Run eslint before `git commit` with npm scripts and `pre-commit` package.

pre-commit-lint.json

{
  "scripts": {
    "lint-legacy": "files=$(git diff --cached --name-only | grep -v '.jsx$' | grep '.js$' | tr '\\n' ' ');  if [[ -n \"$files\" ]]; then eslint --config ./.eslintrc.legacy.json --quiet $files || (git reset HEAD; exit 1); else exit 0; fi",
    "lint-base": "files=$(git diff --cached --name-only | grep '.jsx$' | tr '\\n' ' ');  if [[ -n \"$files\" ]]; then eslint --config ./.eslintrc.base.json --quiet $files || (git reset HEAD; exit 1); else exit 0; fi",
    "lint": "npm run lint-legacy && npm run lint-base",
    "lint-all": "(eslint --config ./.eslintrc.base.json --ext .jsx --quiet ./) && (eslint --config ./.eslintrc.legacy.json --ext .js --quiet ./)",
    "build": "gulp build"
  },
  "pre-commit": [
    "lint"
  ],

}