The source map file is used by chrome debugger to help developers debug the minified script file...
The idea is when you build for production, along with minifying and combining your JavaScript files, you generate a source map which holds information about your original files. When you query a certain line and column number in your generated JavaScript you can do a lookup in the source map which returns the original location. The DevTools can parse the source map automatically and make it appear as though you're running unminified and uncombined files.
So the map
file is loaded only when the debugger is active... meaning the file will be loaded only on dev environment not in the users systems