Package Exports

universal-webpack
universal-webpack/build/chunks plugin
universal-webpack/build/server configuration

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (universal-webpack) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

universal-webpack

Helps setting up isomorphic (universal) Webpack build: the one that's working both on client and server.

Motivation

In summer 2015 I wrote webpack-isomorphic-tools as an experiment to make isomorphic (universal) React rendering work on server-side when the project was built with Webpack. At that time I barely knew how that "Webpack" thing worked so I ended up actually reimplementing some of the Webpack functionality on the server-side.

Still, the goal was met, the whole thing worked, and many people started using webpack-isomorphic-tools in their apps to implement isomorphic (universal) rendering.

But while webpack-isomorphic-tools supports the core Webpack functionality (resolve.aliases and such) it still lacks some Webpack features like various plugins and other advanced stuff.

So I did some research on Webpack builds for Node.js and came up with this proof-of-concept solution which seems to work good enough. It supports all Webpack features (all plugins, etc).

Installation

npm install universal-webpack --save
npm install extract-text-webpack-plugin --save

Example project

You may refer to this sample project as an example of using this library (see webpack directory, package.json and code/page-server/web server.js).

Usage

Suppose you have a typical webpack.config.js file. Create two new files called webpack.config.client.js and webpack.config.server.js with the following contents:

webpack.config.client.js

import { client_configuration } from 'universal-webpack'
import settings from './universal-webpack-settings'
import configuration from './webpack.config'

export default client_configuration(configuration, settings)

webpack.config.server.js

import { server_configuration } from 'universal-webpack'
import settings from './universal-webpack-settings'
import configuration from './webpack.config'

export default server_configuration(configuration, settings)

universal-webpack-settings.js

export default
{
    server:
    {
        input: './source/server.js',
        output: './build/server/server.js'
    }
}

Use webpack.config.client.js instead of the old webpack.config.js for client side Webpack builds.

The server_configuration() function takes the client-side Webpack configuration and tunes it a bit for server-side usage (target: "node").

The server-side bundle (settings.server.output file) is generated from settings.server.input file by Webpack when it's run with the webpack.config.server.js configuration. An example of settings.server.input file may look like this (it must export a function):

source/server.js

// express.js
import path from 'path'
import http from 'http'
import express from 'express'
import http_proxy from 'http-proxy'

// react-router
import routes from '../client/routes.js'

// Redux
import store from '../client/store.js'

// The server code must export a function
// (`parameters` may contain some miscellaneous library-specific stuff)
export default function(parameters)
{
    // Create HTTP server
    const app = new express()
    const server = new http.Server(app)

    // Serve static files
    app.use(express.static(path.join(__dirname, '..', 'build/assets')))

    // Proxy API calls to API server
    const proxy = http_proxy.createProxyServer({ target: 'http://localhost:xxxx' })
    app.use('/api', (req, res) => proxy.web(req, res))

    // React application rendering
    app.use((req, res) =>
    {
        // Match current URL to the corresponding React page
        // (can use `react-router`, `redux-router`, `react-router-redux`, etc)
        react_router_match_url(routes, req.originalUrl).then((error, result) =>
        {
            if (error)
            {
                res.status(500)
                return res.send('Server error')
            }
        
            // Render React page

            const page = redux.provide(result, store)

            res.status(200)
            res.send('<!doctype html>' + '\n' + ReactDOM.renderToString(<Html>{page}</Html>))
        })
    })

    // Start the HTTP server
    server.listen()
}

The last thing to do is to create a startup file for the server side. This is the file you're gonna run with Node.js, not the file provided above.

source/start-server.js

import { server } from 'universal-webpack'
import settings from '../universal-webpack-settings'
import configuration from '../webpack.config'

server(configuration, settings)

Calling source/start-server.js will basically call the function exported from source/server.js built with Webpack.

In the end you run all the above things like this (in parallel):

webpack-dev-server --hot --inline --config "./webpack.config.client.js --port XXXX --colors --display-error-details"

webpack --watch --config "./webpack.config.server.js" --colors --display-error-details

nodemon "./source/start-server" --watch "./build/server"

The above three commands are for development mode. For production mode the single command will be:

webpack --config "./webpack.config.client.js" --colors --display-error-details
webpack --config "./webpack.config.server.js" --colors --display-error-details
node "./source/start-server"

Chunks

This library will pass the chunks() function parameter (inside the parameters argument of the server-side function) which returns webpack-compiled chunks filename info:

build/webpack-chunks.json

{
    javascript:
    {
        main: `/assets/main.785f110e7775ec8322cf.js`
    },

    styles:
    {
        main: `/assets/main.785f110e7775ec8322cf.css`
    }
}

These filenames are required for <script src=.../> and <link rel="style" href=.../> tags in case of isomorphic (universal) rendering on the server-side.

Drawbacks

It will output double the amount of all assets included in the project: one complete bundle for client-side build and one complete bundle for server-side build. E.g. an asset ./images/dog.jpg will be output both into ./build/client/9059f094ddb49c2b0fa6a254a6ebf2ad.jpg and ./build/server/9059f094ddb49c2b0fa6a254a6ebf2ad.jpg. If you find a way to avoid that, drop me a line.

Also, it will perform two Webpack builds instead of one, but this shouldn't be much of an issue since developers' machines are highly multicore these days.

Advanced configuration

{
    // By default, all `node_modules` are marked as `external`
    // for server-side Webpack build.
    //
    // With this setting one can explicitly define which modules 
    // aren't gonna be marked as `external` dependencies.
    // (and therefore are gonna be compiled with `babel-loader` by Webpack)
    //
    // Can be used for ES6-only `node_modules`.
    // A more intelligent solution would be accepted:
    // https://github.com/halt-hammerzeit/universal-webpack/issues/10
    //
    exclude_from_externals:
    [
        'lodash-es',
        /^some-other-es6-only-module(\/.*)?$/
    ]
}

Source maps

I managed to get source maps working in my Node.js server-side code using source-map-support module.

source/start-server.js

// Enables proper source map support in Node.js
import 'source-map-support/register'

// The rest is the same as in the above example

import { server } from 'universal-webpack'
import settings from '../universal-webpack-settings'
import configuration from '../webpack.config'

server(configuration, settings)

Without source-map-support enabled it would give me No element indexed by XXX error (which means that by default Node.js thinks there are references to other source maps and tries to load them but there are no such source maps).

devtool is set to source-map for server-side builds.

Nodemon

I recommend using nodemon for running server-side Webpack bundle. Nodemon has a --watch <directory> command line parameter which restarts Node.js process each time the <directory> is updated (e.g. each time any file in that directory is modified).

In other words, Nodemon will relaunch the server every time the code is rebuilt with Webpack.

There's one little gotcha though: for the --watch feature to work the watched folder needs to exist by the time Nodemon is launched. That means that the server must be started only after the settings.server.output path folder has been created.

To accomplish that this library provides a command line tool: universal-webpack. No need to install in globally: it is supposed to work locally through npm scripts. Usage example:

package.json

...
  "scripts": {
    "start": "npm-run-all prepare-server-build start-development-workflow",
    "start-development-workflow": "npm-run-all --parallel development-webpack-build-for-client development-webpack-build-for-server development-start-server",
    "prepare-server-build": "universal-webpack --settings ./universal-webpack-settings.js prepare",
    ...

The prepare command creates settings.server.output path folder, or clears it if it already exists.

In a moderately sized React project server restart times can reach ~10 seconds. Therefore the right way to go is to extract React rendering server-side code into a separate Node.js process (service), and then in the main Node.js web server just proxy all unmatched URLs to this React rendering service, as explained in the following section. This way only React rendering service will be restarted, and the main Node.js web server will be left untouched.

Separate React rendering service from the main code

If the sole purpose of using universal-webpack in your project is to enable server-side rendering of web pages, then the best practice is to extract the web page rendering code from the main Node.js application into a separate Node.js application, and then in the main Node.js application just proxy all unmatched URLs to this React rendering service.

import http_proxy from 'http-proxy'

const react_service = `http://${react_rendering_service.host}:${react_rendering_service.port}`
const react_proxy = http_proxy.createProxyServer({ target: react_service })

// Various web application middleware (statics, API, etc)
app.use(...)
app.use(...)
app.use(...)

// In the end, if no middleware matched the incoming HTTP request URL
app.use((request, response) =>
{
    // Proxying failed
    response.on('close', () =>
    {
        // reject(new Error(`Http response closed while proxying`))
    })

    // Proxying finished
    response.on('finish', () =>
    {
        // resolve()
    })

    // Do the proxy
    react_proxy.web(request, response, (error) =>
    {
        // reject(error)

        response.writeHead(502)
        response.end("There was an error proxying your request")
    })
})

This way only the rendering service will have to be built with Webpack.

Flash of unstyled content

(this is an "advanced" section which can be safely skipped)

A "flash of unstyled content" is a well-known thing. One can observe it when refreshing the page in development mode: because Webpack's style-loader adds styles to the page dynamically there's a short period (a second maybe) when there are no CSS styles applied to the webpage (in production mode extract-text-webpack-plugin is used instead of style-loader so there's no "flash of unstyled content").

It's not really a bug, many projects live with it and it doesn't really affect the development process that much, so one can safely skip reading this section. It's just if you're a perfectionist then it can get a little itchy.

I came up with a sort of a slightly hacky solution which seems to be working. To enable the anti-unstyled-flash feature one needs to pass the third parameter to the client-side webpack configuration creation function - an options object with:

development key set to true indicating that it's a development build configuration
css_bundle key set to true

If both development and css_bundle options are set to true, then universal-webpack will enhance the client side Webpack configuration to also output all styles into a single CSS bundle (while retaining style-loader) which is later added to the webpage's <head/> as a <link rel="stylesheet"/> tag on the server side, therefore making that "flash of unstyled content" disappear.

There's a gotcha though. Because the whole CSS bundle gets inserted as a <link rel="stylesheet"/> tag in the <head/> it also means that the styles defined in that CSS bundle are static, not dynamic, and they aren't gonna "hot reload" themselves or something. So, my proposed solution is to have that <link rel="stylesheet"/> tag sit in the <head/> for a while (say, a couple of seconds) and then remove it from there. The styling of the webpage isn't gonna disappear at that moment because by that time the dynamic styles of style-loader have already kicked in. See an example of how this can be done.

import { client_configuration } from 'universal-webpack'
import settings from './universal-webpack-settings'
import configuration from './webpack.config'

export default client_configuration(configuration, settings, { development: true, css_bundle: true })

License

MIT