Add the Webpack 4 'sideEffects' flag

[jsnajdr]

This adds the Webpack v4 sideEffects optimization. See a similar PR for Lodash: lodash/lodash#3533

What does it do? If I import just one export from the library:

import { reducer } from 'redux-form'

then sideEffects: false ensures that only the reducer code and the code it depends on will be imported, and not all the reexports in es/index.js.

If the sideEffects flag were not set to false, Webpack must assume that the reexported modules can have side-effects (e.g., setting a property on window) and imports them all.

Very useful for code splitting where the main chunk typically imports only the reducer and the other chunks import UI components, selectors etc.

[codecov-io]

Codecov Report

Merging #3870 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #3870   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files          70      70           
  Lines        1601    1601           
======================================
  Hits         1601    1601

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[erikras]

Published in v7.3.0.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.