You add 'hello' in the linter's config as a pre-defined global, until you get around to fixing that.

I would not want my linter to load multiple files, since that pattern of polluting the global namespace is really not maintainable.

The fix can be fairly simple if you wrap your entire b.js file in a function that takes an argument of 'hello' which you invoke from a.js.

If that doesn't work because you have too many global declarations you should probably just dump all the code into one giant file.

That might seem terrible and unmaintainable, but it is exactly what you already have.

Once the mess is all in one spot you can use a linter to start improving the quality, and begin breaking of the code into actual modules.