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From SvelteKit to Nexy

In Nexy a SvelteKit project keeps its Svelte pages and layouts as plain .svelte files, while +server.ts, +page.server.ts loads, form actions and hooks move to Python files next to them.

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

Pick the mode first

Your SvelteKit app is Nexy mode Pages are
an app with client navigation client mode, useCSR = True .svelte files under src/routes/
mostly content, a few interactive parts server mode, the default .nexy pages with Svelte islands
nexyconfig.py
from nexy.core.models import NexyConfigModelfrom nexy.frontend import svelte  class NexyConfig(NexyConfigModel):    useFF = svelte()    useCSR = True    useAliases = {"@": "src"}

The sections below use client mode unless they say otherwise.

+page.svelte

src/routes/about/+page.svelte
<h1>About</h1>

A page is the file itself, named after its URL:

src/routes/about.svelte
<h1>About</h1>

src/routes/+page.svelte is src/routes/index.svelte.

Dynamic routes and params

src/routes/blog/[slug]/+page.svelte
<script lang="ts">  import { page } from "$app/state";</script> <h1>{page.params.slug}</h1>

The segments reach the page as props:

src/routes/blog/[slug].svelte
<script lang="ts">  let { slug }: { slug: string } = $props();</script> <h1>{slug}</h1>

In any other component, the params store of @nexy/client holds them: $params.slug. [...rest] and (group) folders work as in SvelteKit.

+layout.svelte

src/routes/+layout.svelte
<script lang="ts">  let { children } = $props();</script> <header>My app</header><main>{@render children()}</main>

There is no app.html: the root layout.svelte owns the document.

src/routes/layout.svelte
<script lang="ts">  import type { Snippet } from "svelte";  let { children }: { children?: Snippet } = $props();</script> <html>  <body>    <header>My app</header>    <main>{@render children?.()}</main>  </body></html>

+server.ts

src/routes/api/items/[id]/+server.ts
import { json } from "@sveltejs/kit"; export function GET({ params }) {  return json({ id: Number(params.id) });}

The same GET export, in Python:

src/routes/api/items/[id].py
async def GET(id: int):    return {"id": id}
src/routes/api/items/index.py
from pydantic import BaseModel, Field from nexy.http import JSONResponse  class NewItem(BaseModel):    name: str    price: float = Field(gt=0)  async def POST(item: NewItem):    return JSONResponse(item.model_dump(), status_code=201)

error()

src/routes/api/orders/[id]/+server.ts
import { error, json } from "@sveltejs/kit"; export function GET({ params, url }) {  if (Number(params.id) > 100) error(404, "No such order");  return json({ id: Number(params.id), currency: url.searchParams.get("currency") ?? "EUR" });}
src/routes/api/orders/[id].py
from nexy.http import HTTPException  async def GET(id: int, currency: str = "EUR"):    if id > 100:        raise HTTPException(status_code=404, detail="No such order")    return {"id": id, "currency": currency}

load in +page.server.ts

src/routes/users/+page.server.ts
export async function load() {  return { users: await db.user.findMany() };}
src/routes/users/+page.svelte
<script lang="ts">  let { data } = $props();</script> <ul>  {#each data.users as user (user.id)}    <li>{user.name}</li>  {/each}</ul>

In client mode the page asks a handler for its data:

src/routes/api/users.py
async def GET():    return [{"id": 1, "name": "Ada"}, {"id": 2, "name": "Alan"}]
src/routes/users.svelte
<script lang="ts">  let users = $state<{ id: number; name: string }[]>([]);   $effect(() => {    fetch("/api/users").then((response) => response.json()).then((list) => (users = list));  });</script> <ul>  {#each users as user (user.id)}    <li>{user.name}</li>  {/each}</ul>

In server mode the frontmatter of a .nexy page is the load function, and it runs while the server renders:

src/routes/people.nexy
---users = [{"id": 1, "name": "Ada"}, {"id": 2, "name": "Alan"}]---<ul>  {% for user in users %}  <li>{{ user.name }}</li>  {% endfor %}</ul>

Form actions and use:enhance

src/routes/todos/+page.server.ts
export const actions = {  default: async ({ request }) => {    const data = await request.formData();    await db.todo.create({ title: data.get("title") });  },};
src/routes/todos/+page.svelte
<script lang="ts">  import { enhance } from "$app/forms";</script> <form method="POST" use:enhance>  <input name="title" />  <button>Add</button></form>

An action is a Python function with a generated, typed client:

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.svelte
<script lang="ts">  import { useAction } from "@nexy/client";  import { add_todo } from "@nexy/actions";   let title = $state("");  const save = useAction(add_todo, { onSuccess: () => (title = "") });</script> <form onsubmit={(e) => { e.preventDefault(); save.run({ title }); }}>  <input bind:value={title} />  <button disabled={$save.pending}>Add</button></form>

revalidate("/todos") plays the part of invalidateAll(): the page fetches itself again.

src/lib/Nav.svelte
<script lang="ts">  import { goto } from "$app/navigation";  import { page } from "$app/state";</script> <a href="/about">About</a><span>{page.url.pathname}</span><button onclick={() => goto("/dashboard")}>Dashboard</button>
src/components/Nav.svelte
<script lang="ts">  import Link from "@nexy/Link.svelte";  import { pathname, router } from "@nexy/client";</script> <Link href="/about" activeClass="active">About</Link><span>{$pathname}</span><button onclick={() => router.push("/dashboard")}>Dashboard</button>

hooks.server.ts

src/hooks.server.ts
export async function handle({ event, resolve }) {  if (event.url.pathname.startsWith("/dashboard") && !event.cookies.get("session")) {    return new Response(null, { status: 307, headers: { location: "/login" } });  }  const response = await resolve(event);  response.headers.set("x-app", "demo");  return response;}

The path test is the folder. A root middleware.py wraps everything, a dashboard/middleware.py only the routes below it:

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
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}

prerender and entries

src/routes/blog/[slug]/+page.ts
export const prerender = true; export function entries() {  return [{ slug: "hello" }, { slug: "world" }];}

Export getStaticParams from the page for one pre-rendered document per value:

src/routes/posts/[slug].svelte
<script lang="ts" module>  export function getStaticParams() {    return [{ slug: "hello" }, { slug: "world" }];  }</script> <script lang="ts">  let { slug }: { slug: string } = $props();</script> <h1>{slug}</h1>

In server mode, revalidate = 60 in the frontmatter of a .nexy page caches it per URL instead:

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

<svelte:head>

src/routes/blog/+page.svelte
<svelte:head>  <title>Blog</title></svelte:head>

In client mode, write the tags in the root layout.svelte. In server mode a .nexy page sets them, and its layout writes them with {{ useMetadata().html() }}:

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

Svelte components in server pages

src/components/Counter.svelte
<script lang="ts">  let { start = 0 }: { start?: number } = $props();  let count = $state(start);</script> <button onclick={() => count++}>{count}</button>

In server mode the component is an island of a .nexy page:

src/routes/home.nexy
---from "@/components/Counter.svelte" import Counter---<h1>Static heading</h1><Counter start=3 directive="client:visible" />

+error.svelte

src/routes/notfound.svelte answers unknown URLs in client mode, notfound.nexy in server mode, and API clients get {"detail": ...}.

$env/static/private

src/lib/server/db.ts
import { DATABASE_URL } from "$env/static/private";
src/settings.py
import os DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///dev.db")

Running

SvelteKit Nexy
npx sv create nx new, template web-fbr-svelte
vite dev nx dev
vite build with an adapter, then node build nx build, then nx start
static/ public/, served at /
src/lib/ and $lib src/components/ and @

Next steps

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