postcss with webpack

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const ExtractTextPlugin = require('extract-text-webpack-plugin');
const cssExtractPlugin = new ExtractTextPlugin('/css/[name]_[contenthash].css');

var autoprefixer = require('autoprefixer');
var precss = require('precss');

const conf = {
    entry: {
        'main': ['./assets/js/main.js']
    },

    output: {
        hash: true,
        path: path.join(__dirname, 'output'),
        publicPath: '',
        filename: '/js/[name]_[hash].js',
        chunkFilename: '/js/chunk_[id]_[chunkhash].js'
    },

    module: {
        loaders: [
            {
                test: /\.css$/,
                loader: cssExtractPlugin.extract("style-loader", "css-loader!postcss-loader")
            }
        ]
    },

    postcss: function () {
        return [
            autoprefixer,
            precss
        ];
    },

    plugins: [
        cssExtractPlugin,
        new HtmlWebpackPlugin({
            template: 'index.html',
            filename: 'index.html',
            inject: 'body',
            chunks: ['main']
        })
    ],

    devServer: {
        port: '9999'
    }
};

module.exports = conf;