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From Astro to Nexy

A Nexy .nexy page is an Astro page with Python in its --- frontmatter instead of TypeScript: the same server-first HTML, the same islands and client:* directives, rendered on each request.

Each section below shows an Astro habit, then the same thing in Nexy.

A page

src/pages/about.astro
---const title = "About";---<h1>{title}</h1>

The frontmatter is Python and the template is Jinja2:

src/routes/about.nexy
---title = "About"---<h1>{{ title }}</h1>

src/pages/ is src/routes/, and index.astro is index.nexy.

Loops and conditions

src/pages/users.astro
---const users = [{ name: "Ada", admin: true }, { name: "Alan", admin: false }];---<ul>  {users.map((user) => <li>{user.name}{user.admin && <strong> admin</strong>}</li>)}</ul>
src/routes/users.nexy
---users = [{"name": "Ada", "admin": True}, {"name": "Alan", "admin": False}]---<ul>  {% for user in users %}  <li>{{ user.name }}{% if user.admin %}<strong> admin</strong>{% endif %}</li>  {% endfor %}</ul>

Components and Astro.props

src/components/Card.astro
---const { title, tone = "neutral" } = Astro.props;---<article class={`card card-${tone}`}>  <h2>{title}</h2>  <slot /></article>

Props are declared with prop[...], a default is a Python default, and <slot /> is <Slot />:

src/components/Card.nexy
---title: prop[str]tone: prop[str] = "neutral"---<article class="card card-{{ tone }}">  <h2>{{ title }}</h2>  <Slot /></article>
src/routes/index.nexy
---from "@/components/Card.nexy" import Card---<Card title="Latest" tone="warm">  <p>This week</p></Card>

@ is src/: nx new writes useAliases = {"@": "src"} in nexyconfig.py.

Layouts

src/layouts/Base.astro
---const { title } = Astro.props;---<html>  <head><title>{title}</title></head>  <body><slot /></body></html>
src/pages/about.astro
---import Base from "../layouts/Base.astro";---<Base title="About"><h1>About</h1></Base>

A page does not import its layout: the nearest layout.nexy above it wraps it, and the root one owns the document.

src/routes/layout.nexy
---from nexy import useMetadata children: prop[NexyElement]---<!DOCTYPE html><html>  <head>{{ useMetadata().html() }}</head>  <body>{{ children | safe }}</body></html>

The title and meta tags

The title prop of the layout becomes metadata in the page, which useMetadata().html() writes in the <head> of the layout above:

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

Dynamic routes and getStaticPaths

src/pages/posts/[slug].astro
---export function getStaticPaths() {  return [    { params: { slug: "hello" }, props: { title: "Hello" } },    { params: { slug: "world" }, props: { title: "World" } },  ];}const { title } = Astro.props;---<h1>{title}</h1>

A dynamic .nexy page renders on request, so there is no list of paths: the segment is a prop, and an unknown one is a 404.

src/routes/posts/[slug].nexy
---from nexy import notFound POSTS = {"hello": "Hello", "world": "World"} slug: prop[str]if slug not in POSTS:    notFound()title = POSTS[slug]---<h1>{{ title }}</h1>

[...path].astro is [...path].nexy.

Islands and client:*

src/pages/index.astro
---import Counter from "../components/Counter.tsx";---<h1>Static heading</h1><Counter start={3} client:visible />

The directive becomes a directive attribute, with the same values:

src/routes/home.nexy
---from "@/components/Counter.tsx" import Counter---<h1>Static heading</h1><Counter start=3 directive="client:visible" />
Astro Nexy
client:load directive="client:load", or no directive
client:idle directive="client:idle"
client:visible directive="client:visible"
client:media="(min-width: 768px)" directive="client:media" media="(min-width: 768px)"
client:only="react" accepted, but never hydrates: use client:load

The framework is set once in nexyconfig.py, and a project uses one:

nexyconfig.py
from nexy.core.models import NexyConfigModelfrom nexy.frontend import react  class NexyConfig(NexyConfigModel):    useFF = react()    useAliases = {"@": "src"}

Markdown pages

src/pages/changelog.md
---layout: ../layouts/Base.astro---# Changelog

A .md file under src/routes/ is a page, wrapped in the nearest layout with no layout: key:

src/routes/changelog.md
# Changelog Version 2.2 is out.

.mdx pages work too, with React or Preact as the framework. See Markdown and MDX.

API endpoints

src/pages/api/items/[id].ts
export function GET({ params }) {  return Response.json({ id: Number(params.id) });}
src/routes/api/items/[id].py
async def GET(id: int):    return {"id": id}

A body is a Pydantic model, validated before the function runs:

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)

Astro.redirect, Astro.cookies and Astro.url

src/pages/account.astro
---const theme = Astro.cookies.get("theme")?.value ?? "light";if (!Astro.cookies.has("session")) return Astro.redirect("/login");const page = Astro.url.searchParams.get("page") ?? "1";---<p>{theme} theme, page {page}</p>

The same reads are hooks, and the redirect is a function:

src/routes/account.nexy
---from nexy import redirect, useCookies, useSearchParams cookies = useCookies()if "session" not in cookies:    redirect("/login")theme = cookies.get("theme", "light")page = useSearchParams().get("page", "1")---<p>{{ theme }} theme, page {{ page }}</p>

Middleware

src/middleware.ts
export function onRequest(context, next) {  return next().then((response) => {    response.headers.set("x-app", "demo");    return response;  });}
src/routes/middleware.py
from nexy.http import Request  async def middleware(request: Request, call_next):    response = await call_next(request)    response.headers["x-app"] = "demo"    return response

A middleware.py in a subfolder only wraps the routes below it, which replaces the path checks inside onRequest.

Astro Actions

src/actions/index.ts
import { defineAction } from "astro:actions";import { z } from "astro:schema"; export const server = {  addNote: defineAction({    accept: "form",    input: z.object({ title: z.string() }),    handler: async ({ title }) => ({ title }),  }),};
src/pages/notes.astro
---import { actions } from "astro:actions";---<form method="POST" action={actions.addNote}>  <input name="title" />  <button>Add</button></form>

An action is a Python function in src/actions/; a form posts to its path:

src/actions/notes.py
from nexy.decorators import Action NOTES: list[str] = []  @Actionasync def add_note(title: str) -> None:    NOTES.append(title)
src/routes/notes.nexy
---from src.actions.notes import NOTES---<form method="post" action="{{ __actions_path['add_note'] }}">  <input name="title">  <button type="submit">Add</button></form><ul>  {% for note in NOTES %}  <li>{{ note }}</li>  {% endfor %}</ul>

From an island, useAction(add_note) in @nexy/client calls the same function with typed input.

<Image />

---import { Image } from "astro:assets";import logo from "../assets/logo.png";---<Image src={logo} alt="Logo" width={128} height={32} />
src/routes/brand.nexy
---from nexy import Image---<Image src="/logo.png" alt="Logo" width=128 height=32 />

404.astro

src/pages/404.astro
<h1>Not found</h1>
src/routes/notfound.nexy
<h1>Not found</h1>

API clients still get {"detail": "Not Found"}.

Static output and on-demand rendering

Astro builds static HTML by default and renders on demand with output: "server" or export const prerender = false. Nexy renders every page on request, and caches the ones you choose per URL:

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

There is no static export: nx start serves the site. See Rendering.

Running

Astro Nexy
npm create astro@latest nx new
astro dev nx dev
astro build and astro preview nx build, then nx start
public/ public/, served at /
astro add react nx new with a framework, or useFF = react()

Next steps

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