Install Prettier

# Install a bunch of tools:
#
# eslint                 - looks for logical mistakes in the code (unused params etc), *not* formatting
# eslint-config-prettier - overrides default eslint rules to disable formatting rules
# eslint-plugin-prettier - configures `eslint --fix` to format code with prettier
# prettier               - prettifies code
# lint-staged            - only runs `eslint --fix` on files that have been staged with `git add`
# husky                  - automatically installs a precommit hook that runs lint-staged
#
yarn add --dev eslint eslint-config-prettier eslint-plugin-prettier prettier lint-staged husky

# Remove old eslint configuration
rm -f .eslintrc*

# Write new eslint configuration for modern JavaScrpt
cat > .eslintrc <<- ESLINTRC
{
  "parserOptions": {
    "ecmaVersion": 8
  },
  "plugins": [
    "prettier"
  ],
  "rules": {
    "prettier/prettier": [
      "error", {"trailingComma": "es5", "singleQuote": true, "semi": false}
    ]
  },
  "env": {
    "node": true,
    "es6": true
  },
  "extends": [
    "eslint:recommended",
    "prettier"
  ]
}
ESLINTRC


# Tell lint-staged to prettify all *.js files
# Change the value of the "gitDir" property if package.json is below the git repo root.
cat > .lintstagedrc << LINTSTAGEDRC
{
  "gitDir": ".",
  "linters": {
    "*.js": ["eslint --fix", "git add"]
  }
}
LINTSTAGEDRC

# Declare the precommit hook. Gets installed on yarn|npm install.
cat package.json | jq '.scripts.precommit = "lint-staged"' > package.json.tmp && mv package.json.tmp package.json

# Reformat all the files once before committing
./node_modules/.bin/eslint --fix **/*.js

# Fix your linting errors.
# You may have to add a header to your mocha tests:
# /* eslint-env mocha */
#

# You're done. From now on, only modified files get reformatted and linted.