{"rowid": 37, "title": "JavaScript Modules the ES6 Way", "contents": "JavaScript admittedly has plenty of flaws, but one of the largest and most prominent is the lack of a module system: a way to split up your application into a series of smaller files that can depend on each other to function correctly. \n\nThis is something nearly all other languages come with out of the box, whether it be Ruby\u2019s require, Python\u2019s import, or any other language you\u2019re familiar with. Even CSS has @import! JavaScript has nothing of that sort, and this has caused problems for  application developers as they go from working with small websites to full client-side applications. Let\u2019s be clear: it doesn\u2019t mean the new module system in the upcoming version of JavaScript won\u2019t be useful to you if you\u2019re building smaller websites rather than the next Instagram.\n\nThankfully, the lack of a module system will soon be a problem of the past. The next version of JavaScript, ECMAScript 6, will bring with it a full-featured module and dependency management solution for JavaScript. The bad news is that it won\u2019t be landing in browsers for a while yet \u2013 but the good news is that the specification for the module system and how it will look has been finalised. The even better news is that there are tools available to get it all working in browsers today without too much hassle. In this post I\u2019d like to give you the gift of JS modules and show you the syntax, and how to use them in browsers today. It\u2019s much simpler than you might think.\n\nWhat is ES6?\n\nECMAScript is a scripting language that is standardised by a company called Ecma International. JavaScript is an implementation of ECMAScript. ECMAScript 6 is simply the next version of the ECMAScript standard and, hence, the next version of JavaScript. The spec aims to be fully comfirmed and complete by the end of 2014, with a target initial release date of June 2015. It\u2019s impossible to know when we will have full feature support across the most popular browsers, but already some ES6 features are landing in the latest builds of Chrome and Firefox. You shouldn\u2019t expect to be able to use the new features across browsers without some form of additional tooling or library for a while yet.\n\nThe ES6 module spec\n\nThe ES6 module spec was fully confirmed in July 2014, so all the syntax I will show you in this article is not expected to change. I\u2019ll first show you the syntax and the new APIs being added to the language, and then look at how to use them today. There are two parts to the new module system. The first is the syntax for declaring modules and dependencies in your JS files, and the second is a programmatic API for loading in modules manually. The first is what most people are expected to use most of the time, so it\u2019s what I\u2019ll focus on more.\n\nModule syntax\n\nThe key thing to understand here is that modules have two key components. First, they have dependencies. These are things that the module you are writing depends on to function correctly. For example, if you were building a carousel module that used jQuery, you would say that jQuery is a dependency of your carousel. You import these dependencies into your module, and we\u2019ll see how to do that in a minute. Second, modules have exports. These are the functions or variables that your module exposes publicly to anything that imports it. Using jQuery as the example again, you could say that jQuery exports the $ function. Modules that depend on and hence import jQuery get access to the $ function, because jQuery exports it.\n\nAnother important thing to note is that when I discuss a module, all I really mean is a JavaScript file. There\u2019s no extra syntax to use other than the new ES6 syntax. Once ES6 lands, modules and files will be analogous.\n\nNamed exports\n\nModules can export multiple objects, which can be either plain old variables or JavaScript functions. You denote something to be exported with the export keyword:\n\nexport function double(x) {\n  return x + x;\n};\n\n\nYou can also store something in a variable then export it. If you do that, you have to wrap the variable in a set of curly braces.\n\nvar double = function(x) {\n  return x + x;\n}\n\nexport { double };\n\nA module can then import the double function like so:\n\nimport { double } from 'mymodule';\ndouble(2); // 4\n\nAgain, curly braces are required around the variable you would like to import. It\u2019s also important to note that from 'mymodule' will look for a file called mymodule.js in the same directory as the file you are requesting the import from. There is no need to add the .js extension.\n\nThe reason for those extra braces is that this syntax lets you export multiple variables:\n\nvar double = function(x) {\n  return x + x;\n}\n\nvar square = function(x) {\n  return x * x;\n}\n\nexport { double, square }\n\nI personally prefer this syntax over the export function \u2026, but only because it makes it much clearer to me what the module exports. Typically I will have my export {\u2026} line at the bottom of the file, which means I can quickly look in one place to determine what the module is exporting.\n\nA file importing both double and square can do so in just the way you\u2019d expect:\n\nimport { double, square } from 'mymodule';\ndouble(2); // 4\nsquare(3); // 9\n\nWith this approach you can\u2019t easily import an entire module and all its methods. This is by design \u2013 it\u2019s much better and you\u2019re encouraged to import just the functions you need to use.\n\nDefault exports\n\nAlong with named exports, the system also lets a module have a default export. This is useful when you are working with a large library such as jQuery, Underscore, Backbone and others, and just want to import the entire library. A module can define its default export (it can only ever have one default export) like so:\n\nexport default function(x) {\n  return x + x;\n}\n\nAnd that can be imported:\n\nimport double from 'mymodule';\ndouble(2); // 4\n\n\nThis time you do not use the curly braces around the name of the object you are importing. Also notice how you can name the import whatever you\u2019d like. Default exports are not named, so you can import them as anything you like:\n\nimport christmas from 'mymodule';\nchristmas(2); // 4\n\nThe above is entirely valid.\n\nAlthough it\u2019s not something that is used too often, a module can have both named exports and a default export, if you wish.\n\nOne of the design goals of the ES6 modules spec was to favour default exports. There are many reasons behind this, and there is a very detailed discussion on the ES Discuss site about it. That said, if you find yourself preferring named exports, that\u2019s fine, and you shouldn\u2019t change that to meet the preferences of those designing the spec.\n\nProgrammatic API\n\nAlong with the syntax above, there is also a new API being added to the language so you can programmatically import modules. It\u2019s pretty rare you would use this, but one obvious example is loading a module conditionally based on some variable or property. You could easily import a polyfill, for example, if the user\u2019s browser didn\u2019t support a feature your app relied on. An example of doing this is:\n\nif(someFeatureNotSupported) {\n  System.import('my-polyfill').then(function(myPolyFill) {\n    // use the module from here\n  });\n}\n\nSystem.import will return a promise, which, if you\u2019re not familiar, you can read about in this excellent article on HTMl5 Rocks by Jake Archibald. A promise basically lets you attach callback functions that are run when the asynchronous operation (in this case, System.import), is complete.\n\nThis programmatic API opens up a lot of possibilities and will also provide hooks to allow you to register callbacks that will run at certain points in the lifetime of a module. Those hooks and that syntax are slightly less set in stone, but when they are confirmed they will provide really useful functionality. For example, you could write code that would run every module that you import through something like JSHint before importing it. In development that would provide you with an easy way to keep your code quality high without having to run a command line watch task.\n\nHow to use it today\n\nIt\u2019s all well and good having this new syntax, but right now it won\u2019t work in any browser \u2013 and it\u2019s not likely to for a long time. Maybe in next year\u2019s 24 ways there will be an article on how you can use ES6 modules with no extra work in the browser, but for now we\u2019re stuck with a bit of extra work.\n\nES6 module transpiler\n\nOne solution is to use the ES6 module transpiler, a compiler that lets you write your JavaScript using the ES6 module syntax (actually a subset of it \u2013 not quite everything is supported, but the main features are) and have it compiled into either CommonJS-style code (CommonJS is the module specification that NodeJS and Browserify use), or into AMD-style code (the spec RequireJS uses). There are also plugins for all the popular build tools, including Grunt and Gulp.\n\nThe advantage of using this transpiler is that if you are already using a tool like RequireJS or Browserify, you can drop the transpiler in, start writing in ES6 and not worry about any additional work to make the code work in the browser, because you should already have that set up already. If you don\u2019t have any system in place for handling modules in the browser, using the transpiler doesn\u2019t really make sense. Remember, all this does is convert ES6 module code into CommonJS- or AMD-compliant JavaScript. It doesn\u2019t do anything to help you get that code running in the browser, but if you have that part sorted it\u2019s a really nice addition to your workflow. If you would like a tutorial on how to do this, I wrote a post back in June 2014 on using ES6 with the ES6 module transpiler.\n\nSystemJS\n\nAnother solution is SystemJS. It\u2019s the best solution in my opinion, particularly if you are starting a new project from scratch, or want to use ES6 modules on a project where you have no current module system in place. SystemJS is a spec-compliant universal module loader: it loads ES6 modules, AMD modules, CommonJS modules, as well as modules that just add a variable to the global scope (window, in the browser).\n\nTo load in ES6 files, SystemJS also depends on two other libraries: the ES6 module loader polyfill; and Traceur. Traceur is best accessed through the bower-traceur package, as the main repository doesn\u2019t have an easy to find downloadable version. The ES6 module load polyfill implements System.import, and lets you load in files using it. Traceur is an ES6-to-ES5 module loader. It takes code written in ES6, the newest version of JavaScript, and transpiles it into ES5, the version of JavaScript widely implemented in browsers. The advantage of this is that you can play with the new features of the language today, even though they are not supported in browsers. The drawback is that you have to run all your files through Traceur every time you save them, but this is easily automated. Additionally, if you use SystemJS, the Traceur compilation is done automatically for you.\n\nAll you need to do to get SystemJS running is to add a <script> element to load SystemJS into your webpage. It will then automatically load the ES6 module loader and Traceur files when it needs them. In your HTML you then need to use System.import to load in your module:\n\n<script>\n  System.import('./app');\n</script>\n\nWhen you load the page, app.js will be asynchronously loaded. Within app.js, you can now use ES6 modules. SystemJS will detect that the file is an ES6 file, automatically load Traceur, and compile the file into ES5 so that it works in the browser. It does all this dynamically in the browser, but there are tools to bundle your application in production, so it doesn\u2019t make a lot of requests on the live site. In development though, it makes for a really nice workflow.\n\nWhen working with SystemJS and modules in general, the best approach is to have a main module (in our case app.js) that is the main entry point for your application. app.js should then be responsible for loading all your application\u2019s modules. This forces you to keep your application organised by only loading one file initially, and having the rest dealt with by that file.\n\nSystemJS also provides a workflow for bundling your application together into one file.\n\nConclusion\n\nES6 modules may be at least six months to a year away (if not more) but that doesn\u2019t mean they can\u2019t be used today. Although there is an overhead to using them now \u2013 with the work required to set up SystemJS, the module transpiler, or another solution \u2013 that doesn\u2019t mean it\u2019s not worthwhile. Using any module system in the browser, whether that be RequireJS, Browserify or another alternative, requires extra tooling and libraries to support it, and I would argue that the effort to set up SystemJS is no greater than that required to configure any other tool. It also comes with the extra benefit that when the syntax is supported in browsers, you get a free upgrade. You\u2019ll be able to remove SystemJS and have everything continue to work, backed by the native browser solution.\n\nIf you are starting a new project, I would strongly advocate using ES6 modules. It is a syntax and specification that is not going away at all, and will soon be supported in browsers. Investing time in learning it now will pay off hugely further down the road.\n\nFurther reading\n\nIf you\u2019d like to delve further into ES6 modules (or ES6 generally) and using them today, I recommend the following resources:\n\n\n\tECMAScript 6 modules: the final syntax by Axel Rauschmayer\n\tPractical Workflows for ES6 Modules by Guy Bedford\n\tECMAScript 6 resources for the curious JavaScripter by Addy Osmani\n\tTracking ES6 support by Addy Osmani\n\tES6 Tools List by Addy Osmani\n\tUsing Grunt and the ES6 Module Transpiler by Thomas Boyt\n\tJavaScript Modules and Dependencies with jspm by myself\n\tUsing ES6 Modules Today by Guy Bedford", "year": "2014", "author": "Jack Franklin", "author_slug": "jackfranklin", "published": "2014-12-03T00:00:00+00:00", "url": "https://24ways.org/2014/javascript-modules-the-es6-way/", "topic": "code"}
{"rowid": 49, "title": "Universal React", "contents": "One of the libraries to receive a huge amount of focus in 2015 has been ReactJS, a library created by Facebook for building user interfaces and web applications.\nMore generally we\u2019ve seen an even greater rise in the number of applications built primarily on the client side with most of the logic implemented in JavaScript. One of the main issues with building an app in this way is that you immediately forgo any customers who might browse with JavaScript turned off, and you can also miss out on any robots that might visit your site to crawl it (such as Google\u2019s search bots). Additionally, we gain a performance improvement by being able to render from the server rather than having to wait for all the JavaScript to be loaded and executed.\nThe good news is that this problem has been recognised and it is possible to build a fully featured client-side application that can be rendered on the server. The way in which these apps work is as follows:\n\nThe user visits www.yoursite.com and the server executes your JavaScript to generate the HTML it needs to render the page.\nIn the background, the client-side JavaScript is executed and takes over the duty of rendering the page.\nThe next time a user clicks, rather than being sent to the server, the client-side app is in control.\nIf the user doesn\u2019t have JavaScript enabled, each click on a link goes to the server and they get the server-rendered content again.\n\nThis means you can still provide a very quick and snappy experience for JavaScript users without having to abandon your non-JS users. We achieve this by writing JavaScript that can be executed on the server or on the client (you might have heard this referred to as isomorphic) and using a JavaScript framework that\u2019s clever enough handle server- or client-side execution. Currently, ReactJS is leading the way here, although Ember and Angular are both working on solutions to this problem.\nIt\u2019s worth noting that this tutorial assumes some familiarity with React in general, its syntax and concepts. If you\u2019d like a refresher, the ReactJS docs are a good place to start.\n\u00a0Getting started\nWe\u2019re going to create a tiny ReactJS application that will work on the server and the client. First we\u2019ll need to create a new project and install some dependencies. In a new, blank directory, run:\nnpm init -y\nnpm install --save ejs express react react-router react-dom\nThat will create a new project and install our dependencies:\n\nejs is a templating engine that we\u2019ll use to render our HTML on the server.\nexpress is a small web framework we\u2019ll run our server on.\nreact-router is a popular routing solution for React so our app can fully support and respect URLs.\nreact-dom is a small React library used for rendering React components.\n\nWe\u2019re also going to write all our code in ECMAScript 6, and therefore need to install BabelJS and configure that too.\nnpm install --save-dev babel-cli babel-preset-es2015 babel-preset-react\nThen, create a .babelrc file that contains the following:\n{\n  \"presets\": [\"es2015\", \"react\"]\n}\nWhat we\u2019ve done here is install Babel\u2019s command line interface (CLI) tool and configured it to transform our code from ECMAScript 6 (or ES2015) to ECMAScript 5, which is more widely supported. We\u2019ll need the React transforms when we start writing JSX when working with React.\nCreating a server\nFor now, our ExpressJS server is pretty straightforward. All we\u2019ll do is render a view that says \u2018Hello World\u2019. Here\u2019s our server code:\nimport express from 'express';\nimport http from 'http';\n\nconst app = express();\n\napp.use(express.static('public'));\n\napp.set('view engine', 'ejs');\n\napp.get('*', (req, res) => {\n  res.render('index');\n});\n\nconst server = http.createServer(app);\n\nserver.listen(3003);\nserver.on('listening', () => {\n  console.log('Listening on 3003');\n});\nHere we\u2019re using ES6 modules, which I wrote about on 24 ways last year, if you\u2019d like a reminder. We tell the app to render the index view on any GET request (that\u2019s what app.get('*') means, the wildcard matches any route).\nWe now need to create the index view file, which Express expects to be defined in views/index.ejs:\n<!DOCTYPE html>\n<html>\n  <head>\n    <title>My App</title>\n  </head>\n\n  <body>\n    Hello World\n  </body>\n</html>\nFinally, we\u2019re ready to run the server. Because we installed babel-cli earlier we have access to the babel-node executable, which will transform all your code before running it through node. Run this command:\n./node_modules/.bin/babel-node server.js\nAnd you should now be able to visit http://localhost:3003 and see \u2018Hello World\u2019 right there:\n\nBuilding the React app\nNow we\u2019ll build the React application entirely on the server, before adding the client-side JavaScript right at the end. Our app will have two routes, / and /about which will both show a small amount of content. This will demonstrate how to use React Router on the server side to make sure our React app plays nicely with URLs.\nFirstly, let\u2019s update views/index.ejs. Our server will figure out what HTML it needs to render, and pass that into the view. We can pass a value into our view when we render it, and then use EJS syntax to tell it to output that data. Update the template file so the body looks like so:\n<body>\n  <%- markup %>\n</body>\nNext, we\u2019ll define the routes we want our app to have using React Router. For now we\u2019ll just define the index route, and not worry about the /about route quite yet. We could define our routes in JSX, but I think for server-side rendering it\u2019s clearer to define them as an object. Here\u2019s what we\u2019re starting with:\nconst routes = {\n  path: '',\n  component: AppComponent,\n  childRoutes: [\n    {\n      path: '/',\n      component: IndexComponent\n    }\n  ]\n}\nThese are just placed at the top of server.js, after the import statements. Later we\u2019ll move these into a separate file, but for now they are fine where they are.\nNotice how I define first that the AppComponent should be used at the '' path, which effectively means it matches every single route and becomes a container for all our other components. Then I give it a child route of /, which will match the IndexComponent. Before we hook these routes up with our server, let\u2019s quickly define components/app.js and components/index.js. app.js looks like so:\nimport React from 'react';\n\nexport default class AppComponent extends React.Component {\n  render() {\n    return (\n      <div>\n        <h2>Welcome to my App</h2>\n        { this.props.children }\n      </div>\n    );\n  }\n}\nWhen a React Router route has child components, they are given to us in the props under the children key, so we need to include them in the code we want to render for this component. The index.js component is pretty bland:\nimport React from 'react';\n\nexport default class IndexComponent extends React.Component {\n  render() {\n    return (\n      <div>\n        <p>This is the index page</p>\n      </div>\n    );\n  }\n}\nServer-side routing with React Router\nHead back into server.js, and firstly we\u2019ll need to add some new imports:\nimport React from 'react';\nimport { renderToString } from 'react-dom/server';\nimport { match, RoutingContext } from 'react-router';\n\nimport AppComponent from './components/app';\nimport IndexComponent from './components/index';\nThe ReactDOM package provides react-dom/server which includes a renderToString method that takes a React component and produces the HTML string output of the component. It\u2019s this method that we\u2019ll use to render the HTML from the server, generated by React. From the React Router package we use match, a function used to find a matching route for a URL; and RoutingContext, a React component provided by React Router that we\u2019ll need to render. This wraps up our components and provides some functionality that ties React Router together with our app. Generally you don\u2019t need to concern yourself about how this component works, so don\u2019t worry too much.\nNow for the good bit: we can update our app.get('*') route with the code that matches the URL against the React routes:\napp.get('*', (req, res) => {\n  // routes is our object of React routes defined above\n  match({ routes, location: req.url }, (err, redirectLocation, props) => {\n    if (err) {\n      // something went badly wrong, so 500 with a message\n      res.status(500).send(err.message);\n    } else if (redirectLocation) {\n      // we matched a ReactRouter redirect, so redirect from the server\n      res.redirect(302, redirectLocation.pathname + redirectLocation.search);\n    } else if (props) {\n      // if we got props, that means we found a valid component to render\n      // for the given route\n      const markup = renderToString(<RoutingContext {...props} />);\n\n      // render `index.ejs`, but pass in the markup we want it to display\n      res.render('index', { markup })\n\n    } else {\n      // no route match, so 404. In a real app you might render a custom\n      // 404 view here\n      res.sendStatus(404);\n    }\n  });\n});\nWe call match, giving it the routes object we defined earlier and req.url, which contains the URL of the request. It calls a callback function we give it, with err, redirectLocation and props as the arguments. The first two conditionals in the callback function just deal with an error occuring or a redirect (React Router has built in redirect support). The most interesting bit is the third conditional, else if (props). If we got given props and we\u2019ve made it this far it means we found a matching component to render and we can use this code to render it:\n...\n} else if (props) {\n  // if we got props, that means we found a valid component to render\n  // for the given route\n  const markup = renderToString(<RoutingContext {...props} />);\n\n  // render `index.ejs`, but pass in the markup we want it to display\n  res.render('index', { markup })\n} else {\n   ...\n}\nThe renderToString method from ReactDOM takes that RoutingContext component we mentioned earlier and renders it with the properties required. Again, you need not concern yourself with what this specific component does or what the props are. Most of this is data that React Router provides for us on top of our components.\nNote the {...props}, which is a neat bit of JSX syntax that spreads out our object into key value properties. To see this better, note the two pieces of JSX code below, both of which are equivalent:\n<MyComponent a=\"foo\" b=\"bar\" />\n\n// OR:\n\nconst props = { a: \"foo\", b: \"bar\" };\n<MyComponent {...props} />\nRunning the server again\nI know that felt like a lot of work, but the good news is that once you\u2019ve set this up you are free to focus on building your React components, safe in the knowledge that your server-side rendering is working. To check, restart the server and head to http://localhost:3003 once more. You should see it all working!\n\nRefactoring and one more route\nBefore we move on to getting this code running on the client, let\u2019s add one more route and do some tidying up. First, move our routes object out into routes.js:\nimport AppComponent from './components/app';\nimport IndexComponent from './components/index';\n\nconst routes = {\n  path: '',\n  component: AppComponent,\n  childRoutes: [\n    {\n      path: '/',\n      component: IndexComponent\n    }\n  ]\n}\n\nexport { routes };\nAnd then update server.js. You can remove the two component imports and replace them with:\nimport { routes } from './routes';\nFinally, let\u2019s add one more route for ./about and links between them. Create components/about.js:\nimport React from 'react';\n\nexport default class AboutComponent extends React.Component {\n  render() {\n    return (\n      <div>\n        <p>A little bit about me.</p>\n      </div>\n    );\n  }\n}\nAnd then you can add it to routes.js too:\nimport AppComponent from './components/app';\nimport IndexComponent from './components/index';\nimport AboutComponent from './components/about';\n\nconst routes = {\n  path: '',\n  component: AppComponent,\n  childRoutes: [\n    {\n      path: '/',\n      component: IndexComponent\n    },\n    {\n      path: '/about',\n      component: AboutComponent\n    }\n  ]\n}\n\nexport { routes };\nIf you now restart the server and head to http://localhost:3003/about` you\u2019ll see the about page!\n\nFor the finishing touch we\u2019ll use the React Router link component to add some links between the pages. Edit components/app.js to look like so:\nimport React from 'react';\nimport { Link } from 'react-router';\n\nexport default class AppComponent extends React.Component {\n  render() {\n    return (\n      <div>\n        <h2>Welcome to my App</h2>\n        <ul>\n          <li><Link to='/'>Home</Link></li>\n          <li><Link to='/about'>About</Link></li>\n        </ul>\n        { this.props.children }\n      </div>\n    );\n  }\n}\nYou can now click between the pages to navigate. However, everytime we do so the requests hit the server. Now we\u2019re going to make our final change, such that after the app has been rendered on the server once, it gets rendered and managed in the client, providing that snappy client-side app experience.\nClient-side rendering\nFirst, we\u2019re going to make a small change to views/index.ejs. React doesn\u2019t like rendering directly into the body and will give a warning when you do so. To prevent this we\u2019ll wrap our app in a div:\n<body>\n  <div id=\"app\"><%- markup %></div>\n  <script src=\"build.js\"></script>\n</body>\nI\u2019ve also added in a script tag to build.js, which is the file we\u2019ll generate containing all our client-side code.\nNext, create client-render.js. This is going to be the only bit of JavaScript that\u2019s exclusive to the client side. In it we need to pull in our routes and render them to the DOM.\nimport React from 'react';\nimport ReactDOM from 'react-dom';\nimport { Router } from 'react-router';\n\nimport { routes } from './routes';\n\nimport createBrowserHistory from 'history/lib/createBrowserHistory';\n\nReactDOM.render(\n  <Router routes={routes} history={createBrowserHistory()} />,\n  document.getElementById('app')\n)\nThe first thing you might notice is the mention of createBrowserHistory. React Router is built on top of the history module, a module that listens to the browser\u2019s address bar and parses the new location. It has many modes of operation: it can keep track using a hashbang, such as http://localhost/#!/about (this is the default), or you can tell it to use the HTML5 history API by calling createBrowserHistory, which is what we\u2019ve done. This will keep the URLs nice and neat and make sure the client and the server are using the same URL structure. You can read more about React Router and histories in the React Router documentation.\nFinally we use ReactDOM.render and give it the Router component, telling it about all our routes, and also tell ReactDOM where to render, the #app element.\nGenerating build.js\nWe\u2019re actually almost there! The final thing we need to do is generate our client side bundle. For this we\u2019re going to use webpack, a module bundler that can take our application, follow all the imports and generate one large bundle from them. We\u2019ll install it and babel-loader, a webpack plugin for transforming code through Babel.\nnpm install --save-dev webpack babel-loader\nTo run webpack we just need to create a configuration file, called webpack.config.js. Create the file in the root of our application and add the following code:\nvar path = require('path');\nmodule.exports = {\n  entry: path.join(process.cwd(), 'client-render.js'),\n  output: {\n    path: './public/',\n    filename: 'build.js'\n  },\n  module: {\n    loaders: [\n      {\n        test: /.js$/,\n        loader: 'babel'\n      }\n    ]\n  }\n}\nNote first that this file can\u2019t be written in ES6 as it doesn\u2019t get transformed. The first thing we do is tell webpack the main entry point for our application, which is client-render.js. We use process.cwd() because webpack expects an exact location \u2013 if we just gave it the string \u2018client-render.js\u2019, webpack wouldn\u2019t be able to find it.\nNext, we tell webpack where to output our file, and here I\u2019m telling it to place the file in public/build.js. Finally we tell webpack that every time it hits a file that ends in .js, it should use the babel-loader plugin to transform the code first.\nNow we\u2019re ready to generate the bundle!\n./node_modules/.bin/webpack\nThis will take a fair few seconds to run (on my machine it\u2019s about seven or eight), but once it has it will have created public/build.js, a client-side bundle of our application. If you restart your server once more you\u2019ll see that we can now navigate around our application without hitting the server, because React on the client takes over. Perfect!\nThe first bundle that webpack generates is pretty slow, but if you run webpack -w it will go into watch mode, where it watches files for changes and regenerates the bundle. The key thing is that it only regenerates the small pieces of the bundle it needs, so while the first bundle is very slow, the rest are lightning fast. I recommend leaving webpack constantly running in watch mode when you\u2019re developing.\nConclusions\nFirst, if you\u2019d like to look through this code yourself you can find it all on GitHub. Feel free to raise an issue there or tweet me if you have any problems or would like to ask further questions.\nNext, I want to stress that you shouldn\u2019t use this as an excuse to build all your apps in this way. Some of you might be wondering whether a static site like the one we built today is worth its complexity, and you\u2019d be right. I used it as it\u2019s an easy example to work with but in the future you should carefully consider your reasons for wanting to build a universal React application and make sure it\u2019s a suitable infrastructure for you.\nWith that, all that\u2019s left for me to do is wish you a very merry Christmas and best of luck with your React applications!", "year": "2015", "author": "Jack Franklin", "author_slug": "jackfranklin", "published": "2015-12-05T00:00:00+00:00", "url": "https://24ways.org/2015/universal-react/", "topic": "code"}