How to run POSTCSS AFTER sass-loader and ExtractTextPlugin have finished?

Question

I am trying to figure out how to run postcss on my final output css file.

'strict';

const path = require('path');
const webpack = require('webpack');
const StatsPlugin = require('stats-webpack-plugin');

/* POSTCSS Optimizations of CSS files */
const clean = require('postcss-clean');
const colorMin = require('postcss-colormin');
const discardDuplicates = require('postcss-discard-duplicates');
const discardEmpty = require('postcss-discard-empty');
const mergeRules = require('postcss-merge-rules');
const mergeLonghand = require('postcss-merge-longhand');
const minifyFonts = require('postcss-minify-font-values');
const orderedValues = require('postcss-ordered-values');
const uniqueSelectors = require('postcss-unique-selectors');

/* EXTRACT CSS for optimization and parallel loading */
const ExtractTextPlugin = require('extract-text-webpack-plugin');

module.exports = {
    entry: './src/index',
    output: {
        path: path.join(__dirname, 'dist'),
        filename: '[name].js',
        chunkFilename: '[id].bundle.js',
        publicPath: '/dist/',
        soureMapFilename: '[file].map'
    },
    plugins: [
        new webpack.optimize.OccurenceOrderPlugin(),
        new webpack.NoErrorsPlugin(),
        new StatsPlugin('stats.json'),
        new ExtractTextPlugin('assets/css/[name].css?[hash]-[chunkhash]-[contenthash]-[name]', {
            disable: false,
            allChunks: true
        })
    ],
    node: {
        net: 'empty',
        tls: 'empty',
        dns: 'empty'
    },
    module: {
        loaders: [{
            test: /\.js$/,
            loaders: ['babel'],
            exclude: /node_modules/,
            include: __dirname
        },
        {
            test: /\.scss$/i,
            loader: ExtractTextPlugin.extract('style', ['css', 'postcss', 'sass'])
        },
        {
            test: /\.css$/,
            loader: ExtractTextPlugin.extract('style', ['css'])
        },
        {
            test: /\.(eot|woff|woff2|ttf|svg|png|jpg)$/,
            loader: 'url-loader?limit=30000&name=[name]-[hash].[ext]'
        }]
    },
    postcss() {
        return [mergeRules, mergeLonghand, colorMin, clean, discardEmpty,
                orderedValues, minifyFonts, uniqueSelectors, discardDuplicates];
    },
    sassLoader: {
        includePaths: [path.resolve(__dirname, './node_modules')]
    }
};

My current configuration works well at compiling all of the dependent SASS and taking that and the static CSS imports and extracting them using ExtractTextPlugin.

It also appears that I can run POSTCSS optimizations on chunks of the CSS, but not the final product. This means I can't get rid of duplicate CSS rules.

How do I run POSTCSS on the end-state CSS file AFTER sass-loader and extractTextPlugin have worked their magic?

Answer 1

I was having problems to make a similar setup work with ExtractTextPlugin and my problem was on how I was using the ExtractTextPlugin plugin.

I'm only using it for production builds and this is what worked for me:

module: {
    loaders: [
        {   // styles
            test: /\.scss$/,
            include: [ path.join(__dirname, 'source/styles') ],
            loader: ExtractTextPlugin.extract('style', ['css', 'postcss', 'sass'])
        }
    ]
},

Note the Array for ['css', 'postcss', 'sass']. That's the part that I was missing. This array will resolve first and then run style that will be finally extracted by the plugin.

And, on the array of plugins I'm using new ExtractTextPlugin('styles-[chunkhash].css').