"npm run build" results in error in UglifyJS

[leonardojobim]

Executing the command "npm run build" is resulting in error in UglifyJS.
It isn't able to recognize keys words like "let" and "new" and is showing error messages like below:

ERROR in build.js from UglifyJs Unexpected token: punc (() [build.js:11307,24]
ERROR in build.js from UglifyJs Unexpected token: name (app)

[AlexisSniffer]

solve it like this

const UglifyJsPlugin = require('uglifyjs-webpack-plugin')


if (process.env.NODE_ENV === 'production') {
  module.exports.devtool = '#source-map'
  // http://vue-loader.vuejs.org/en/workflow/production.html
  module.exports.plugins = (module.exports.plugins || []).concat([
    new webpack.DefinePlugin({
      'process.env': {
        NODE_ENV: '"production"'
      }
    }),
    new UglifyJsPlugin({
      uglifyOptions: {        
        ecma: 8      
      }
    }),
    new webpack.LoaderOptionsPlugin({
      minimize: true
    })
  ])
}

[leonardojobim]

I recreated the project and it worked fine.
Thank you.