Webpack的UglifyJsPlugin对包含let的Node模块抛出错误

Question

This is the relevant code (I'm using Vue.js' Webpack official template):

.babelrc:

"presets": [
  "babel-preset-es2015",
  "babel-preset-stage-2",
]

webpack.prod.config.js

new webpack.optimize.UglifyJsPlugin({
  compress: {
    warnings: false,
    drop_console: shouldDropConsole
  },
  sourceMap: true
}),

This is the error I get when I do npm run build :

ERROR in static/js/vendor.a6271913414e87e123c2.js from UglifyJs Unexpected token: name (_months) [./node_modules/calendar-js/index.js:56,0][static/js/vendor.a6271913414e87e123c2.js:90602,6]

This is the offending line:

let _months = MONTHS;

(If I replace all the let 's to var s the project is built without problems. And the const 's don't seem to bother Webpack/UglifyJS.)

Do I need to configure something so that Webpack/UglifyJS build node modules containing let 's? (The let 's in my actual project don't give me problems.)

Answer 1

This could be because you might be using an older version of node which does not support es6 syntax.

let , const , arrow functions etc. are part of es6 syntax. To know more follow this link http://es6-features.org/

You might need the older version of node for your other projects so install nvm. NVM is a node version manager which will help you to switch between node versions easily. Follow the link for documentation and installation process https://github.com/creationix/nvm

Node v6+ supports ES6 syntax try upgrading to that.

UPDATE

On the comments of this answer, it's confirmed that it was not a version issue and got resolved by following this GitHub issue thread https://github.com/joeeames/WebpackFundamentalsCourse/issues/3 .

Peace!