What is the proper syntax for adding JS to _main.js?

I can’t get my _main.js working at all, it just throws errors in grunt watch all the time.
I updated the .jshintrc file, but that doesn’t change anything unfortunately.

Doesn’t even matter what I change in the _main.js, it just gives me errors about every plugin I placed in the plugins folder, while these errors don’t occur when building with grunt:

Running "jshint:all" (jshint) task
Linting assets/js/plugins/fresco.js ...ERROR
[L9:C70] W065: Missing radix parameter.
Linting assets/js/plugins/jquery.fitmaps.js ...ERROR
[L34:C10] W033: Missing semicolon.
Linting assets/js/plugins/jquery.fitvids.js ...ERROR
[L2:C1] E002: Bad option value.

etc…

Any ideas?