Given you’re using module logger:

// src/index.js
const logger = require('./logger');
logger('hi');

Your bundle is built using the webpack config:

// webpack.config.js
module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'main.js',
  },
};

When you build the bundle, how can logger be removed?

NODE_ENV=development npx webpack
asset main.js 2.46 KiB [emitted] (name: main)
./src/index.js 50 bytes [built] [code generated]
./src/logger.js 30 bytes [built] [code generated]
webpack 5.37.0 compiled successfully in 67 ms

IgnorePlugin

With IgnorePlugin, a regular expression can be tested to prevent the module from being generated:

 // webpack.config.js
+const { IgnorePlugin } = require('webpack');
 
 module.exports = {
   entry: './src/index.js',
   output: {
     filename: 'bundle.js',
   },
+  plugins: [
+    new IgnorePlugin({
+      resourceRegExp: /logger/,
+    }),
+  ],
 };

When you build the bundle, notice how logger is no longer part of the generated code:

webpack-dev-serverNODE_ENV=development npx webpack
asset main.js 2.33 KiB [emitted] (name: main)
./src/index.js 50 bytes [built] [code generated]
webpack 5.37.0 compiled successfully in 61 ms

But when you open your webpage:

<!-- index.html -->
<script src="dist/main.js"></script>

The Console will show a JavaScript error:

Uncaught Error: Cannot find module './logger'
    at webpackMissingModule (index.js:1)
    at eval (index.js:1)
    at Object../src/index.js (main.js:18)
    at __webpack_require__ (main.js:42)
    at main.js:53
    at main.js:55

This is because logger is still required in src/index.js.

DefinePlugin

To have webpack prune unused code, use DefinePlugin:

 // webpack.config.js
-const { IgnorePlugin } = require('webpack');
+const { DefinePlugin, IgnorePlugin } = require('webpack');
 
+const { NODE_ENV } = process.env;
 
 module.exports = {
   entry: './src/index.js',
   output: {
     filename: 'main.js',
   },
   plugins: [
-    new IgnorePlugin({
-      resourceRegExp: /logger/,
-    }),
+   NODE_ENV === 'production' &&
+     new IgnorePlugin({
+       resourceRegExp: /logger/,
+     }),
+    new DefinePlugin({
+      'process.env.NODE_ENV': JSON.stringify(NODE_ENV),
+    }),
   ],
 };

The plugin allows you to create global constants that are injected at compile time:

// src/index.js
if (process.env.NODE_ENV === 'development') {
  const logger = require('./logger');
  logger('hi');
}

Build the bundle:

NODE_ENV=production npx webpack
asset main.js 0 bytes [emitted] [minimized] (name: main)
./src/index.js 102 bytes [built] [code generated]
webpack 5.37.0 compiled successfully in 134 ms

Open the webpage to see no Console errors.

open index.html

To learn more about Webpack global constants, check out the following post.