Webpack 3 bundle size is larger than Webpack 2.6.1

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
The build passes, but fails to concatenate, bundle size is bigger than with 2.6.1

ModuleConcatenation (inner): module is used with non-harmony imports from multi react-hot-loader/patch ./app.js
ModuleConcatenation: Cannot concat with ../node_modules/react-dom/index.js
ModuleConcatenation: Cannot concat with ../node_modules/react/react.js
ModuleConcatenation: Cannot concat with ./assets/styles/main.scss
ModuleConcatenation: Cannot concat with ../node_modules/cssrecipes-defaults/lib/box-sizing.css
ModuleConcatenation: Cannot concat with ../node_modules/cssrecipes-defaults/lib/document-remove-margin-padding.css
ModuleConcatenation: Cannot concat with ../node_modules/cssrecipes-defaults/lib/hidden.css
ModuleConcatenation: Cannot concat with ../node_modules/normalize.css/normalize.css

If the current behavior is a bug, please provide the steps to reproduce.
Tested on:
https://github.com/alexilyaev/react-es6-starter

See webpack3 branch:
alexilyaev/react-es6-starter#10

Run npm run build

What is the expected behavior?
I would expect the bundle size to at least stay the same…
And if I can figure out how to make ModuleConcatenationPlugin work, to be smaller.

Bundle size results:
Webpack 2.6.1: 268KB (67.3KB Gzip)
Webpack 3.0.0: 313KB (78.3KB Gzip)
Webpack 3.0.0: 317KB (78.6KB Gzip) (without ModuleConcatenationPlugin)

Please mention other relevant information such as the browser version, Node.js version, webpack version and Operating System.
macOS 10.12.5
Node 6.10.3
Everything else in package.json

Author: Fantashit

2 thoughts on “Webpack 3 bundle size is larger than Webpack 2.6.1

  1. I have the same issue and bigger bundle related to react-hot-loader,

    So, i checked that in my webpack.prod.config.js – there are no anything related to hot loader, the only one place where it used

    import { AppContainer as HotEnabler } from 'react-hot-loader'; in index.js file(root of project)

    And what i could see with webpack 2.2: everything is fine, bundle size 285 kb,
    With webpack 3(just changed version): 323kb,

    source-map-explorer telling me that with webpack 3, i have in the bundle

    react-hot-loader – 4 kb
    sourcemapped-stacktrace – 20 kb
    redbox-react – 10kb

    and it also telling me, that i do not have such libs in prod bundle with webpack 2

    Question, why after migration to webpack 3, react-hot-reload appeared in bundle? with webpack 2.x everything is fine

    @SidKwok @gaearon @aseem2625

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