cssnano/cssnano v4.0.0-rc.0

on GitHub

Since version 4 has been in-development for some time, we thought it would be
best to release an alpha version so that we could catch any issues before
the actual release.

Breaking changes

• cssnano & its plugins have been upgraded to PostCSS 6.x. Please ensure that
  for optimal results that you use cssnano with a PostCSS 6 compatible runner
  & that any other plugins are also using PostCSS 6.

• cssnano is now essentially a preset loader and does not contain any built-in
  transforms (instead, it delegates to cssnano-preset-default by default).
  Due to the new architecture, it's not possible to exclude asynchronous
  transforms and run it synchronously, unlike in 3.x. Any transforms that
  were "core" modules have now been extracted out into separate packages.

• Because of the new preset system, cssnano will not accept any transformation
  options; these must be set in the preset. The option names remain mostly the
  same, except some cases where "core" modules have been extracted out:

  • core is now normalizeWhitespace.
  • reduceBackgroundRepeat is now normalizeRepeatStyle.
  • reduceDisplayValues is now normalizeDisplayValues.
  • reducePositions is now normalizePositions.
  • reduceTimingFunctions is now normalizeTimingFunctions.
  • styleCache is now rawCache.

  When excluding transforms, we now have an exclude option (in 3.x this was
  named disable). Similarly, the safe option was removed; the defaults
  are now much less aggressive.

• By default, the following transforms are no longer applied to any input CSS.
  You may see an increased output file size as a result:

  • autoprefixer
  • postcss-discard-unused
  • postcss-merge-idents
  • postcss-reduce-idents
  • postcss-zindex

  Note that you can load cssnano-preset-advanced instead which does contain
  these transforms.

• We no longer detect previous plugins to silently exclude our own, and now
  consider this to be an anti-pattern. So postcss-filter-plugins was removed.

• We also changed some options to make the default transforms safer:

  • postcss-minify-font-values: removeAfterKeyword set to false from true.
  • postcss-normalize-url: stripWWW set to false from true.

• cssnano now does not accept the sourcemap shortcut option; please refer
  to the PostCSS documentation on sourcemaps. The quickstart.js file included
  with this module will give you a good starting point.

• cssnano.process is no longer a custom method; we use the built-in process
  method exposed on each PostCSS plugin. The new signature is
  cssnano.process(css, postcssOpts, cssnanoOpts), in 3.x it was
  cssnano.process(css, cssnanoOpts).

• We dropped support for Node 0.12, now requiring at least Node 4.

• Finally, cssnano is now developed as a monorepo, due to the fact that some
  transforms have a lot of grey area/overlap. Due to this, some modules have
  been refactored to delegate responsibility to others, such that duplication
  of functionality is minimized. For instance, postcss-colormin will no
  longer compress whitespace or compress numbers, as those are handled by
  postcss-normalize-whitespace & postcss-convert-values respectively.

Other changes

• Due to the PostCSS 6 upgrade, we have been able to reduce usage of custom
  methods, such as node clone behaviour. In cases where some utility
  has been used by several plugins it is now a separate package, reducing
  cssnano's footprint.
• cssnano now makes much better use of Browserslist. postcss-colormin &
  postcss-reduce-initial were enhanced with different behaviour depending
  on which browsers are passed. And now, the footprint for the caniuse-db
  dependency is much smaller thanks to caniuse-lite - 7 times smaller as
  of this writing. This makes cssnano much faster to download from npm!