\n\nSo you've got your React app, you're bundling it with Webpack, and things are\ngoing smooth. But then one day you notice your app's bundle is getting so big\nthat it's slowing things down.\n\nIt's time to start code-splitting your app!\n\n\n\nCode-splitting is the process of taking one large bundle containing your entire\napp, and splitting them up into multiple smaller bundles which contain separate\nparts of your app.\n\nThis might seem difficult to do, but tools like Webpack have this built in, and\nReact Loadable is designed to make it super simple.\n\n### Route-based splitting vs. Component-based splitting\n\nA common piece of advice you will see is to break your app into separate routes\nand load each one asynchronously. This seems to work well enough for many apps–\nas a user, clicking a link and waiting for a page to load is a familiar\nexperience on the web.\n\nBut we can do better than that.\n\nUsing most routing tools for React, a route is simply a component. There's\nnothing particularly special about them (Sorry Ryan and Michael– you're what's\nspecial). So what if we optimized for splitting around components instead of\nroutes? What would that get us?\n\n\n\nAs it turns out: Quite a lot. There are many more places than just routes where\nyou can pretty easily split apart your app. Modals, tabs, and many more UI\ncomponents hide content until the user has done something to reveal it.\n\n> **Example:** Maybe your app has a map buried inside of a tab component. Why\n> would you load a massive mapping library for the parent route every time when\n> the user may never go to that tab?\n\nNot to mention all the places where you can defer loading content until higher\npriority content is finished loading. That component at the bottom of your page\nwhich loads a bunch of libraries: Why should that be loaded at the same time as\nthe content at the top?\n\nAnd because routes are just components, we can still easily code-split at the\nroute level.\n\nIntroducing new code-splitting points in your app should be so easy that you\ndon't think twice about it. It should be a matter of changing a few lines of\ncode and everything else should be automated.\n\n### Introducing React Loadable\n\nReact Loadable is a small library that makes component-centric code splitting\nincredibly easy in React.\n\n`Loadable` is a higher-order component (a function that creates a component)\nwhich lets you dynamically load any module before rendering it into your app.\n\nLet's imagine two components, one that imports and renders another.\n\n```js\nimport Bar from './components/Bar';\n\nclass Foo extends React.Component {\n render() {\n return ;\n }\n}\n```\n\nRight now we're depending on `Bar` being imported synchronously via `import`,\nbut we don't need it until we go to render it. So why don't we just defer that?\n\nUsing a **dynamic import** ([a tc39 proposal currently at Stage 3](https://github.com/tc39/proposal-dynamic-import))\nwe can modify our component to load `Bar` asynchronously.\n\n```js\nclass MyComponent extends React.Component {\n state = {\n Bar: null\n };\n\n componentWillMount() {\n import('./components/Bar').then(Bar => {\n this.setState({ Bar });\n });\n }\n\n render() {\n let {Bar} = this.state;\n if (!Bar) {\n return
Loading...
;\n } else {\n return ;\n };\n }\n}\n```\n\nBut that's a whole bunch of work, and it doesn't even handle a bunch of cases.\nWhat about when `import()` fails? What about server-side rendering?\n\nInstead you can use `Loadable` to abstract away the problem.\n\n```js\nimport Loadable from 'react-loadable';\n\nconst LoadableBar = Loadable({\n loader: () => import('./components/Bar'),\n loading() {\n return
Loading...
\n }\n});\n\nclass MyComponent extends React.Component {\n render() {\n return ;\n }\n}\n```\n\n### Automatic code-splitting on `import()`\n\nWhen you use `import()` with Webpack 2+, it will\n[automatically code-split](https://webpack.js.org/guides/code-splitting/) for\nyou with no additional configuration.\n\nThis means that you can easily experiment with new code splitting points just\nby switching to `import()` and using React Loadable. Figure out what performs\nbest for your app.\n\n### Creating a great \"Loading...\" Component\n\nRendering a static \"Loading...\" doesn't communicate enough to the user. You\nalso need to think about error states, timeouts, and making it a nice\nexperience.\n\n```js\nfunction Loading() {\n return
Loading...
;\n}\n\nLoadable({\n loader: () => import('./WillFailToLoad'), // oh no!\n loading: Loading,\n});\n```\n\nTo make this all nice, your [loading component](#loadingcomponent) receives a\ncouple different props.\n\n#### Loading error states\n\nWhen your [`loader`](optsloader) fails, your [loading component](#loadingcomponent)\nwill receive an [`error`](propserror) prop which will be an `Error` object (otherwise it\nwill be `null`).\n\n```js\nfunction Loading(props) {\n if (props.error) {\n return
Error!
;\n } else {\n return
Loading...
;\n }\n}\n```\n\n#### Avoiding _Flash Of Loading Component_\n\nSometimes components load really quickly (<200ms) and the loading screen only\nquickly flashes on the screen.\n\nA number of user studies have proven that this causes users to perceive things\ntaking longer than they really have. If you don't show anything, users perceive\nit as being faster.\n\nSo your loading component will also get a [`pastDelay` prop](#propspastdelay)\nwhich will only be true once the component has taken longer to load than a set\n[delay](#optsdelay).\n\n```js\nfunction Loading(props) {\n if (props.error) {\n return
Error!
;\n } else if (props.pastDelay) {\n return
Loading...
;\n } else {\n return null;\n }\n}\n```\n\nThis delay defaults to `200ms` but you can also customize the\n[delay](#optsdelay) in `Loadable`.\n\n```js\nLoadable({\n loader: () => import('./components/Bar'),\n loading: Loading,\n delay: 300, // 0.3 seconds\n});\n```\n\n#### Timing out when the `loader` is taking too long\n\nSometimes network connections suck and never resolve or fail, they just hang\nthere forever. This sucks for the user because they won't know if it should\nalways take this long, or if they should try refreshing.\n\nThe [loading component](#loadingcomponent) will receive a\n[`timedOut` prop](#propstimedout) which will be set to `true` when the\n[`loader`](#optsloader) has timed out.\n\n```js\nfunction Loading(props) {\n if (props.error) {\n return
Error!
;\n } else if (props.timedOut) {\n return
Taking a long time...
;\n } else if (props.pastDelay) {\n return
Loading...
;\n } else {\n return null;\n }\n}\n```\n\nHowever, this feature is disabled by default. To turn it on, you can pass a\n[`timeout` option](#optstimeout) to `Loadable`.\n\n```js\nLoadable({\n loader: () => import('./components/Bar'),\n loading: Loading,\n timeout: 10000, // 10 seconds\n});\n```\n\n### Customizing rendering\n\nBy default `Loadable` will render the `default` export of the returned module.\nIf you want to customize this behavior you can use the\n[`render` option](#optsrender).\n\n```js\nLoadable({\n loader: () => import('./my-component'),\n render(loaded, props) {\n let Component = loaded.namedExport;\n return ;\n }\n});\n```\n\n### Loading multiple resources\n\nTechnically you can do whatever you want within `loader()` as long as it\nreturns a promise and [you're able to render something](#customizing-rendering).\nBut writing it out can be a bit annoying.\n\nTo make it easier to load multiple resources in parallel, you can use\n[`Loadable.Map`](#loadablemap).\n\n```js\nLoadable.Map({\n loader: {\n Bar: () => import('./Bar'),\n i18n: () => fetch('./i18n/bar.json').then(res => res.json()),\n },\n render(loaded, props) {\n let Bar = loaded.Bar.default;\n let i18n = loaded.i18n;\n return ;\n },\n});\n```\n\nWhen using `Loadable.Map` the [`render()` method](#optsrender) is required. It\nwill be passed a `loaded` param which will be an object matching the shape of\nyour `loader`.\n\n### Preloading\n\nAs an optimization, you can also decide to preload a component before it gets\nrendered.\n\nFor example, if you need to load a new component when a button gets pressed,\nyou could start preloading the component when the user hovers over the button.\n\nThe component created by `Loadable` exposes a\n[static `preload` method](#loadablecomponentpreload) which does exactly this.\n\n```js\nconst LoadableBar = Loadable({\n loader: () => import('./Bar'),\n loading: Loading,\n});\n\nclass MyComponent extends React.Component {\n state = { showBar: false };\n\n onClick = () => {\n this.setState({ showBar: true });\n };\n\n onMouseOver = () => {\n LoadableBar.preload();\n };\n\n render() {\n return (\n
\n \n Show Bar\n \n {this.state.showBar && }\n
\n )\n }\n}\n```\n\n
\n \n \n \n \n \n Server-Side Rendering\n
\n\nWhen you go to render all these dynamically loaded components, what you'll get\nis a whole bunch of loading screens.\n\nThis really sucks, but the good news is that React Loadable is designed to\nmake server-side rendering work as if nothing is being loaded dynamically.\n\nHere's our starting server using [Express](https://expressjs.com/).\n\n```js\nimport express from 'express';\nimport React from 'react';\nimport ReactDOMServer from 'react-dom/server';\nimport App from './components/App';\n\nconst app = express();\n\napp.get('/', (req, res) => {\n res.send(`\n \n \n ...\n \n
${ReactDOMServer.renderToString()}
\n \n \n \n `);\n});\n\napp.listen(3000, () => {\n console.log('Running on http://localhost:3000/');\n});\n```\n\n### Preloading all your loadable components on the server\n\nThe first step to rendering the correct content from the server is to make sure\nthat all of your loadable components are already loaded when you go to render\nthem.\n\nTo do this, you can use the [`Loadable.preloadAll`](#loadablepreloadall)\nmethod. It returns a promise that will resolve when all your loadable\ncomponents are ready.\n\n```js\nLoadable.preloadAll().then(() => {\n app.listen(3000, () => {\n console.log('Running on http://localhost:3000/');\n });\n});\n```\n\n### Picking up a server-side rendered app on the client\n\nThis is where things get a little bit tricky. So let's prepare ourselves\nlittle bit.\n\nIn order for us to pick up what was rendered from the server we need to have\nall the same code that was used to render on the server.\n\nTo do this, we first need our loadable components telling us which modules they\nare rendering.\n\n#### Declaring which modules are being loaded\n\nThere are two options in [`Loadable`](#loadable) and\n[`Loadable.Map`](#loadablemap) which are used to tell us which modules our\ncomponent is trying to load: [`opts.modules`](#optsmodules) and\n[`opts.webpack`](#optswebpack).\n\n```js\nLoadable({\n loader: () => import('./Bar'),\n modules: ['./Bar'],\n webpack: () => [require.resolveWeak('./Bar')],\n});\n```\n\nBut don't worry too much about these options. React Loadable includes a\n[Babel plugin](#babel-plugin) to add them for you.\n\nJust add the `react-loadable/babel` plugin to your Babel config:\n\n```json\n{\n \"plugins\": [\n \"react-loadable/babel\"\n ]\n}\n```\n\nNow these options will automatically be provided.\n\n#### Finding out which dynamic modules were rendered\n\nNext we need to find out which modules were actually rendered when a request\ncomes in.\n\nFor this, there is [`Loadable.Capture`](#loadablecapture) component which can\nbe used to collect all the modules that were rendered.\n\n```js\nimport Loadable from 'react-loadable';\n\napp.get('/', (req, res) => {\n let modules = [];\n\n let html = ReactDOMServer.renderToString(\n modules.push(moduleName)}>\n \n \n );\n\n console.log(modules);\n\n res.send(`...${html}...`);\n});\n```\n\n#### Mapping loaded modules to bundles\n\nIn order to make sure that the client loads all the modules that were rendered\nserver-side, we'll need to map them to the bundles that Webpack created.\n\nThis comes in two parts.\n\nFirst we need Webpack to tell us which bundles each module lives inside. For\nthis there is the [React Loadable Webpack plugin](#webpack-plugin).\n\nImport the `ReactLoadablePlugin` from `react-loadable/webpack` and include it\nin your webpack config. Pass it a `filename` for where to store the JSON data\nabout our bundles.\n\n```js\n// webpack.config.js\nimport { ReactLoadablePlugin } from 'react-loadable/webpack';\n\nexport default {\n plugins: [\n new ReactLoadablePlugin({\n filename: './dist/react-loadable.json',\n }),\n ],\n};\n```\n\nThen we'll go back to our server and use this data to convert our modules to\nbundles.\n\nTo convert from modules to bundles, import the [`getBundles`](#getbundles)\nmethod from `react-loadable/webpack` and the data from Webpack.\n\n```js\nimport Loadable from 'react-loadable';\nimport { getBundles } from 'react-loadable/webpack'\nimport stats from './dist/react-loadable.json';\n\napp.get('/', (req, res) => {\n let modules = [];\n\n let html = ReactDOMServer.renderToString(\n modules.push(moduleName)}>\n \n \n );\n\n let bundles = getBundles(stats, modules);\n\n // ...\n});\n```\n\nWe can then render these bundles into `\n ${bundles.map(bundle => {\n return ``\n // alternatively if you are using publicPath option in webpack config\n // you can use the publicPath value from bundle, e.g:\n // return ``\n }).join('\\n')}\n \n
![\"GUIDE\"](\"http://thejameskyle.com/img/react-loadable-guide.png\")
\n ![\"SERVER](\"http://thejameskyle.com/img/react-loadable-ssr.png\")
\n