Hooks

Add breakpoints in lifecycle hooks like connectedCallback or renderedCallback to ensure they are being executed as expected.

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14. Styling Debugging

Use the Elements tab in the browser’s Developer Tools to:

• Inspect and modify styles directly.
• Test changes like font size or color without redeploying the code.

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15. Real-World Debugging Scenarios

Scenario 1: Debugging a Create Account Button

• Issue: Clicking the button does nothing.
• Solution:
  1. Add breakpoints in the clickHandler method.
  2. Step through the code to identify issues (e.g., variable case mismatch like valid vs. Valid).
  3. Use the Pause on Uncaught Exceptions option to catch errors automatically.

Scenario 2: Debugging a Wire Decorator

• Issue: Data is not displayed based on user input.
• Solution:
  1. Add breakpoints in the @wire decorator function.
  2. Check the data being returned by hovering over variables.
  3. Correct any issues in the logic (e.g., incorrect method names or case sensitivity).

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Conclusion

Debugging LWC components can seem daunting at first, but with the right tools and techniques, it becomes a systematic and efficient process. By following the steps outlined in this guide, you’ll be able to identify and resolve issues quickly, ensuring your components work flawlessly.