Format staged files with Prettier before commit

formatStagedFiles.sh

#!/bin/bash

STAGED=$(git diff --name-only --cached --diff-filter=AM | egrep '^(.*).(js|json|css)$')

yarn prettier --write $STAGED
git add $STAGED

package.json

{
  "name": "my-app",
  "version": "0.1.0",
  "dependencies": {},
  "devDependencies": {
    "pre-commit": "^1.2.2",
    "prettier": "^1.10.2"
  },
  "scripts": {
    "format-staged": "bash scripts/formatStagedFiles.sh"
  },
  "pre-commit": ["lint", "format-staged", "test"]
}