Simple plugin only for one simple rule, don't use toUpperCase but use toLocaleUpperCase

Install ESLint either locally or globally.

$ npm install eslint
$ npm install eslint-plugin-no-touppercase

Add plugins section and specify ESLint-plugin-React (optional) and ESLint-plugin-react-native as a plugin.

{
  "plugins": [
    "no-touppercase"
  ]
}

Enable all of the rules that you would like to use.

{
  "rules": {
    "no-touppercase/check-uppercase": 2,
  }
}