what are the .map files used for in Bootstrap 3.x?

There are two files included in the CSS folder with .map file extensions. They are:

bootstrap-theme.css.map
bootstrap.css.map

They appear to be minified files but I don't know what they are for.

Solution 1:

From Working with CSS preprocessors in Chrome DevTools:

Many developers generate CSS style sheets using a CSS preprocessor, such as Sass, Less, or Stylus. Because the CSS files are generated, editing the CSS files directly is not as helpful.

For preprocessors that support CSS source maps, DevTools lets you live-edit your preprocessor source files in the Sources panel, and view the results without having to leave DevTools or refresh the page. When you inspect an element whose styles are provided by a generated CSS file, the Elements panel displays a link to the original source file, not the generated .css file.

Solution 2:

If you just want to get rid of the error, you can also delete this line in bootstrap.css:

/*# sourceMappingURL=bootstrap.css.map */

Solution 3:

These are source maps. Provide these alongside compressed source files; developer tools such as those in Firefox and Chrome will use them to allow debugging as if the code was not compressed.

Solution 4:

The bootstrap css can be generated by Less. The main purpose of map file is used to link the css source code to less source code in the chrome dev tool. As we used to do .If we inspect the element in the chrome dev tool. you can see the source code of css. But if include the map file in the page with bootstrap css file. you can see the less code which apply to the element style you want to inspect.