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How to Resolve "DevTools failed to load SourceMap" for a Chrome Extension

When working in the Chrome DevTools, you may encounter console warnings like DevTools failed to load SourceMap: Could not load content for chrome-extension://.... These messages are generally harmless but can add distracting noise to your console, making it harder to debug your own code.

This guide will explain what this warning means and provide three practical solutions to resolve it, from disabling the feature globally to identifying the specific extension causing the problem.

What is a Source Map and Why Does This Warning Appear?​

A source map is a file that maps a compressed, minified, or bundled file (like main.min.js) back to its original, uncompressed source code. This is a crucial tool for debugging production code, as it allows the browser to show you readable, original code instead of the minified version.

The warning DevTools failed to load SourceMap... appears when:

  1. A piece of code (often from a Chrome extension you have installed) includes a comment pointing to a source map file.
  2. The browser's DevTools tries to download that .map file to help with debugging.
  3. The file is missing or inaccessible, resulting in an HTTP error (like a 404).

Because these warnings are generated by third-party extensions, you cannot fix their code. However, you can configure your DevTools to ignore these requests.

For most web developers who are not actively debugging Chrome extensions, the simplest and most effective solution is to disable the source map feature in the DevTools settings. This will stop the browser from trying to fetch these missing files.

Solution:

  1. Open Chrome DevTools (press F12 or right-click the page and select "Inspect").
  2. Click the Cogwheel icon in the top-right corner to open the Settings panel.
  3. In the Preferences tab, find the Sources section.
  4. Uncheck the following two boxes:
    • Enable JavaScript source maps
    • Enable CSS source maps
  5. Close the settings panel and refresh your page. The warnings will be gone.

This is the recommended approach as it has no negative impact on your own web development workflow unless you are specifically working with source maps from your own build tools.

Solution 2: Filter Out Extension Messages​

If you prefer not to disable source maps globally, you can use the Console's filter settings to hide messages that don't originate from your own code.

Solution:

  1. Open the Chrome DevTools and go to the Console tab.
  2. Click the Cogwheel icon in the top-right corner of the Console panel itself (this is different from the main DevTools settings).
  3. Check the box for Selected context only.

This setting filters the console to show logs only from the current document's context (e.g., your webpage), hiding noise from extensions and other sources.

Solution 3: Identify and Disable the Problematic Extension​

If you want to stop the warnings at their source, you can try to identify which extension is causing them and disable it.

Solution:

  1. In Chrome, navigate to chrome://extensions or click the puzzle icon in the toolbar and select Manage Extensions.
  2. One by one, disable each extension by toggling the switch off.
  3. After disabling an extension, return to your webpage, refresh it with the DevTools open, and check if the warning has disappeared.
  4. Repeat this process until you find the extension that is generating the source map errors.

Once you find the culprit, you can choose to keep it disabled or contact the extension's developer to report the issue.

Conclusion​

The "DevTools failed to load SourceMap" warning is a common and generally harmless message caused by Chrome extensions.

  • The quickest and most recommended solution for most developers is to disable JavaScript and CSS source maps in the DevTools settings.
  • Alternatively, you can filter your console to show the "Selected context only" to hide the noise.
  • If the warnings persist and bother you, you can perform a process of elimination to identify and disable the specific extension causing the issue.

By applying these simple configuration changes, you can clean up your console and focus on debugging your own application.

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