Why inline source maps?

Question

Today I learned that it is possible to include source maps directly into your minified JavaScript file instead of having them in a separate example.min.map file. I wonder: why would anybody want to do something like that?

The benefit of having source maps is clear to me: one can for example debug errors with the original, non-compressed source files while running the minified files. The benefit of minimization is also clear: the size of source files is greatly reduced, making it quicker for browsers to download.

So why on Earth I would want to include the source maps into the minified file, given that the maps have size even greater than the minified code itself?

Answer 1

I searched around and the only reason I could see that people inline source maps is for use in development. Inlined source maps should not be used in production.

The rational for inlining the source maps with your minified files is that the browser is parsing the exact same JavaScript in development and production. Some minifiers like Closure Compiler do more than 'just' minify the code. Using the advanced options it can also do things like: dead code removal, function inlining, or aggressive variable renaming. This makes the minified code (potentially) functionally different than the source file.

This could still be done by referencing external source map files of course, but some people seem to prefer inlining for their build process.

Answer 2

If you are remote debugging Chrome on an android device, the Chrome debugger cannot just access any file it wants on the device and that includes separate map files. If you include them inline you don't have this issue.

Answer 3

JS bundling tools like Browserify or Webpack will bundle all your .js files input one or several bundles, even in developing mode. So in this case, adding inline source map to generated bundles is the easiest way to help debugging without bringing extra files.