verify_uglifyjs_error

function verify_uglifyjs_error {
  # Create stub dependency
  echo "module.exports = class {}" >> node_modules/es6-sample.js
  # Save App.js, we're going to modify it
  cp src/App.js src/App.js.bak

  # Add an es6 dependency
  echo "import es6 from 'es6-sample'" | cat - src/App.js > src/App.js.temp && mv src/App.js.temp src/App.js

  if `npm run build` | grep -xqFe "Failed to minify the code from this file: 

 ./~/es6-sample.js line 1:0 

Read more here: http://bit.ly/2tRViJ9" 
  then
    echo "matched"
  else
    exit 1
  fi
  # Restore App.js
  rm src/App.js
  mv src/App.js.bak src/App.js
}