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From Next.js to Nexy

In Nexy a Next.js App Router project keeps its file routes, layouts and React components, while server code, route handlers and Server Actions move to Python files next to them.

Each section below shows a Next.js habit, then the same thing in Nexy.

Pick the mode first

A Next.js app mixes server and client components in one tree. A Nexy project picks one of two shapes in nexyconfig.py:

Your Next.js app is Nexy mode Pages are
mostly interactive, client navigation client mode, useCSR = True .tsx files, as in app/
mostly content, a few interactive parts server mode, the default .nexy pages with React islands
nexyconfig.py
from nexy.core.models import NexyConfigModelfrom nexy.frontend import react  class NexyConfig(NexyConfigModel):    useFF = react()    useCSR = True

The sections below use client mode unless they say otherwise. See Server mode and client mode.

page.tsx

app/about/page.tsx
export default function About() {  return <h1>About</h1>;}

A page is the file itself, not a page.tsx inside a folder:

src/routes/about.tsx
export default function About() {  return <h1>About</h1>;}

app/page.tsx is src/routes/index.tsx, and app/blog/page.tsx is src/routes/blog/index.tsx.

Route files, App Router and Pages Router

Both routers of Next.js map to src/routes/. A file of the Pages Router keeps its path; a page.tsx of the App Router becomes index.tsx, or a file named after its folder:

Next.js Nexy
pages/about.tsx src/routes/about.tsx
pages/blog/[slug].tsx src/routes/blog/[slug].tsx
app/about/page.tsx src/routes/about/index.tsx, or src/routes/about.tsx
app/blog/[slug]/page.tsx src/routes/blog/[slug]/index.tsx, or src/routes/blog/[slug].tsx
app/docs/[...slug]/page.tsx src/routes/docs/[...slug].tsx
app/(marketing)/pricing/page.tsx src/routes/(marketing)/pricing.tsx
pages/api/items/[id].ts src/routes/api/items/[id].py
app/api/items/[id]/route.ts src/routes/api/items/[id].py, or src/routes/api/items/[id]/index.py

A .tsx file is a page and a .py file is a handler: the extension says which, so a route handler loses its /route folder.

Dynamic segments and params

app/blog/[slug]/page.tsx
export default async function Post({ params }: { params: Promise<{ slug: string }> }) {  const { slug } = await params;  return <h1>{slug}</h1>;}
src/routes/blog/[slug].tsx
import { useParams } from "@nexy/client"; export default function Post() {  const { slug } = useParams<{ slug: string }>();  return <h1>{slug}</h1>;}

[...slug] and route groups such as (marketing) work as in Next.js.

generateStaticParams

app/blog/[slug]/page.tsx
export async function generateStaticParams() {  return [{ slug: "hello" }, { slug: "world" }];}

The same export, under this name or getStaticParams, gives one pre-rendered document per value. Nexy calls it without await, so return the array itself:

src/routes/blog/[slug].tsx
import { useParams } from "@nexy/client"; export function getStaticParams() {  return [{ slug: "hello" }, { slug: "world" }];} export default function Post() {  const { slug } = useParams<{ slug: string }>();  return <h1>{slug}</h1>;}

layout.tsx

app/layout.tsx
export default function RootLayout({ children }: { children: React.ReactNode }) {  return (    <html lang="en">      <body>{children}</body>    </html>  );}

The same file, one folder up: the root layout owns <html>, and a layout.tsx in a subfolder nests inside it.

src/routes/layout.tsx
import type { ReactNode } from "react"; export default function RootLayout({ children }: { children: ReactNode }) {  return (    <html lang="en">      <head>        <title>My app</title>      </head>      <body>{children}</body>    </html>  );}

metadata

app/blog/page.tsx
export const metadata = { title: "Blog", description: "Posts about Nexy" };

A .tsx page has no metadata export: write the tags in the root layout. In server mode, a .nexy page sets them per page:

src/routes/blog.nexy
---metadata = {"title": "Blog", "description": "Posts about Nexy"}---<h1>Blog</h1>

The root layout.nexy writes the tags where Next.js would, in the <head>:

src/routes/layout.nexy
---from nexy import useMetadata children: prop[NexyElement]---<!DOCTYPE html><html>  <head>{{ useMetadata().html() }}</head>  <body>{{ children | safe }}</body></html>
app/nav.tsx
"use client";import Link from "next/link";import { usePathname, useRouter } from "next/navigation";

The same names, from @nexy/client:

src/components/Nav.tsx
import { Link, usePathname, useRouter } from "@nexy/client"; export function Nav() {  const pathname = usePathname();  const router = useRouter();  return (    <nav>      <Link href="/">Home</Link>      <Link href="/about" activeClassName="active">About</Link>      <span>{pathname}</span>      <button onClick={() => router.push("/dashboard")}>Dashboard</button>    </nav>  );}

Route handlers

app/api/items/[id]/route.ts
export async function GET(request: Request, { params }: { params: Promise<{ id: string }> }) {  const { id } = await params;  return Response.json({ id: Number(id) });}

The same GET export, in Python, without /route:

src/routes/api/items/[id].py
async def GET(id: int):    return {"id": id}

A body is a Pydantic model, and /docs lists every handler:

src/routes/api/items/index.py
from pydantic import BaseModel from nexy.http import JSONResponse  class NewItem(BaseModel):    name: str  async def POST(item: NewItem):    return JSONResponse({"created": item.name}, status_code=201)

Server Actions and revalidatePath

app/actions.ts
"use server";import { revalidatePath } from "next/cache"; export async function addTodo(title: string) {  await db.todo.create({ data: { title } });  revalidatePath("/todos");}

An action is a Python function. Nexy generates its typed client in @nexy/actions:

src/actions/todos.py
from pydantic import BaseModel from nexy.decorators import Action, revalidate  class Todo(BaseModel):    title: str    done: bool = False  @Actionasync def add_todo(title: str) -> Todo:    revalidate("/todos")    return Todo(title=title)
src/routes/todos.tsx
import { useAction } from "@nexy/client";import { add_todo } from "@nexy/actions"; export default function Todos() {  const { run, pending, error, data } = useAction(add_todo);  return (    <button disabled={pending} onClick={() => run({ title: "Write the docs" })}>      {error ? error.message : data ? `Added ${data.title}` : "Add"}    </button>  );}

useActionState and useFormStatus map to the pending, error and data of useAction.

Server components are .nexy pages

app/users/page.tsx
export default async function Users() {  const users = await db.user.findMany();  return <ul>{users.map((user) => <li key={user.id}>{user.name}</li>)}</ul>;}

A Next.js server component runs on the server, reads data and sends HTML. A .nexy page is the same thing in server mode: its frontmatter is the body of the async component, in Python, and the template is what it returns.

src/routes/people.nexy
---users = [{"id": 1, "name": "Ada"}, {"id": 2, "name": "Alan"}]---<ul>  {% for user in users %}  <li>{{ user.name }}</li>  {% endfor %}</ul>
Next.js server component .nexy page
app/users/page.tsx, no "use client" src/routes/users.nexy
await db.user.findMany() in the component a query in the frontmatter
{params} and {searchParams} slug: prop[str] and useSearchParams()
cookies() and headers() from next/headers useCookies() and useHeaders()
export const revalidate = 60 revalidate = 60
a "use client" component inside it an island: <Counter directive="client:load" />

In client mode, a .tsx page runs in the browser, so it reads the data from a handler:

src/routes/api/users.py
async def GET():    return [{"id": 1, "name": "Ada"}, {"id": 2, "name": "Alan"}]
src/routes/users.tsx
import { useEffect, useState } from "react"; type User = { id: number; name: string }; export default function Users() {  const [users, setUsers] = useState<User[]>([]);  useEffect(() => {    fetch("/api/users").then((response) => response.json()).then(setUsers);  }, []);  return <ul>{users.map((user) => <li key={user.id}>{user.name}</li>)}</ul>;}

"use client" components inside server pages

app/page.tsx
import Counter from "./counter"; // "use client" export default function Home() {  return (    <>      <h1>Static heading</h1>      <Counter />    </>  );}

In server mode, the client component is an island, and its directive says when it hydrates:

src/routes/home.nexy
---from "@/components/Counter.tsx" import Counter---<h1>Static heading</h1><Counter start=3 directive="client:visible" />
src/components/Counter.tsx
import { useState } from "react"; export default function Counter({ start = 0 }: { start?: number }) {  const [count, setCount] = useState(start);  return <button onClick={() => setCount(count + 1)}>{count}</button>;}

See Islands for client:load, client:idle, client:visible and client:media.

ISR with revalidate

app/news/page.tsx
export const revalidate = 60;

The same line, in the frontmatter of a server-mode page:

src/routes/news.nexy
---revalidate = 60---<h1>News</h1>

middleware.ts

middleware.ts
import { NextResponse, type NextRequest } from "next/server"; export function middleware(request: NextRequest) {  if (!request.cookies.get("session")) return NextResponse.redirect(new URL("/login", request.url));} export const config = { matcher: "/dashboard/:path*" };

The matcher is the folder: a middleware.py in dashboard/ wraps every route below it.

src/routes/dashboard/middleware.py
from nexy.http import RedirectResponse, Request  async def middleware(request: Request, call_next):    if "session" not in request.cookies:        return RedirectResponse("/login", status_code=307)    return await call_next(request)
src/routes/dashboard/stats.py
async def GET():    return {"visits": 12}

notFound() and not-found.tsx

app/blog/[slug]/page.tsx
import { notFound } from "next/navigation"; if (!post) notFound();

In a handler, raise; in a server-mode page, call notFound():

src/routes/api/posts/[slug].py
from nexy.http import HTTPException POSTS = {"hello": "Hello, world"}  async def GET(slug: str):    if slug not in POSTS:        raise HTTPException(status_code=404, detail="No such post")    return {"title": POSTS[slug]}

app/not-found.tsx is src/routes/notfound.tsx in client mode, and notfound.nexy in server mode.

next/image

import Image from "next/image"; <Image src="/logo.png" alt="Logo" width={128} height={32} />

In a .nexy page, the Image component of nexy:

src/routes/brand.nexy
---from nexy import Image---<Image src="/logo.png" alt="Logo" width=128 height=32 />

Running

Next.js Nexy
npx create-next-app nx new, template web-fbr-react
next dev nx dev
next build && next start nx build, then nx start
public/ public/, served at /
Node at runtime Python at runtime; Node only builds the client bundles

Next steps

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