ERROR in bundle.js from UglifyJs Name expected

Question

I am trying to use UglifyJS to minimize/compress my bundle.js file. When I run webpack -p, I am getting the following:

ERROR in bundle.js from UglifyJs Name expected [bundle.js:105519,6]

Line 105519 is as follows:

const {M, l, pattern} = __webpack_require__(862).

I am using React w/ ES6. Any thoughts as to what is wrong?

I feel like I've seen this in gulp-land before, psure the solution was to transpile everything first then run uglify on the results of the transpile. — John Jones, Sep 05 '17 at 19:23

score 23 · Answer 1 · edited Sep 01 '17 at 22:45

Every version of Webpack has a built-in version of UglifyJS (0.4.6) which doesn't support ES6. This version supports ES5 syntax only.

There are two possible solutions:

Make transpiler target es5
Don't use the built-in version of uglifyjs-webpack-plugin and install the latest version using npm install -D uglifyjs-webpack-plugin. Add it to your plugins property in your configuration:
```
const UglifyJSPlugin = require('uglifyjs-webpack-plugin')

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

score 0 · Answer 2 · edited Jul 09 '19 at 20:48

This error comes when uglifyjs-webpack-plugin is not able to Uglify particular dependency

So, How to find library that creates such error ?

I was using react , so i deleted all forms in my app and kept just 1 form and imported all dependencies in it, and remove/add those dependencies one by one and run command

webpack -p

SO In My case it was browser-history creating such error .Now you can report this issue to that library's author with some replicating example

working Package.json & .babelrc

score 0 · Answer 3 · answered Sep 05 '17 at 13:06

Definitely an issue with the version of uglifyjs and the javascript target you are trying to compile to. It could be 2 things, your webpack setup and your babel setup causing this.

If you are using the latest version of webpack v3.5.5 it comes with uglifyjs-webpack-plugin ^0.4.6 which doesn't support a target of es6 or above.

Referring to the current Webpack docs about UglifyjsWebpackPlugin options it covers how to use the latest beta version of uglify-js-webpack-plugin v1.0.0-beta.2. But isnt that clear on how to install that version.

To use it with the Webpack do

yarn add uglifyjs-webpack-plugin@beta --dev

As you don't mention what your Babel setup is. You might be or want to use babel-preset-env as your preset. There is an option for uglifyjs.

Be great to see a repo or a Gist.

ERROR in bundle.js from UglifyJs Name expected

3 Answers3