SourceMap Header

Table of Content

The SourceMap header is a crucial component in web development. It serves as a mapping utility that aids in the debugging process. By pointing to a source map, it simplifies the process of tracing errors or bugs back to the original, unaltered code, making it easier to handle and rectify them. This is particularly important when dealing with minified or consolidated JavaScript or CSS files, where the resultant code doesn't resemble the original codebase.




There are two main directives for SourceMap:

  • sourceMappingURL: This specifies the URL at which the source map file can be found.
  • sourceContent: This maps the original source code to the relevant location in the transpiled code.


To use a SourceMap header, you append it to the end of your JavaScript file.

// Some JavaScript code
console.log('Hello World!');

// At the end of your file

Browser Compatibility

Browser Compatibility
Chrome Supported
Firefox Supported
Safari Not Supported
Opera Supported
Edge Supported

How to modify SourceMap header

The ModHeader Chrome extension is a powerful tool to view and modify HTTP request headers. To modify the SourceMap header using ModHeader, follow these steps:

  1. Install the ModHeader extension from the Chrome Web Store.
  2. Click on the ModHeader icon to open the extension.
  3. Click on 'Add', then 'Request headers.'
  4. In the 'Name' field, type 'SourceMap.'
  5. In the 'Value' field, type the URL of the source map.

This allows you to change the source map URL on the fly, aiding in testing and debugging different versions of source maps without changing the server's code. This can be extremely helpful in the process of debugging and improving your application's performance, particularly when dealing with more complex or larger scale projects.