How/where I can set eslint config file in spacemacs

Spacemacs (and flycheck, the autocompletion plugin that interfaces with eslint) don't look for eslint configs, they delegate that to eslint itself. If you're getting this issue it means eslint itself is erroring out when it tries to load your project config.

Run eslint --print-config . from your project directory and resolve all errors it prints out, and that should fix it.

I'm running a mac setup, this is what worked for me:

assuming you've installed eslint, you can enable syntax checking in your ~/.spacemacs file

---

Begin by typing SPC f e d and uncommenting syntax-checking

;; spell-checking
syntax-checking

• resync your config by typing SPC f e R
• open a javascript file in your project, which should have an .eslintrc in its root
• type SPC e v

From here you can confirm that javascript-eslint is enabled and that an .eslintrc has been detected for your project.