.babelrc

{
  "presets": [
    ["env", {
      "modules": false,
      "targets": {
        "browsers": ["> 1%", "last 2 versions", "not ie <= 8"]
      }
    }],
    "stage-2"
  ],
  "plugins": ["transform-runtime"],
  "env": {
    "test": {
      "presets": ["env", "stage-2"],
      "plugins": ["istanbul"]
    }
  }
}

error.log

ERROR in static/js/5.93ab66d4a749cd072641.js from UglifyJs
Unexpected token: name (resolvePromise) [./node_modules/vue-charts/src/utils/makeDeferred.js:6,0][static/js/5.93ab66d4a749cd072641.js:20667,6]

ERROR in static/js/6.607ca16377a1e18dc831.js from UglifyJs
Unexpected token: name (resolvePromise) [./node_modules/vue-charts/src/utils/makeDeferred.js:6,0][static/js/6.607ca16377a1e18dc831.js:20638,6]

makeDeferred.js

/*
    This lets us resolve the promise outside the
    promise function itself.
 */
export function makeDeferred () {
  let resolvePromise = null
  let rejectPromise = null

  let promise = new Promise((resolve, reject) => {
    resolvePromise = resolve
    rejectPromise = reject
  })

  return {
    promise: promise,
    resolve: resolvePromise,
    reject: rejectPromise
  }
}

export default makeDeferred

webpack.config.js

// ...
    new webpack.optimize.UglifyJsPlugin({
      compress: {
        warnings: false
      },
      sourceMap: true,
      uglifyOptions: {
        ie8: false,
        ecma: 7
      }
    })
// ...