CopyWebpackPlugin

npm install --save-dev copy-webpack-plugin

var CopyWebpackPlugin = require('copy-webpack-plugin');
var path = require('path');

module.exports = {
    context: path.join(__dirname, 'app'),
    devServer: {
        // This is required for older versions of webpack-dev-server
        // if you use absolute 'to' paths. The path should be an
        // absolute path to your build destination.
        outputPath: path.join(__dirname, 'build')
    },
    plugins: [
        new CopyWebpackPlugin([
            // {output}/file.txt
            { from: 'from/file.txt' },

            // equivalent
            'from/file.txt',

            // {output}/to/file.txt
            { from: 'from/file.txt', to: 'to/file.txt' },

            // {output}/to/directory/file.txt
            { from: 'from/file.txt', to: 'to/directory' },

            // Copy directory contents to {output}/
            { from: 'from/directory' },

            // Copy directory contents to {output}/to/directory/
            { from: 'from/directory', to: 'to/directory' },

            // Copy glob results to /absolute/path/
            { from: 'from/directory/**/*', to: '/absolute/path' },

            // Copy glob results (with dot files) to /absolute/path/
            {
                from: {
                    glob:'from/directory/**/*',
                    dot: true
                },
                to: '/absolute/path'
            },

            // Copy glob results, relative to context
            {
                context: 'from/directory',
                from: '**/*',
                to: '/absolute/path'
            },

            // {output}/file/without/extension
            {
                from: 'path/to/file.txt',
                to: 'file/without/extension',
                toType: 'file'
            },

            // {output}/directory/with/extension.ext/file.txt
            {
                from: 'path/to/file.txt',
                to: 'directory/with/extension.ext',
                toType: 'dir'
            }
        ], {
            ignore: [
                // Doesn't copy any files with a txt extension    
                '*.txt',

                // Doesn't copy any file, even if they start with a dot
                '**/*',

                // Doesn't copy any file, except if they start with a dot
                { glob: '**/*', dot: false }
            ],

            // By default, we only copy modified files during
            // a watch or webpack-dev-server build. Setting this
            // to `true` copies all files.
            copyUnmodified: true
        })
    ]
};

var fs = require('fs');
var gracefulFs = require('graceful-fs');
gracefulFs.gracefulify(fs);