Unexpected token: operator (>) from UglifyJs

Question

I have 2 Vue-Cli webpack projects (ClientApp and Lib). Lib is my components library (shared with other projects)

Problem

When I build my project ClientApp npm run build, I have the following error:

ERROR in static/js/app.d08a24ce0e8d0438ce68.js from UglifyJs
Unexpected token: operator (>) [C:/.../Lib/src/tools/escape-key.js:3,0][static/js/app.d08a24ce0e8d0438ce68.js:17468,38]

Questions

It seems like the error comes from an arrow function in the file escape-key.js. This is ES6 syntax and UglifyJS can't parse this. Shouldn't Babel go first, before Uglify? Note that is works well with *.vue files.

Project structure

ClientApp
   | - build
   | - config
   | - src
       | - App.Vue // import EscapeKey from '~lib/tools/escape-key';



Lib
  | -src
     | - tools
         | - escape-key.js

ClientApp's webpack.base.conf.js file

Note there is an alias to Lib.

resolve: {
    extensions: ['.js', '.vue', '.json'],
    alias: {
      '@': resolve('src'),
      '~lib': path.join(__dirname, '../../lib/src'),
    }
  },

Please feel free to ask for more details if required.

Answer 1

This solved the problem for me. I installed uglifyjs-webpack-plugin

npm install uglifyjs-webpack-plugin --save-dev

Then added this to my webpack.config

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

module.exports = {
  plugins: [
    new UglifyJSPlugin()
  ]
}

Answer 2

The version of uglify that you are using probably doesn't support ES6.

https://github.com/mishoo/UglifyJS2/tree/harmony is the es6 version as of now

if you want to use the webpack plugin, make sure to pay attention to the install section regarding es6

Important! The plugin has a peer dependency to uglify-js, so in order to use the plugin, also uglify-js has to be installed. The currently (2017/1/25) available uglify-js npm packages; however, do not support minification of ES6 code. In order to support ES6, an ES6-capable, a.k.a. harmony, version of UglifyJS has to be provided.

If your minification target is ES6:

yarn add git://github.com/mishoo/UglifyJS2#harmony-v2.8.22 --dev

Answer 3

After changing my babel-loader config, it worked.

Babel-loader config

{
  test: /\.js$/,
  loader: 'babel-loader',
  include: [path.join(__dirname, '../../Lib/src'), resolve('src'), resolve('test')]
}

Answer 4

Add

"uglifyjs-webpack-plugin": "v1.0.0-beta.1",

to your dev dependencies and update your webpack.config.js file to use this version explicitly:

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

module.exports = {
  plugins: [
    new UglifyJSPlugin()
  ]
}

uglifyjs-webpack-plugin latest stable release (v0.4.6) uses older version of uglify-js instead of uglify-es that is capable of transpiling ES6. This dependency was updated in 1.0.0-beta.1 release.

https://github.com/webpack-contrib/uglifyjs-webpack-plugin/releases/tag/v1.0.0-beta.1