@kouhin/webpack-isomorphic-tools

v2.2.31

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2 years ago

Transforms CSS-alike text into a React style JSON object

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kouhin

react style inline css

webpack-isomorphic-tools

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Is a small helper module providing support for isomorphic (universal) rendering when using Webpack.

This is an alternative solution to using Webpack's target: "node" approach. For a target: "node" example refer to the corresponding sample project.

Which one of these approaches to take? I think it's just a matter of taste. Both solutions work. Both involve some level of complexity because this is an advanced topic (Webpack is Serious Business).

If you start feeling desperate and mad just clone one of the boilerplates and see it working. You may also check out the troubleshooting section if you're having some issues.

Topics

What it does and why is it needed?

What is a web application? I would define it as a box with a bunch of inputs (keyboard events, mouse events) and a display as an output. A user walks into your website and your web application renders a "page" on his display.

At first all the rendering used to happen on the server. But then "AJAX" came (in 2005) and it opened a possibility of moving all rendering logic to the client (user's web browser) leaving the server with just serving API calls (data fetching, data modification, etc).

And so numerous javascript frameworks emerged to serve the purpose of client side rendering and routing. But then everybody realised that this new way of building web applications broke search engine indexing because the search engines didn't talk any javascript.

Then the age of super-responsive websites came and also the iPhone emerged and the battle for milliseconds began. And everybody noticed that client side rendering introduced unnecessary data fetching roundtrips on the first page load: the web browser loaded markup templates and scripts first and then asked the server for the actual data to display.

So it became obvious that web applications need to be "isomorphic" ("universal"), i.e. be able to render both on the client and the server, depending on circumstances. It was quite manageable: one just had to write the rendering logic in such a programming language that is able to run both on client and server. One such language is javascript.

Time moved on and then another new technology emerged - bundling: web applications became so sophisticated and big that the programmers needed a software to take control of the development, testing and building process and to manage all the heterogeneous components of the system. Currently the most popular and well-thought bundler is Webpack.

But Webpack is made for client side code development only: it finds all require() calls inside your code and replaces them with various kinds of magic to make the things work. If you try to run the same source code outside of Webpack - for example, on a Node.js server - you'll get a ton of SyntaxErrors with Unexpected tokens. That's because on a Node.js server there's no Webpack require() magic happening and it simply tries to require() all the "assets" (styles, images, fonts, OpenGL shaders, etc) as if they were proper javascript-coded modules hence the error message.

This module - webpack-isomorphic-tools - aims to solve these issues and make the client-side code work on the server too therefore reclaiming isomorphic (universal) rendering capabilities. It provides the missing require() magic - same as Webpack does on client-side - when running your code on the server. With the help of webpack-isomorphic-tools one can fix all those webpack-ish require()s of assets and make them work on the server instead of throwing SyntaxErrors.

Getting down to business

For example, consider images. Images are require()d in React components and then used like this:

// alternatively one can use import, but in this case hot reloading won't work
// import image_path from '../image.png'

// you just `src` your image inside your `render()` method
class Photo extends React.Component
{
  render()
  {
    // when Webpack url-loader finds this `require()` call 
    // it will copy `image.png` to your build folder 
    // and name it something like `9059f094ddb49c2b0fa6a254a6ebf2ad.png`, 
    // because we are using the `[hash]` file naming feature of Webpack url-loader
    // which (feature) is required to make browser caching work correctly
    const image_path = require('../image.png')

    return <img src={image_path}/>
  }
}

It works on the client because Webpack intelligently replaces all the require() calls for you. But it wouldn't work on the server because Node.js only knows how to require() javascript modules. It would just throw a SyntaxError.

To solve this issue you use webpack-isomorphic-tools in your application and what it does is it makes the code above work on the server too so that you can have your isomorphic (universal) rendering working.

In this particular case the require() call will return the real path to the image on the disk. It would be something like ../../build/9059f094ddb49c2b0fa6a254a6ebf2ad.png. How did webpack-isomorphic-tools know this weird real file path? It's just a bit of magic.

So, you get the idea now?

Aside all of that, webpack-isomorphic-tools is highly extensible, and finding the real paths for your assets is just the simplest example of what you can do. Using custom configuration one can make require() calls (on the server) return whatever is needed (not just a String; it may be a JSON object, for example).

For example, if you're using Webpack css-loader modules feature (also referred to as "local styles") you can make require(*.css) calls return JSON objects with generated CSS class names like they do in react-redux-universal-hot-example (it's just a demonstration of what one can do with webpack-isomorphic-tools, and I'm not using this "modules" feature of ccs-plugin in my projects).

Installation

webpack-isomorphic-tools are required both for development and production

$ npm install webpack-isomorphic-tools --save

Usage

First you add webpack_isomorphic_tools plugin to your Webpack configuration.

webpack.config.js

var Webpack_isomorphic_tools_plugin = require('webpack-isomorphic-tools/plugin')

var webpack_isomorphic_tools_plugin = 
  // webpack-isomorphic-tools settings reside in a separate .js file 
  // (because they will be used in the web server code too).
  new Webpack_isomorphic_tools_plugin(require('./webpack-isomorphic-tools-configuration'))
  // also enter development mode since it's a development webpack configuration
  // (see below for explanation)
  .development()

// usual Webpack configuration
module.exports =
{
  context: '(required) your project path here',

  output:
  {
    publicPath: '(required) web path for static files here'
  },

  module:
  {
    loaders:
    [
      ...,
      {
        test: webpack_isomorphic_tools_plugin.regular_expression('images'),
        loader: 'url-loader?limit=10240', // any image below or equal to 10K will be converted to inline base64 instead
      }
    ]
  },

  plugins:
  [
    ...,

    webpack_isomorphic_tools_plugin
  ]

  ...
}

What does .development() method do? It enables development mode. In short, when in development mode, it disables asset caching (and enables asset hot reload). Just call it if you're developing your project with webpack-dev-server using this config (and, conversely, don't call it for your production webpack build - obvious enough).

For each asset type managed by webpack_isomorphic_tools there should be a corresponding loader in your Webpack configuration. For this reason webpack_isomorphic_tools/plugin provides a .regular_expression(asset_type) method. The asset_type parameter is taken from your webpack-isomorphic-tools configuration:

webpack-isomorphic-tools-configuration.js

import Webpack_isomorphic_tools_plugin from 'webpack-isomorphic-tools/plugin'

export default
{
  assets:
  {
    images:
    {
      extensions: ['png', 'jpg', 'gif', 'ico', 'svg']
    }
  }
}

That's it for the client side. Next, the server side. You create your server side instance of webpack-isomorphic-tools in the very main server javascript file (and your web application code will reside in some server.js file which is require()d in the bottom)

main.js

var Webpack_isomorphic_tools = require('webpack-isomorphic-tools')

// this must be equal to your Webpack configuration "context" parameter
var project_base_path = require('path').resolve(__dirname, '..')

// this global variable will be used later in express middleware
global.webpack_isomorphic_tools = new Webpack_isomorphic_tools(require('./webpack-isomorphic-tools-configuration'))
// enter development mode if needed 
// (you may also prefer to use a Webpack DefinePlugin variable)
.development(process.env.NODE_ENV === 'development')
// initializes a server-side instance of webpack-isomorphic-tools
// (the first parameter is the base path for your project
//  and is equal to the "context" parameter of you Webpack configuration)
// (if you prefer Promises over callbacks 
//  you can omit the callback parameter
//  and then it will return a Promise instead)
.server(project_base_path, function()
{
  // webpack-isomorphic-tools is all set now.
  // here goes all your web application code:
  require('./server')
})

Then you, for example, create an express middleware to render your pages on the server

import React from 'react'

// html page markup
import Html from './html'

// will be used in express_application.use(...)
export function page_rendering_middleware(request, response)
{
  // clear require() cache if in development mode
  // (makes asset hot reloading work)
  if (_development_)
  {
    webpack_isomorphic_tools.refresh()
  }

  // for react-router example of determining current page by URL take a look at this:
  // https://github.com/halt-hammerzeit/webapp/blob/master/code/server/webpage%20rendering.js
  const page_component = [determine your page component here using request.path]

  // for a Redux Flux store implementation you can see the same example:
  // https://github.com/halt-hammerzeit/webapp/blob/master/code/server/webpage%20rendering.js
  const flux_store = [initialize and populate your flux store depending on the page being shown]

  // render the page to string and send it to the browser as text/html
  response.send('<!doctype html>\n' +
        React.renderToString(<Html assets={webpack_isomorphic_tools.assets()} component={page_component} store={flux_store}/>))
}

And finally you use the assets inside the Html component's render() method

import React, {Component, PropTypes} from 'react'
import serialize from 'serialize-javascript'

export default class Html extends Component
{
  static propTypes =
  {
    assets    : PropTypes.object,
    component : PropTypes.object,
    store     : PropTypes.object
  }

  // a sidenote for "advanced" users:
  // (you may skip this)
  //
  // this file is usually not included in your Webpack build
  // because this React component is only needed for server side React rendering.
  //
  // so, if this React component is not `require()`d from anywhere in your client code,
  // then Webpack won't ever get here 
  // which means Webpack won't detect and parse any of the `require()` calls here,
  // which in turn means that if you `require()` any unique assets here 
  // you should also `require()` those assets somewhere in your client code,
  // otherwise those assets won't be present in your Webpack bundle and won't be found.
  //
  render()
  {
    const { assets, component, store } = this.props

    // "import" will work here too 
    // but if you want hot reloading to work while developing your project
    // then you need to use require()
    // because import will only be executed a single time 
    // (when the application launches)
    // you can refer to the "Require() vs import" section for more explanation
    const picture = require('../assets/images/cat.jpg')

    // favicon
    const icon = require('../assets/images/icon/32x32.png')

    const html = 
    (
      <html lang="en-us">
        <head>
          <meta charSet="utf-8"/>
          <title>xHamster</title>

          {/* favicon */}
          <link rel="shortcut icon" href={icon} />

          {/* styles (will be present only in production with webpack extract text plugin) */}
          {Object.keys(assets.styles).map((style, i) =>
            <link href={assets.styles[style]} key={i} media="screen, projection"
                  rel="stylesheet" type="text/css"/>)}

          {/* resolves the initial style flash (flicker) on page load in development mode */}
          { Object.keys(assets.styles).is_empty() ? <style dangerouslySetInnerHTML={{__html: require('../assets/styles/main_style.css')}}/> : null }
        </head>

        <body>
          {/* image requiring demonstration */}
          <img src={picture}/>

          {/* rendered React page */}
          <div id="content" dangerouslySetInnerHTML={{__html: React.renderToString(component)}}/>

          {/* Flux store data will be reloaded into the store on the client */}
          <script dangerouslySetInnerHTML={{__html: `window._flux_store_data=${serialize(store.getState())};`}} />

          {/* javascripts */}
          {/* (usually one for each "entry" in webpack configuration) */}
          {/* (for more informations on "entries" see https://github.com/petehunt/webpack-howto/) */}
          {Object.keys(assets.javascript).map((script, i) =>
            <script src={assets.javascript[script]} key={i}/>
          )}
        </body>
      </html>
    )

    return html
  }
}

assets in the code above are simply the contents of webpack-assets.json which is created by webpack-isomorphic-tools in your project base folder. webpack-assets.json (in the simplest case) keeps track of the real paths to your assets, e.g.

{
  "javascript":
  {
    "main": "/assets/main-d8c29e9b2a4623f696e8.js"
  },

  "styles":
  {
    "main": "/assets/main-d8c29e9b2a4623f696e8.css"
  },

  "assets":
  {
    "./assets/images/cat.jpg": "http://localhost:3001/assets/9059f094ddb49c2b0fa6a254a6ebf2ad.jpg",
    
    "./assets/images/icon/32x32.png": "data:image/png;base64,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"
  }
}

And that's it, now you can require() your assets "isomorphically" (both on client and server).

A working example

webpack-isomorphic-tools are featured in react-redux-universal-hot-example. There it is used to require() images and CSS styles (in the form of CSS modules).

Also you may look at this sample project. There it is used to require() images and CSS styles (without using CSS modules feature).

Some source code guidance for the aforementioned project:

Configuration

Available configuration parameters:

{
  // sets "development" mode flag.
  // see the API section below for method .development()
  // for more explanation about what "development" mode does
  // and when is it needed.
  //
  development: true, // is false by default

  // debug mode.
  // when set to true, lets you see debugging messages in the console.
  //
  debug: true, // is false by default

  // verbosity.
  // when set to true, outputs Webpack stats to the console 
  // in development mode on each incremental build.
  // (i don't know who might need that info)
  //
  // verbose: true, // is false by default

  // enables support for `require.context()` function.
  // is turned off by default 
  // to skip unnecessary code instrumentation
  // because not everyone uses it.
  //
  // require_context: true, // is false by default

  // By default it creates 'webpack-assets.json' file at 
  // webpack_configuration.context (which is your project folder).
  // You can change the assets file path as you wish
  // (therefore changing both folder and filename).
  //
  // (relative to webpack_configuration.context which is your project folder)
  //
  webpack_assets_file_path: 'webpack-assets.json',

  // By default, when running in debug mode, it creates 'webpack-stats.json' file at 
  // webpack_configuration.context (which is your project folder).
  // You can change the stats file path as you wish
  // (therefore changing both folder and filename).
  //
  // (relative to webpack_configuration.context which is your project folder)
  //
  webpack_stats_file_path: 'webpack-stats.json',

  // Makes `webpack-isomorphic-tools` aware of Webpack aliasing feature
  // (if you use it)
  // https://webpack.github.io/docs/resolving.html#aliasing
  //
  // The `alias` parameter corresponds to `resolve.alias` 
  // in your Webpack configuration.
  //
  alias: webpack_configuration.resolve.alias, // is {} by default

  // if you're using Webpack's `resolve.modulesDirectories`
  // then you should also put them here.
  //
  // modulesDirectories: webpack_configuration.resolve.modulesDirectories // is ['node_modules'] by default

  // here you can define all your asset types
  //
  assets:
  {
    // asset_type will appear in:
    //  * webpack-assets.json
    //  * .assets() method call result
    //  * .regular_expression(asset_type) method call
    //
    asset_type: 
    {
      // which file types belong to this asset type
      //
      extension: 'png', // or extensions: ['png', 'jpg', ...],

      // here you are able to add some file paths 
      // for which the require() call will bypass webpack-isomorphic-tools
      // (relative to the project base folder, e.g. ./sources/server/kitten.jpg.js)
      // (also supports regular expressions, e.g. /^\.\/node_modules\/*/, 
      //  and functions(path) { return true / false })
      //
      exclude: [],

      // here you can specify manually the paths 
      // for which the require() call will be processed by webpack-isomorphic-tools
      // (relative to the project base folder, e.g. ./sources/server/kitten.jpg.js)
      // (also supports regular expressions, e.g. /^\.\/node_modules\/*/, 
      //  and functions(path) { return true / false }).
      // in case of `include` only included paths will be processed by webpack-isomorphic-tools.
      //
      include: [],

      // [optional]
      // 
      // determines which webpack stats modules 
      // belong to this asset type
      //
      // arguments:
      //
      //  module             - a webpack stats module
      //
      //                       (to understand what a "module" is
      //                        read the "What's a "module"?" section of this readme)
      //
      //  regular_expression - a regular expression 
      //                       composed of this asset type's extensions
      //                       e.g. /\.scss$/, /\.(ico|gif)$/
      //
      //  options            - various options
      //                       (development mode flag,
      //                        debug mode flag,
      //                        assets base url,
      //                        project base folder,
      //                        regular_expressions{} for each asset type (by name),
      //                        webpack stats json object)
      //
      //  log
      // 
      // returns: a Boolean
      //
      // by default is: "return regular_expression.test(module.name)"
      //
      // premade utility filters:
      //
      // Webpack_isomorphic_tools_plugin.style_loader_filter
      //  (for use with style-loader + css-loader)
      //
      filter: function(module, regular_expression, options, log)
      {
        return regular_expression.test(module.name)
      },

      // [optional]
      //
      // transforms a webpack stats module name 
      // to an asset path (usually is the same thing)
      //
      // arguments:
      //
      //  module  - a webpack stats module
      //
      //            (to understand what a "module" is
      //             read the "What's a "module"?" section of this readme)
      //
      //  options - various options
      //            (development mode flag,
      //             debug mode flag,
      //             assets base url,
      //             project base folder,
      //             regular_expressions{} for each asset type (by name),
      //             webpack stats json object)
      //
      //  log
      // 
      // returns: a String
      //
      // by default is: "return module.name"
      //
      // premade utility path extractors:
      //
      // Webpack_isomorphic_tools_plugin.style_loader_path_extractor
      //  (for use with style-loader + css-loader)
      //
      path: function(module, options, log)
      {
        return module.name
      },

      // [optional]
      // 
      // parses a webpack stats module object
      // for an asset of this asset type
      // to whatever you need to get 
      // when you require() these assets 
      // in your code later on.
      //
      // this is what you'll see as the asset value in webpack-assets.json: 
      // { ..., path(): compile(parser()), ... }
      //
      // can be a CommonJS module source code:
      // module.exports = ...what you export here is 
      //                     what you get when you require() this asset...
      //
      // if the returned value is not a CommonJS module source code
      // (it may be a string, a JSON object, whatever) 
      // then it will be transformed into a CommonJS module source code.
      //
      // in other words: 
      //
      // // making of webpack-assets.json
      // for each type of configuration.assets
      //   modules.filter(type.filter).for_each (module)
      //     assets[type.path()] = compile(type.parser(module))
      //
      // // requiring assets in your code
      // require(path) = (path) => return assets[path]
      //
      // arguments:
      //
      //  module  - a webpack stats module
      //
      //            (to understand what a "module" is
      //             read the "What's a "module"?" section of this readme)
      //
      //  options - various options
      //            (development mode flag,
      //             debug mode flag,
      //             assets base url,
      //             project base folder,
      //             regular_expressions{} for each asset type (by name),
      //             webpack stats json object)
      //
      //  log
      // 
      // returns: whatever (could be a filename, could be a JSON object, etc)
      //
      // by default is: "return module.source"
      //
      // premade utility parsers:
      //
      // Webpack_isomorphic_tools_plugin.url_loader_parser
      //  (for use with url-loader or file-loader)
      //  require() will return file URL
      //  (is equal to the default parser, i.e. no parser)
      //
      // Webpack_isomorphic_tools_plugin.css_loader_parser
      //  (for use with css-loader when not using "modules" feature)
      //  require() will return CSS style text
      //
      // Webpack_isomorphic_tools_plugin.css_modules_loader_parser
      //  (for use with css-loader when using "modules" feature)
      //  require() will return a JSON object map of style class names
      //  which will also have a `_style` key containing CSS style text
      //
      parser: function(module, options, log)
      {
        log.info('# module name', module.name)
        log.info('# module source', module.source)
        log.info('# project path', options.project_path)
        log.info('# assets base url', options.assets_base_url)
        log.info('# regular expressions', options.regular_expressions)
        log.info('# debug mode', options.debug)
        log.info('# development mode', options.development)
        log.debug('debugging')
        log.warning('warning')
        log.error('error')
      }
    },
    ...
  },
  ...]
}

Configuration examples

url-loader / file-loader (images, fonts, etc)

url-loader and file-loader are supported with no additional configuration

{
  assets:
  {
    images:
    {
      extensions: ['png', 'jpg']
    },

    fonts:
    {
      extensions: ['woff', 'ttf']
    }
  }
}

style-loader (standard CSS stylesheets)

If you aren't using "CSS modules" feature of Webpack, and if in your production Webpack config you use ExtractTextPlugin for CSS styles, then you can set it up like this

{
  assets:
  {
    styles:
    {
      extensions: ['less', 'scss'],

      // which `module`s to parse CSS from:
      filter: function(module, regular_expression, options, log)
      {
        if (options.development)
        {
          // In development mode there's Webpack "style-loader",
          // which outputs `module`s with `module.name == asset_path`,
          // but those `module`s do not contain CSS text.
          //
          // The `module`s containing CSS text are 
          // the ones loaded with Webpack "css-loader".
          // (which have kinda weird `module.name`)
          //
          // Therefore using a non-default `filter` function here.
          //
          return webpack_isomorphic_tools_plugin.style_loader_filter(module, regular_expression, options, log)
        }

        // In production mode there will be no CSS text at all
        // because all styles will be extracted by Webpack Extract Text Plugin
        // into a .css file (as per Webpack configuration).
        //
        // Therefore in production mode `filter` function always returns non-`true`.
      },

      // How to correctly transform kinda weird `module.name`
      // of the `module` created by Webpack "css-loader" 
      // into the correct asset path:
      path: webpack_isomorphic_tools_plugin.style_loader_path_extractor,

      // How to extract these Webpack `module`s' javascript `source` code.
      // basically takes `module.source` and modifies `module.exports` a little.
      parser: webpack_isomorphic_tools_plugin.css_loader_parser
    }
  }
}

style-loader (CSS stylesheets with "CSS modules" feature)

If you are using "CSS modules" feature of Webpack, and if in your production Webpack config you use ExtractTextPlugin for CSS styles, then you can set it up like this

{
  assets:
  {
    style_modules:
    {
      extensions: ['less', 'scss'],

      // which `module`s to parse CSS style class name maps from:
      filter: function(module, regex, options, log)
      {
        if (options.development)
        {
          // In development mode there's Webpack "style-loader",
          // which outputs `module`s with `module.name == asset_path`,
          // but those `module`s do not contain CSS text.
          //
          // The `module`s containing CSS text are 
          // the ones loaded with Webpack "css-loader".
          // (which have kinda weird `module.name`)
          //
          // Therefore using a non-default `filter` function here.
          //
          return webpack_isomorphic_tools_plugin.style_loader_filter(module, regex, options, log)
        }

        // In production mode there's no Webpack "style-loader",
        // so `module.name`s of the `module`s created by Webpack "css-loader"
        // (those which contain CSS text)
        // will be simply equal to the correct asset path
        return regex.test(module.name)
      },

      // How to correctly transform `module.name`s
      // into correct asset paths
      path: function(module, options, log)
      {
        if (options.development)
        {
          // In development mode there's Webpack "style-loader",
          // so `module.name`s of the `module`s created by Webpack "css-loader"
          // (those picked by the `filter` function above)
          // will be kinda weird, and this path extractor extracts 
          // the correct asset paths from these kinda weird `module.name`s
          return WebpackIsomorphicToolsPlugin.style_loader_path_extractor(module, options, log);
        }

        // in production mode there's no Webpack "style-loader",
        // so `module.name`s will be equal to correct asset paths
        return module.name
      },

      // How to extract these Webpack `module`s' javascript `source` code.
      // Basically takes `module.source` and modifies its `module.exports` a little.
      parser: function(module, options, log)
      {
        if (options.development)
        {
          // In development mode it adds an extra `_style` entry
          // to the CSS style class name map, containing the CSS text
          return WebpackIsomorphicToolsPlugin.css_modules_loader_parser(module, options, log);
        }

        // In production mode there's Webpack Extract Text Plugin 
        // which extracts all CSS text away, so there's
        // only CSS style class name map left.
        return module.source
      }
    }
  }
}

What are webpack-assets.json?

This file is needed for webpack-isomorphic-tools operation on server. It is created by a custom Webpack plugin and is then read from the filesystem by webpack-isomorphic-tools server instance. When you require(path_to_an_asset) an asset on server then what you get is simply what's there in this file corresponding to this path_to_an_asset key (under the assets section).

Pseudocode:

// requiring assets in your code
require(path) = (path) => return assets[path]

Therefore, if you get such a message in the console:

[webpack-isomorphic-tools] [error] asset not found: ./~/react-toolbox/lib/font_icon/style.scss

Then it means that the asset you requested (require()d) is absent from your webpack-assets.json which in turn means that you haven't placed this asset to your webpack-assets.json in the first place. How to place an asset into webpack-assets.json?

Pseudocode:

// making of webpack-assets.json inside the Webpack plugin
for each type of configuration.assets
  modules.filter(type.filter).for_each (module)
    assets[type.path()] = compile(type.parser(module))

Therefore, if you get the "asset not found" error, first check your webpack-assets.json and second check your webpack-isomorphic-tools configuration section for this asset type: are your filter, path and parser functions correct?

What are Webpack stats?

Webpack stats are a description of all the modules in a Webpack build. When running in debug mode Webpack stats are output to a file named webpack-stats.json in the same folder as your webpack-assets.json file. One may be interested in the contents of this file when writing custom filter, path or parser functions. This file is not needed for operation, it's just some debugging information.

What's a "module"?

This is an advanced topic on Webpack internals

A "module" is a Webpack entity. One of the main features of Webpack is code splitting. When Webpack builds your code it splits it into "chunks" - large portions of code which can be downloaded separately later on (if needed) therefore reducing the initial page load time for your website visitor. These big "chunks" aren't monolithic and in their turn are composed of "modules" which are: standard CommonJS javascript modules you require() every day, pictures, stylesheets, etc. Every time you require() something (it could be anything: an npm module, a javascript file, or a css style, or an image) a module entry is created by Webpack. And the file where this require() call originated is called a reason for this require()d module. Each module entry has a name and a source code, along with a list of chunks it's in and a bunch of other miscellaneous irrelevant properties.

For example, here's a piece of an example webpack-stats.json file (which is generated along with webpack-assets.json in debug mode). Here you can see a random module entry created by Webpack.

{
  ...

  "modules": [
    {
      "id": 0,
      ...
    },
    {
      "id": 1,
      "name": "./~/fbjs/lib/invariant.js",
      "source": "module.exports = global[\"undefined\"] = require(\"-!G:\\\\work\\\\isomorphic-demo\\\\node_modules\\\\fbjs\\\\lib\\\\invariant.js\");",

      // the rest of the fields are irrelevant

      "chunks": [
        0
      ],
      "identifier": "G:\\work\\isomorphic-demo\\node_modules\\expose-loader\\index.js?undefined!G:\\work\\isomorphic-demo\\node_modules\\fbjs\\lib\\invariant.js",
      "index": 27,
      "index2": 7,
      "size": 117,
      "cacheable": true,
      "built": true,
      "optional": false,
      "prefetched": false,
      "assets": [],
      "issuer": "G:\\work\\isomorphic-demo\\node_modules\\react\\lib\\ReactInstanceHandles.js",
      "failed": false,
      "errors": 0,
      "warnings": 0,

      "reasons": [
        {
          "moduleId": 418,
          "moduleIdentifier": "G:\\work\\isomorphic-demo\\node_modules\\react\\lib\\ReactInstanceHandles.js",
          "module": "./~/react/lib/ReactInstanceHandles.js",
          "moduleName": "./~/react/lib/ReactInstanceHandles.js",
          "type": "cjs require",
          "userRequest": "fbjs/lib/invariant",
          "loc": "17:16-45"
        },
        ...
        {
          "moduleId": 483,
          "moduleIdentifier": "G:\\work\\isomorphic-demo\\node_modules\\react\\lib\\traverseAllChildren.js",
          "module": "./~/react/lib/traverseAllChildren.js",
          "moduleName": "./~/react/lib/traverseAllChildren.js",
          "type": "cjs require",
          "userRequest": "fbjs/lib/invariant",
          "loc": "19:16-45"
        }
      ]
    },

    ...
  ]
}

Judging by its reasons and their userRequests one can deduce that this module is require()d by many other modules in this project and the code triggering this module entry creation could look something like this

var invariant = require('fbjs/lib/invariant')

Every time you require() anything in your code, Webpack detects it during build process and the require()d module is "loaded" (decorated, transformed, replaced, etc) by a corresponding module "loader" (or loaders) specified in Webpack configuration file (webpack.conf.js) under the "module.loaders" path. For example, say, all JPG images in a project are configured to be loaded with a "url-loader":

// Webpack configuration
module.exports =
{
  ...

  module:
  {
    loaders:
    [
      ...

      {
        test   : /\.jpg$/,
        loader : 'url-loader'
      }
    ]
  },

  ...
}

This works on client: require() calls will return URLs for JPG images. The next step is to make require() calls to these JPG images behave the same way when this code is run on the server, with the help of webpack-isomorphic-tools. So, the fields of interest of the module object would be name and source: first you find the modules of interest by their names (in this case, the module names would end in ".jpg") and then you parse the sources of those modules to extract the information you need (in this case that would be the real path to an image).

The module object for an image would look like this

{
  ...
  "name": "./assets/images/husky.jpg",
  "source": "module.exports = __webpack_public_path__ + \"9059f094ddb49c2b0fa6a254a6ebf2ad.jpg\""
}

Therefore, in this simple case, in webpack-isomorphic-tools configuration file we create an "images" asset type with extension "jpg" and these parameters:

the filter function would be module => module.name.ends_with('.jpg') (and it's the default filter if no filter is specified)
the path parser function would be module => module.name (and it's the default path parser if no path parser is specified)
the parser function would be module => module.source (and it's the default parser if no parser is specified)

When the javascript source code returned by this parser function gets compiled by webpack-isomorphic-tools it will yeild a valid CommonJS javascript module which will return the URL for this image, resulting in the following piece of webpack-assets.json:

{
  ...
  assets:
  {
     "./assets/images/husky.jpg": "/assets/9059f094ddb49c2b0fa6a254a6ebf2ad.jpg",
     ...
  }
}

And so when you later require("./assets/images/husky.jpg") in your server code it will return "/assets/9059f094ddb49c2b0fa6a254a6ebf2ad.jpg" and that's it.

API

Constructor

(both Webpack plugin and server tools)

Takes an object with options (see Configuration section above)

.development(true or false or undefined -> true)

(both Webpack plugin instance and server tools instance)

Is it development mode or is it production mode? By default it's production mode. But if you're instantiating webpack-isomorphic-tools/plugin for use in Webpack development configuration, or if you're instantiating webpack-isomorphic-tools on server when you're developing your project, then you should call this method to enable asset hot reloading (and disable asset caching). It should be called right after the constructor.

.regular_expression(asset_type)

(Webpack plugin instance)

Returns the regular expression for this asset type (based on this asset type's extension (or extensions))

Webpack_isomorphic_tools_plugin.url_loader_parser

(Webpack plugin)

A parser (see Configuration section above) for Webpack url-loader, also works for Webpack file-loader. Use it for your images, fonts, etc.

.server(project_path, [callback])

(server tools instance)

Initializes a server-side instance of webpack-isomorphic-tools with the base path for your project and makes all the server-side require() calls work. The project_path parameter must be identical to the context parameter of your Webpack configuration and is needed to locate webpack-assets.json (contains the assets info) which is output by Webpack process.

When you're running your project in development mode for the very first time the webpack-assets.json file doesn't exist yet because in development mode webpack-dev-server and your application server are run concurrently and by the time the application server starts the webpack-assets.json file hasn't yet been generated by Webpack and require() calls for your assets would return undefined.

To fix this you can put your application server code into a callback and pass it as a second parameter and it will be called as soon as webpack-assets.json file is detected. If not given a callback this method will return a Promise which is fulfilled as soon as webpack-assets.json file is detected (in case you prefer Promises over callbacks). When choosing a Promise way you won't be able to get the webpack-isomorphic-tools instance variable reference out of the .server() method call result, so your code can be a bit more verbose in this case.

.refresh()

(server tools instance)

Refreshes your assets info (re-reads webpack-assets.json from disk) and also flushes cache for all the previously require()d assets

.assets()

(server tools instance)

Returns the contents of webpack-assets.json which is created by webpack-isomorphic-tools in your project base folder

Troubleshooting

Cannot find module

If encountered when run on server, this error means that the require()d path doesn't exist in the filesystem (all the require()d assets must exist in the filesystem when run on server). If encountered during Webpack build, this error means that the require()d path is absent from webpack-stats.json.

SyntaxError: Unexpected token ILLEGAL

This probably means that in some asset module source there's a require() call to some file extension that isn't specified in

TypeError: require.context is not a function

You should enable require_context: true flag in your webpack-isomorphic-tools configuration file. The reason is that the support for require.context() is hacky at the moment. It works and does its thing but the solution is not elegant enough if you know what I mean.

Support for require.context() is in alpha stage. If you encounter any bugs report them in the issues.

Infinite "(waiting for the first Webpack build to finish)"

If you're getting this message infinitely then it means that webpack-assets.json is never generated by Webpack.

It can happen, for example, in any of these cases

you forgot to add webpack-isomorphic-tools plugin to your Webpack configuration
you aren't running your Webpack build either in parallel with your app or prior to running you app
you're using webpack-dev-middleware inside your main server code which you shouldn't
your Webpack configuration's context path doesn't point to the project base directory

If none of those is your case, enable debug: true flag in webpack-isomorphic-tools configuration to get debugging info.

Miscellaneous

.gitignore

Make sure you add this to your .gitignore so that you don't commit these unnecessary files to your repo

# webpack-isomorphic-tools
/webpack-stats.json
/webpack-assets.json

Require() vs import

In the image requiring examples above we could have wrote it like this:

import picture from './cat.jpg'

That would surely work. Much simpler and more modern. But, the disadvantage of the new ES6 module importing is that by design it's static as opposed to dynamic nature of require(). Such a design decision was done on purpose and it's surely the right one:

it's static so it can be optimized by the compiler and you don't need to know which module depends on which and manually reorder them in the right order because the compiler does it for you
it's smart enough to resolve cyclic dependencies
it can load modules both synchronously and asynchronously if it wants to and you'll never know because it can do it all by itself behind the scenes without your supervision
the exports are static which means that your IDE can know exactly what each module is gonna export without compiling the code (and therefore it can autocomplete names, detect syntax errors, check types, etc); the compiler too has some benefits such as improved lookup speed and syntax and type checking
it's simple, it's transparent, it's sane

If you wrote your code with just imports it would work fine. But imagine you're developing your website, so you're changing files constantly, and you would like it all refresh automagically when you reload your webpage (in development mode). webpack-isomorphic-tools gives you that. Remember this code in the express middleware example above?

if (_development_)
{
  webpack_isomorhic_tools.refresh()
}

It does exactly as it says: it refreshes everything on page reload when you're in development mode. And to leverage this feature you need to use dynamic module loading as opposed to static one through imports. This can be done by require()ing your assets, and not at the top of the file where all require()s usually go but, say, inside the reder() method for React components.

I also read on the internets that ES6 supports dynamic module loading too and it looks something like this:

System.import('some_module')
.then(some_module =>
{
  // Use some_module
})
.catch(error =>
{
  ...
})

I'm currently unfamiliar with ES6 dynamic module loading system because I didn't research this question. Anyway it's still a draft specification so I guess good old require() is just fine to the time being.

Also it's good to know that the way all this require('./asset.whatever_extension') magic is based on Node.js require hooks and it works with imports only when your ES6 code is transpiled by Babel which simply replaces all the imports with require()s. For now, everyone out there uses Babel, both on client and server. But when the time comes for ES6 to be widely natively adopted, and when a good enough ES6 module loading specification is released, then I (or someone else) will port this "require hook" to ES6 to work with imports.

References

Initially based on the code from react-redux-universal-hot-example by Erik Rasmussen

Also the same codebase (as in the project mentioned above) can be found in isomorphic500 by Giampaolo Bellavite

Also uses require() hooking techniques from node-hook by Gleb Bahmutov

Contributing

After cloning this repo, ensure dependencies are installed by running:

npm install

This module is written in ES6 and uses Babel for ES5 transpilation. Widely consumable JavaScript can be produced by running:

npm run build

Once npm run build has run, you may import or require() directly from node.

After developing, the full test suite can be evaluated by running:

npm test

While actively developing, one can use (personally I don't use it)

npm run watch

in a terminal. This will watch the file system and run tests automatically whenever you save a js file.

When you're ready to test your new functionality on a real project, you can run

npm pack

It will build, test and then create a .tgz archive which you can then install in your project folder

npm install [module name with version].tar.gz

To do

Implement require.context(folder, include_subdirectories, regular_expression) Webpack helper function properly
Proper testing for log (output to a variable rather than console)
Proper testing for notify_stats (output to a log variable)
Proper testing for parsers (using eval() CommonJS module compilation)
Proper testing for require('./node_modules/whatever.jpg') test case

License

MIT [npm-image]: https://img.shields.io/npm/v/webpack-isomorphic-tools.svg [npm-url]: https://npmjs.org/package/webpack-isomorphic-tools [travis-image]: https://img.shields.io/travis/halt-hammerzeit/webpack-isomorphic-tools/master.svg [travis-url]: https://travis-ci.org/halt-hammerzeit/webpack-isomorphic-tools [downloads-image]: https://img.shields.io/npm/dm/webpack-isomorphic-tools.svg [downloads-url]: https://npmjs.org/package/webpack-isomorphic-tools [coveralls-image]: https://img.shields.io/coveralls/halt-hammerzeit/webpack-isomorphic-tools/master.svg [coveralls-url]: https://coveralls.io/r/halt-hammerzeit/webpack-isomorphic-tools?branch=master

Published

Vulnerabilities

Links

Maintainers

Keywords

Readme

webpack-isomorphic-tools

Topics

What it does and why is it needed?

Getting down to business

Installation

Usage

webpack.config.js

webpack-isomorphic-tools-configuration.js

main.js

A working example

Configuration

Configuration examples

url-loader / file-loader (images, fonts, etc)

style-loader (standard CSS stylesheets)

style-loader (CSS stylesheets with "CSS modules" feature)

What are webpack-assets.json?

What are Webpack stats?

What's a "module"?

API

Constructor

.development(true or false or undefined -> true)

.regular_expression(asset_type)

Webpack_isomorphic_tools_plugin.url_loader_parser

.server(project_path, [callback])

.refresh()

.assets()

Troubleshooting

Cannot find module

SyntaxError: Unexpected token ILLEGAL

TypeError: require.context is not a function

Infinite "(waiting for the first Webpack build to finish)"

Miscellaneous

.gitignore

Require() vs import

References

Contributing

To do

License