UglifyJS Webpack Plugin

2.2.0 verified Sat Apr 25 auth: no javascript maintenance

UglifyJS Webpack Plugin uses UglifyJS (v2) to minify JavaScript bundles generated by webpack. The latest stable version is 2.2.0, released July 2019, supporting webpack 4+ and Node 6.9+. It offers caching, parallelization, source maps, and advanced options like chunk filtering. However, it is now largely superseded by terser-webpack-plugin, which supports ES6+ and is the recommended minimizer for webpack 4+. This plugin switched back from uglify-es to uglify-js in v2.0.0, meaning it does not handle modern JavaScript (ES6+) out of the box. It is in maintenance mode with no active development.

Common errors

error Error: Plugin could not be used because optimization.minimizer is not an array. ↓

cause Plugin is placed directly in plugins array instead of optimization.minimizer.

fix

Move the plugin instance to optimization: { minimizer: [new UglifyJsPlugin()] }.

error TypeError: Cannot read property 'call' of undefined ↓

cause Incorrect import or missing 'new' keyword when instantiating plugin.

fix

Use: const UglifyJsPlugin = require('uglifyjs-webpack-plugin'); new UglifyJsPlugin();

error Error: uglify-js@3.x is not compatible with this plugin. ↓

cause Package depends on uglify-js v2, but uglify-js v3 is installed.

fix

Ensure uglify-js version 2.x is installed (npm install uglify-js@2).

error UglifyJsPlugin: parallel option not supported in single-threaded mode ↓

cause Setting parallel: true on platforms with a single CPU or where worker farm fails.

fix

Set parallel: false or ensure worker-farm is properly installed.

Warnings

breaking uglify-es has been abandoned; uglifyjs-webpack-plugin switched back to uglify-js in v2.0.0. ↓

fix For ES6+ support, migrate to terser-webpack-plugin.

deprecated This plugin is in maintenance mode; no new features are being added. ↓

fix Use terser-webpack-plugin for active development and ES6+ minification.

gotcha Parallelization may fail on Windows Subsystem for Linux (WSL); disable with parallel: false. ↓

fix Set parallel: false in plugin options.

gotcha Default cache directory is node_modules/.cache/uglifyjs-webpack-plugin; may cause issues in CI environments. ↓

fix Set cache to a custom path or disable cache in CI.

gotcha Plugin options must be placed under webpack optimization.minimizer, not under plugins. ↓

fix Use optimization: { minimizer: [new UglifyJsPlugin()] } in webpack config.

breaking Default extract comment condition is case insensitive, may produce different results than v1. ↓

fix Explicitly set extractComments option to control comment extraction.

Install

npm install uglifyjs-webpack-plugin

yarn add uglifyjs-webpack-plugin

pnpm add uglifyjs-webpack-plugin

Imports

UglifyJsPlugin

wrong

import UglifyJsPlugin from 'uglifyjs-webpack-plugin';

correct

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

This package provides a CommonJS default export; ESM import may fail in some bundlers.

UglifyJsPlugin

wrong

import { UglifyJsPlugin } from 'uglifyjs-webpack-plugin';

correct

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

Named import is incorrect; the plugin is exported as a single default.

default
```
import UglifyJsPlugin from 'uglifyjs-webpack-plugin';
```
If using ESM, use default import, but ensure your environment supports it. CJS require() is safer.

Quickstart

Configures webpack to use UglifyJS plugin with caching, parallelization, source maps, and options to remove console logs and comments.

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

module.exports = {
  mode: 'production',
  optimization: {
    minimizer: [
      new UglifyJsPlugin({
        cache: true,
        parallel: true,
        sourceMap: true,
        uglifyOptions: {
          compress: {
            drop_console: true,
          },
          output: {
            comments: false,
          },
        },
      }),
    ],
  },
};