root routeReact.lazy and React.Suspenselinks exports<head>Millions of React applications deployed worldwide are powered by React Router. Chances are you've shipped a few of them! Because Remix is built on top of React Router, we have worked to make migration an easy process you can work through iteratively to avoid huge refactors.
If you aren't already using React Router, we think there are several compelling reasons to reconsider! History management, dynamic path matching, nested routing, and much more. Take a look at the React Router docs and see all what we have to offer.
If you are using an older version of React Router, the first step is to upgrade to v6. Check out the migration guide from v5 to v6 and our backwards compatibility package to upgrade your app to v6 quickly and iteratively.
First, you'll need a few of our packages to build on Remix. Follow the instructions below, running all commands from the root of your project.
npm install @remix-run/react @remix-run/node @remix-run/serve
npm install -D @remix-run/dev
Most React Router apps run primarily in the browser. The server's only job is to send a single static HTML page while React Router manages the route-based views client-side. These apps generally have a browser entrypoint file like a root index.js that looks something like this:
import * as ReactDOM from "react-dom";
import App from "./App";
ReactDOM.render(<App />, document.getElementById("app"));
Server-rendered React apps are a little different. The browser script is not rendering your app, but is "hydrating" the DOM provided by the server. Hydration is the process of mapping the elements in the DOM to their React component counterparts and setting up event listeners so that your app is interactive.
Let's start by creating two new files:
app/entry.server.jsx (or entry.server.tsx)app/entry.client.jsx (or entry.client.tsx)app directory by convention. If your existing app uses a directory with the same name, rename it to something like src or old-app to differentiate as we migrate to Remix.
import { RemixServer } from "@remix-run/react";
import { renderToString } from "react-dom/server";
export default function handleRequest(
request,
responseStatusCode,
responseHeaders,
remixContext
) {
let markup = renderToString(
<RemixServer context={remixContext} url={request.url} />
);
responseHeaders.set("Content-Type", "text/html");
return new Response("<!DOCTYPE html>" + markup, {
status: responseStatusCode,
headers: responseHeaders,
});
}
If you are using React 17, your client entrypoint will look like this:
import { RemixBrowser } from "@remix-run/react";
import { hydrate } from "react-dom";
hydrate(<RemixBrowser />, document);
In React 18, you'll use hydrateRoot instead of hydrate.
import { RemixBrowser } from "@remix-run/react";
import { hydrateRoot } from "react-dom/client";
hydrateRoot(document, <RemixBrowser />);
root routeWe mentioned that Remix is built on top of React Router. Your app likely renders a BrowserRouter with your routes defined in JSX Route components. We don't need to do that in Remix, but more on that later. For now we need to provide the lowest level route our Remix app needs to work.
The root route (or the "root root" if you're Wes Bos) is responsible for providing the structure of the application. Its default export is a component that renders the full HTML tree that every other route loads and depends on. Think of it as the scaffold or shell of your app.
In a client-rendered app, you will have an index HTML file that includes the DOM node for mounting your React app. The root route will render markup that mirrors the structure of this file.
Create a new file called root.jsx (or root.tsx) in your app directory. The contents of that file will vary, but let's assume that your index.html looks something like this:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<link rel="icon" href="/favicon.ico" />
<meta
name="viewport"
content="width=device-width, initial-scale=1"
/>
<meta name="theme-color" content="#000000" />
<meta
name="description"
content="My beautiful React app"
/>
<link rel="apple-touch-icon" href="/logo192.png" />
<link rel="manifest" href="/manifest.json" />
<title>My React App</title>
</head>
<body>
<noscript
>You need to enable JavaScript to run this
app.</noscript
>
<div id="root"></div>
</body>
</html>
In your root.jsx, export a component that mirrors its structure:
import { Outlet } from "@remix-run/react";
export default function Root() {
return (
<html lang="en">
<head>
<meta charSet="utf-8" />
<link rel="icon" href="/favicon.ico" />
<meta
name="viewport"
content="width=device-width, initial-scale=1"
/>
<meta name="theme-color" content="#000000" />
<meta
name="description"
content="My beautiful React app"
/>
<link rel="apple-touch-icon" href="/logo192.png" />
<link rel="manifest" href="/manifest.json" />
<title>My React App</title>
</head>
<body>
<div id="root">
<Outlet />
</div>
</body>
</html>
);
}
Notice a few things here:
noscript tag. We're server rendering now, which means users who disable JavaScript will still be able to see our app (and over time, as you make a few tweaks to improve progressive enhancement, much of your app should still work).Outlet component from @remix-run/react. This is the same component that you would normally use to render your matched route in a React Router app; it serves the same function here, but it's adapted for the router in Remix.index.html from your public directory after you've created your root route. Keeping the file around may cause your server to send that HTML instead of your Remix app when accessing the / route.
First, move the root of your existing React code into your app directory. So if your root app code lives in an src directory in the project root, it should now be in app/src.
We also suggest renaming this directory to make it clear that this is your old code so that, eventually, you can delete it after migrating all of its contents. The beauty of this approach is that you don't have to do it all at once for your app to run as usual. In our demo project we name this directory old-app.
Lastly, in your root App component (the one that would have been mounted to the root element), remove the <BrowserRouter> from React Router. Remix takes care of this for you without needing to render the provider directly.
Remix needs routes beyond the root route to know what to render in <Outlet />. Fortunately you already render <Route> components in your app, and Remix can use those as you migrate to use our routing conventions.
To start, create a new directory in app called routes. In that directory, create a file called $.jsx. This is called a catch-all route and it will be useful to let your old app handle routes that you haven't moved into the routes directory yet.
Inside of your $.jsx file, all we need to do is export the code from our old root App:
export { default } from "~/old-app/app";
Remix provides its own bundler and CLI tools for development and building your app. Chances are your app used something like Create React App to bootstrap, or perhaps you have a custom build set up with Webpack.
In your package.json file, update your scripts to use remix commands instead of your current build and dev scripts.
{
"scripts": {
"build": "remix build",
"dev": "remix dev",
"start": "remix-serve build"
}
}
And poof! Your app is now server-rendered and your build went from 90 seconds to 0.5 seconds ⚡
Over time you'll want to migrate the routes rendered by React Router's <Route> components into their own route files. The filenames and directory structure outlined in our routing conventions will guide this migration.
The default export in your route file is the component rendered in the <Outlet />. So if you have a route in your App that looks like this:
function About() {
return (
<main>
<h1>About us</h1>
<PageContent />
</main>
);
}
function App() {
return (
<Routes>
<Route path="/about" element={<About />} />
</Routes>
);
}
Your route file should look like this:
export default function About() {
return (
<main>
<h1>About us</h1>
<PageContent />
</main>
);
}
Once you create this file, you can delete the <Route> component from your App. After all of your routes have been migrated you can delete <Routes> and ultimately all of the code in old-app.
At this point you might be able to say you are done with the initial migration. Congrats! However Remix does things a bit differently than your typical React app. If it didn't, why would we have bothered building it in the first place? 😅
A common pain-point in migrating a client-rendered codebase to a server-rendered one is that you may have references to browser APIs in code that runs on the server. A common example can be found when initializing values in state:
function Count() {
let [count, setCount] = React.useState(
() => localStorage.getItem("count") || 0
);
React.useEffect(() => {
localStorage.setItem("count", count);
}, [count]);
return (
<div>
<h1>Count: {count}</h1>
<button onClick={() => setCount(count + 1)}>
Increment
</button>
</div>
);
}
In this example, localStorage is used as a global store to persist some data across page reloads. We update localStorage with the current value of count in useEffect, which is perfectly safe because useEffect is only ever called in the browser! However initializing state based on localStorage is a problem, as this callback is executed on both the server and in the browser.
Your go-to solution may be to check for the window object and only run the callback in the browser. However this can lead to another problem, which is the dreaded hydration mismatch. React relies on markup rendered by the server to be identical to what is rendered during client hydration. This ensures that react-dom knows how to match DOM elements with their corresponding React components so that it can attach event listeners and perform updates as state changes. So if local storage gives us a different value than whatever we initiate on the server, we'll have a new problem to deal with.
One potential solution here is using a different caching mechanism that can be used on the server and passed to the component via props passed from a route's loader data. But if it isn't crucial for your app to render the component on the server, a simpler solution may be to skip rendering altogether on the server and wait until hydration is complete to render it in the browser.
// We can safely track hydration in memory state
// outside of the component because it is only
// updated once after the version instance of
// `SomeComponent` has been hydrated. From there,
// the browser takes over rendering duties across
// route changes and we no longer need to worry
// about hydration mismatches until the page is
// reloaded and `isHydrating` is reset to true.
let isHydrating = true;
function SomeComponent() {
let [isHydrated, setIsHydrated] = React.useState(
!isHydrating
);
React.useEffect(() => {
isHydrating = false;
setIsHydrated(true);
}, []);
if (isHydrated) {
return <Count />;
} else {
return <SomeFallbackComponent />;
}
}
To simplify this solution, we recommend the using the ClientOnly component in the remix-utils community package. An example of its usage can be found in the examples repository.
React.lazy and React.SuspenseIf you are lazy-loading components with React.lazy and React.Suspense, you may run into issues depending on the version of React you are using. Until React 18, this would not work on the server as React.Suspense was originally implemented as a browser-only feature.
If you are using React 17, you have a few options:
React.lazy and React.Suspense altogetherKeep in mind that Remix automatically handles code-splitting for all your routes that it manages, so as you move things into the routes directory you should rarely—if ever—need to use React.lazy manually.
Further configuration is optional, but the following may be helpful to optimize your development workflow.
remix.config.jsEvery Remix app accepts a remix.config.js file in the project root. While its settings are optional, we recommend you include a few of them for clarity's sake. See the docs on configuration for more information about all available options.
/** @type {import('@remix-run/dev').AppConfig} */
module.exports = {
appDirectory: "app",
ignoredRouteFiles: ["**/.*"],
assetsBuildDirectory: "public/build",
};
jsconfig.json or tsconfig.jsonIf you are using TypeScript, you likely already have a tsconfig.json in your project. jsconfig.json is optional but provides helpful context for many editors. These are the minimal settings we recommend including in your language configuration.
/_appDirectory in your remix.config.js, you'll need to update your path alias for /_ as well.
{
"compilerOptions": {
"jsx": "react-jsx",
"resolveJsonModule": true,
"baseUrl": ".",
"paths": {
"~/*": ["./app/*"]
}
}
}
{
"include": ["remix.env.d.ts", "**/*.ts", "**/*.tsx"],
"compilerOptions": {
"lib": ["DOM", "DOM.Iterable", "ES2019"],
"isolatedModules": true,
"esModuleInterop": true,
"jsx": "react-jsx",
"resolveJsonModule": true,
"moduleResolution": "node",
"baseUrl": ".",
"noEmit": true,
"paths": {
"~/*": ["./app/*"]
}
}
}
If you are using TypeScript, you also need to create the remix.env.d.ts file in the root of your project with the appropriate global type references.
/// <reference types="@remix-run/dev" />
/// <reference types="@remix-run/node" />
At this point, you might be able to run your app with no changes. If you are using Create React App or a highly-configured Webpack app, you likely use import to include non-JavaScript modules like stylesheets and images.
Remix does not support most non-standard imports, and we think for good reason. Below is a non-exhaustive list of some of the differences you'll encounter in Remix, and how to refactor as you migrate.
Many bundlers use plugins to allow importing various assets like images and fonts. These typically come into your component as string representing the filepath of the asset.
import logo from "./logo.png";
export function Logo() {
return <img src={logo} alt="My logo" />;
}
In Remix, this works basically the same way. For assets like fonts that are loaded by a <link> element, you'll generally import these in a route module and include the filename in an object returned by a links function. See our docs on route links for more information.
Create React App and some Webpack plugins allow you to import SVG files as a React component. This is a common use case for SVG files, but it's not supported by default in Remix.
// This will not work in Remix!
import MyLogo from "./logo.svg";
export function Logo() {
return <MyLogo />;
}
If you want to use SVG files as React components, you'll need to first create the components and import them directly. React SVGR is a great toolset that can help you generate these components from the command line or in an online playground if you prefer to copy and paste.
<svg xmlns="http://www.w3.org/2000/svg" class="icon" viewBox="0 0 20 20" fill="currentColor">
<path fill-rule="evenodd" clip-rule="evenodd" d="M10 18a8 8 0 100-16 8 8 0 000 16zm3.707-8.707l-3-3a1 1 0 00-1.414 0l-3 3a1 1 0 001.414 1.414L9 9.414V13a1 1 0 102 0V9.414l1.293 1.293a1 1 0 001.414-1.414z" />
</svg>
export default function Icon() {
return (
<svg
xmlns="http://www.w3.org/2000/svg"
className="icon"
viewBox="0 0 20 20"
fill="currentColor"
>
<path
fillRule="evenodd"
clipRule="evenodd"
d="M10 18a8 8 0 100-16 8 8 0 000 16zm3.707-8.707l-3-3a1 1 0 00-1.414 0l-3 3a1 1 0 001.414 1.414L9 9.414V13a1 1 0 102 0V9.414l1.293 1.293a1 1 0 001.414-1.414z"
/>
</svg>
);
}
Create React App and many Webpack plugins support importing CSS in your components in many ways. While this is common practice in the React ecosystem, it's not supported the same way in Remix for a few different reasons. We'll discuss this in depth in the next section, but for now just know that you need to import your stylesheets in route modules. Importing stylesheets directly in non-route components is not currently supported.
Read more about route styles and why Remix does things a bit differently.
Let's talk a bit more about styles. Remix does not handle CSS imports the same way your bundler likely does, and we think that's for a good reason.
Assume you have a plain CSS import in your App component:
import { Outlet } from "react-router-dom";
import Logo from "./logo";
import SiteNav from "./site-nav";
import "./styles.css";
export default function App() {
return (
<div>
<header>
<Logo />
<SiteNav />
</header>
<main>
<Outlet />
</main>
<footer>© Remix Software</footer>
</div>
);
}
While this is a convenient API, consider a few questions:
<link /> or an inline <style /> in the <head>?The answer to all of these questions is up to your bundler, not you. We think there's a better way, and it's one that happens to be as old as HTML2: <link rel="stylesheet" />.
Note: Remix does not currently support CSS processing directly. If you use preprocessors like Sass, Less, or PostCSS, you can run those as a separate process in development.
We do process CSS Modules, but support is currently opt-in behind a feature flag.
links exportsIn Remix, stylesheets can only be loaded from route component files. Importing them does not do anything magical with your styles, rather it returns a URL that can be used to load the stylesheet as you see fit. You can render the stylesheet directly in your component or use our links export.
Let's move our app's stylesheet and a few other assets to the links function in our root route:
import { Links } from "@remix-run/react";
import App from "./app";
import stylesheetUrl from "./styles.css";
export function links() {
// `links` returns an array of objects whose
// properties map to the `<link />` component props
return [
{ rel: "icon", href: "/favicon.ico" },
{ rel: "apple-touch-icon", href: "/logo192.png" },
{ rel: "manifest", href: "/manifest.json" },
{ rel: "stylesheet", href: stylesheetUrl },
];
}
export default function Root() {
return (
<html lang="en">
<head>
<meta charSet="utf-8" />
<meta
name="viewport"
content="width=device-width, initial-scale=1"
/>
<meta name="theme-color" content="#000000" />
<meta
name="description"
content="Web site created using create-react-app"
/>
<Links />
<title>React App</title>
</head>
<body>
<App />
</body>
</html>
);
}
You'll notice on line 32 that we've rendered a <Links /> component that replaced all of our individual <link /> components. This is inconsequential if we only ever use links in the root route, but all child routes may export their own links that will also be rendered here. The links function can also return a PageLinkDescriptor object that allows you to prefetch the resources for a page the user is likely to navigate to.
If you currently inject <link /> tags into your page client-side in your existing route components, either directly or via an abstraction like react-helmet, you can stop doing that and instead use the links export. You get to delete a lot of code and possibly a dependency or two!
<head>Just as a <link> is rendered inside your route component and ultimately rendered in your root <Links /> component, your app may use some injection trickery to render additional components in the document <head>. Often this is done to change the document's <title> or <meta> tags.
Similar to links, each route can also export a meta function that—you guessed it—returns a value responsible for rendering <meta> tags for that route. This is useful because each route often has its own.
The API is slightly different for meta. Instead of an array, it returns an object where the keys represent the meta name attribute (or property in the case of OpenGraph tags) and the value is the content attribute. The object can also accept a title property that renders a <title /> component specifically for that route.
export function meta() {
return {
title: "About Us",
"og:title": "About Us",
description: "Doin hoodrat stuff with our friends",
"og:description": "Doin hoodrat stuff with our friends",
"og:image:url": "https://remix.run/og-image.png",
"og:image:alt": "Just doin a bunch of hoodrat stuff",
};
}
export default function About() {
return (
<main>
<h1>About us</h1>
<PageContent />
</main>
);
}
Again—no more weird dances to get meta into your routes from deep in the component tree. Export them at the route level and let the server handle it. ✨
Remix re-exports everything you get from react-router-dom and we recommend that you update your imports to get those modules from @remix-run/react. In many cases, those components are wrapped with additional functionality and features specifically optimized for Remix.
Before:
import { Link, Outlet } from "react-router-dom";
After:
import { Link, Outlet } from "@remix-run/react";
While we've done our best to provide a comprehensive migration guide, it's important to note that we built Remix from the ground up with a few key principles that differ significantly from how many React apps are currently built. While your app will likely run at this point, as you dig through our docs and explore our APIs, we think you'll be able to drastically reduce the complexity of your code and improve the end-user experience of your app. It might take a bit of time to get there, but you can eat that elephant one bite at a time.
Now then, go off and remix your app. We think you'll like what you build along the way! 💿
