Error during Minification

[knlgpt]

Hi
I m trying to compile a bunch of separate js file in one file using "prepros".

Without Minification
But when I m attaching validator js browser gives me an error message in the console "Uncaught SyntaxError: Unexpected token !"

With Minification
When I m trying to minify using prepos it does not compile and prepros gives an error
"Unexpected token: operator (!)"