vanilla JS : module bundled or not

Given a set of module-patterned files (a main one, and various subs),

is there a way to detect if modules are bundled together into one single file OR not ? In the last case, I will load manually modules with head script src="" tag added via JS.

Non-bundled files are for development, bundled one is for production use.

Code is ES 5 / 2015.

I don't consider using Browserify, Require or so on...

I assemble my code with (very basic) gulpfiles (using concat, wrap)

someone have an idea ?