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description
Migration guide for Fresh 2.x

We tried to keep breaking changes in Fresh 2 as minimal as possible, but some changes need to be updated manually. Fresh 2 comes with many quality of life improvements that make it easier to extend and adapt Fresh. We've created this upgrade guide as part of upgrading our own apps here at Deno.

Use this guide to migrate a Fresh 1.x app to Fresh 2.

Applying automatic updates

Most changes can be applied automatically with the update script. Start the update by running it in your project directory:

deno run -Ar jsr:@fresh/update

This will apply most API changes made in Fresh 2 automatically update like changing $fresh/server.ts imports to fresh.

Getting main.ts and dev.ts ready

Configuring Fresh doesn't require a dedicated config file anymore. You can delete the fresh.config.ts file. The fresh.gen.ts manifest file isn't needed anymore either.

  routes/
  dev.ts
- fresh.gen.ts
- fresh.config.ts
  main.ts

Fresh 2 takes great care in ensuring that code that's only needed during development is separate from production code. This split makes deployments much smaller, quicker to upload and allows them to boot up much quicker in production.

Updating dev.ts

Development related configuration can be passed to the Builder class instance in dev.ts. This file is also where you typically set up development-only plugins like tailwindcss.

The full dev.ts file for newly generated Fresh 2 projects looks like this:

import { Builder } from "fresh/dev";
import { tailwind } from "@fresh/plugin-tailwind";

// Pass development only configuration here
const builder = new Builder({ target: "safari12" });

// Example: Enabling the tailwind plugin for Fresh
tailwind(builder);

// Create optimized assets for the browser when
// running `deno run -A dev.ts build`
if (Deno.args.includes("build")) {
  await builder.build();
} else {
  // ...otherwise start the development server
  await builder.listen(() => import("./main.ts"));
}

Updating main.ts

Similarly, configuration related to running Fresh in production can be passed to new App():

// main.ts
import { App, fsRoutes, staticFiles } from "fresh";

export const app = new App()
  // Add static file serving middleware
  .use(staticFiles())
  // Enable file-system based routing
  .fsRoutes();

Merging error pages

Both the _500.tsx and _404.tsx template have been unified into a single _error.tsx template.

  routes/
-   ├── _404.tsx
-   ├── _500.tsx
+   ├── _error.tsx
    └── ...

Inside the _error.tsx template you can show different content based on errors or status codes with the following code:

export default function ErrorPage(props: PageProps) {
  const error = props.error; // Contains the thrown Error or HTTPError
  if (error instanceof HttpError) {
    const status = error.status; // HTTP status code

    // Render a 404 not found page
    if (status === 404) {
      return <h1>404 - Page not found</h1>;
    }
  }

  return <h1>Oh no...</h1>;
}

Removal of <Head> component

The <Head> component was used in Fresh 1.x to add additional tags to the <head> portion of an HTML document from anywhere on the page. This feature was removed in preparation and due to performance concerns as it required a complex machinery in the background to work.

Instead, passing head-related data is best done via ctx.state

// about.tsx
export const handler = {
  GET(ctx) {
    // Set a route specific data in a handler
    ctx.state.title = "About Me";
    return page();
  },
};

// Render that in _app.tsx
export default function AppWrapper(ctx: FreshContext) {
  return (
    <html lang="en">
      <head>
        <meta charset="utf-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        {ctx.state.title ? <title>{ctx.state.title}</title> : null}
      </head>
      <body>
        <ctx.Component />
      </body>
    </html>
  );
}

Update deployment settings

Fresh 2 requires assets to be build during deployment instead of building them on demand. Run the deno task build command as part of your deployment process. If you have already set up Fresh's 1.x "Ahead-of-Time Builds", then no changes are necessary.

Trailing slash handling

The handling trailing slashes has been extracted to an optional middleware that you can add if needed. This middleware can be used to ensure that URLs always have a trailing slash at the end or that they will never have one.

-  import { App, staticFiles } from "fresh";
+  import { App, staticFiles, trailingSlashes } from "fresh";

  export const app = new App({ root: import.meta.url })
    .use(staticFiles())
+   .use(trailingSlashes("never"));

Automatic updates

[info]: The changes listed here are applied automatically when running the @fresh/update script and you shouldn't need to have to do these yourself.

Unified middleware signatures

Middleware, handler and route component signatures have been unified to all look the same. Instead of receiving two arguments, they receive one. The Request object is stored on the context object as ctx.req.

- const middleware = (req, ctx) => new Response("ok");
+ const middleware = (ctx) => new Response("ok");

Same is true for handlers:

  export const handler = {
-   GET(req, ctx) {
+   GET(ctx) {
      return new Response("ok");
    },
  };

...and async route components:

-  export default async function MyPage(req: Request, ctx: RouteContext) {
+  export default async function MyPage(props: PageProps) {
    const value = await loadFooValue();
    return <p>foo is: {value}</p>;
  }

All the various context interfaces have been consolidated and simplified:

Fresh 1.x Fresh 2.x
AppContext, LayoutContext, RouteContext Context

Context methods

The ctx.renderNotFound() method has been removed in favor of throwing an HttpError instance. This allows all middlewares to optionally participate in error handling. Other properties have been moved or renamed to make it easier to re-use existing objects internally as a minor performance optimization.

Fresh 1.x Fresh 2.x
ctx.renderNotFound() throw new HttpError(404)
ctx.basePath ctx.config.basePath
ctx.remoteAddr ctx.info.remoteAddr

Getting help

If you run into problems with upgrading your app, reach out to us by creating an issue here https://github.com/denoland/fresh/issues/new . That way we can improve this migration guide for everyone.