JavaScript sources are often combined and minified to make delivering them from the server more efficient. Increasingly, too, JavaScript running in a page is machine-generated, as when compiled from a language like CoffeeScript or TypeScript. By using source maps, the debugger can map the code being executed to the original source files, making debugging much, much easier.
By default, the Debugger will use source maps if they are available. To check whether source map support is enabled, or to disable it if you need to, click the "Debugger Options" button and see the "Show Original Sources" entry in the list of settings that pops up:
Of course, for this to work, you will need to have supplied a source map for the JavaScript running in the page. Do this by appending a comment directive to your source file:
//# sourceMappingURL=https://example.com/path/to/your/sourcemap.map