is-webpack-bundle

1.0.0 verified Sat Apr 25 auth: no javascript maintenance

A micro-package (v1.0.0, no active releases since 2019) that detects at runtime whether the current module was bundled by webpack. It works by checking for the presence of a `__webpack_require__` function in the global scope. This is a simple, single-purpose utility with no dependencies. For similar detection in other bundlers (e.g., Rollup, Parcel), alternative approaches are needed. The package is published as a CommonJS module only, with no TypeScript type definitions.

Common errors

error Cannot find module 'is-webpack-bundle' ↓

cause Package not installed or typo in package name.

fix

Run npm install is-webpack-bundle

error Uncaught ReferenceError: __webpack_require__ is not defined ↓

cause The package's global check fails because __webpack_require__ is not exposed (e.g., in Node.js environment without webpack).

fix

This error should not happen because the package catches the ReferenceError internally; if it does, ensure you are not modifying global scope or using eval.

error SyntaxError: Cannot use import statement outside a module ↓

cause Trying to ESM-import the package without proper module configuration.

fix

Use require() or set "type": "module" in package.json and ensure the import path is valid.

Warnings

gotcha The check relies on a global `__webpack_require__` which may be absent in certain webpack configurations (e.g., output.libraryTarget: 'var') or minified bundles. ↓

fix Verify the check works in your specific webpack setup; consider alternative detection methods.

gotcha If the code is bundled with another bundler (e.g., Rollup, Parcel), the check will incorrectly return false even if inside a bundle. ↓

fix Use a bundler-agnostic detection library or check for other globals.

gotcha The module is CommonJS-only; importing via ESM may cause issues in strict ESM environments. ↓

fix Use require() or configure your bundler to handle CJS interop.

Install

npm install is-webpack-bundle

yarn add is-webpack-bundle

pnpm add is-webpack-bundle

Imports

default

wrong

import isWebpackBundle from 'is-webpack-bundle';

correct

const isWebpackBundle = require('is-webpack-bundle');

Package is CommonJS-only; ESM import will fail in Node or bundlers expecting ESM.

default (ESM)
wrong
```
const isWebpackBundle = require('is-webpack-bundle');
```
correct
```
import isWebpackBundle from 'is-webpack-bundle';
```
If your project is ESM, this import works in Node 12+ with `--experimental-require` or with bundlers like webpack, but the package itself is CJS. Prefer require for clarity.

default (TypeScript)

wrong

import isWebpackBundle from 'is-webpack-bundle';

correct

// @ts-ignore or declare module
const isWebpackBundle = require('is-webpack-bundle');

No type definitions exist. Use require with a type assertion or disable strict module checks.

Quickstart

Shows how to check if code is webpack-bundled and conditionally handle logic.

const isWebpackBundle = require('is-webpack-bundle');

if (isWebpackBundle) {
  console.log('Running inside a webpack bundle');
} else {
  console.log('Not bundled by webpack');
}

// Example usage: conditionally handle module exports
const myModule = isWebpackBundle
  ? { bundled: true }
  : { bundled: false };

module.exports = myModule;