Global variables in Javascript and ESLint

I have got multiple javascript files and I have defined some global variable in a file which loads before the others.
As a consequence all of the files loaded after the first have access to the global variable.
However ESLint shows the global variable as "not defined". I don't want to change the rules of ESLint and I would like to find an elegant way to get rid of these error messages.
Any clue?
Thanks