docs: Create guidelines for integrating Convex with Svelte/SvelteKit.

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# Convex + Svelte Guidelines
## Overview
These guidelines describe how to write **Convex** backend code **and** consume it from a **Svelte** (SvelteKit) frontend. The syntax for Convex functions stays exactly the same, but the way you import and call them from the client differs from a React/Next.js project. Below you will find the adapted sections from the original Convex style guide with Sveltespecific notes.
---
## 1. Function Syntax (Backend)
> **No change** keep the new Convex function syntax.
```typescript
import {
query,
mutation,
action,
internalQuery,
internalMutation,
internalAction
} from './_generated/server';
import { v } from 'convex/values';
export const getUser = query({
args: { userId: v.id('users') },
returns: v.object({ name: v.string(), email: v.string() }),
handler: async (ctx, args) => {
const user = await ctx.db.get(args.userId);
if (!user) throw new Error('User not found');
return { name: user.name, email: user.email };
}
});
```
---
## 2. HTTP Endpoints (Backend)
> **No change** keep the same `convex/http.ts` file.
```typescript
import { httpRouter } from 'convex/server';
import { httpAction } from './_generated/server';
const http = httpRouter();
http.route({
path: '/api/echo',
method: 'POST',
handler: httpAction(async (ctx, req) => {
const body = await req.bytes();
return new Response(body, { status: 200 });
})
});
```
---
## 3. Validators (Backend)
> **No change** keep the same validators (`v.string()`, `v.id()`, etc.).
---
## 4. Function Registration (Backend)
> **No change** use `query`, `mutation`, `action` for public functions and `internal*` for private ones.
---
## 5. Function Calling from **Svelte**
### 5.1 Install the Convex client
```bash
npm i convex @convex-dev/convex-svelte
```
> The `@convex-dev/convex-svelte` package provides a thin wrapper that works with Svelte stores.
### 5.2 Initialise the client (e.g. in `src/lib/convex.ts`)
```typescript
import { createConvexClient } from '@convex-dev/convex-svelte';
export const convex = createConvexClient({
url: import.meta.env.VITE_CONVEX_URL // set in .env
});
```
### 5.3 Using queries in a component
```svelte
<script lang="ts">
import { convex } from '$lib/convex';
import { onMount } from 'svelte';
import { api } from '../convex/_generated/api';
let user: { name: string; email: string } | null = null;
let loading = true;
let error: string | null = null;
onMount(async () => {
try {
user = await convex.query(api.users.getUser, { userId: 'some-id' });
} catch (e) {
error = (e as Error).message;
} finally {
loading = false;
}
});
</script>
{#if loading}
<p>Loading…</p>
{:else if error}
<p class="error">{error}</p>
{:else if user}
<h2>{user.name}</h2>
<p>{user.email}</p>
{/if}
```
### 5.4 Using mutations in a component
```svelte
<script lang="ts">
import { convex } from '$lib/convex';
import { api } from '../convex/_generated/api';
let name = '';
let creating = false;
let error: string | null = null;
async function createUser() {
creating = true;
error = null;
try {
const userId = await convex.mutation(api.users.createUser, { name });
console.log('Created user', userId);
} catch (e) {
error = (e as Error).message;
} finally {
creating = false;
}
}
</script>
<input bind:value={name} placeholder="Name" />
<button on:click={createUser} disabled={creating}>Create</button>
{#if error}<p class="error">{error}</p>{/if}
```
### 5.5 Using **actions** (Nodeonly) from Svelte
Actions run in a Node environment, so they cannot be called directly from the browser. Use a **mutation** that internally calls the action, or expose a HTTP endpoint that triggers the action.
---
## 6. Scheduler / Cron (Backend)
> Same as original guide define `crons.ts` and export the default `crons` object.
---
## 7. File Storage (Backend)
> Same as original guide use `ctx.storage.getUrl()` and query `_storage` for metadata.
---
## 8. TypeScript Helpers (Backend)
> Keep using `Id<'table'>` from `./_generated/dataModel`.
---
## 9. SvelteSpecific Tips
| Topic | Recommendation |
| ------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- |
| **Storebased data** | If you need reactive data across many components, wrap `convex.query` in a Svelte store (`readable`, `writable`). |
| **Error handling** | Use `try / catch` around every client call; surface the error in the UI. |
| **SSR / SvelteKit** | Calls made in `load` functions run on the server; you can use `convex.query` there without worrying about the browser environment. |
| **Environment variables** | Prefix with `VITE_` for clientside access (`import.meta.env.VITE_CONVEX_URL`). |
| **Testing** | Use the Convex mock client (`createMockConvexClient`) provided by `@convex-dev/convex-svelte` for unit tests. |
---
## 10. Full Example (SvelteKit + Convex)
### 10.1 Backend (`convex/users.ts`)
```typescript
import { mutation, query } from './_generated/server';
import { v } from 'convex/values';
export const createUser = mutation({
args: { name: v.string() },
returns: v.id('users'),
handler: async (ctx, args) => {
return await ctx.db.insert('users', { name: args.name });
}
});
export const getUser = query({
args: { userId: v.id('users') },
returns: v.object({ name: v.string() }),
handler: async (ctx, args) => {
const user = await ctx.db.get(args.userId);
if (!user) throw new Error('Not found');
return { name: user.name };
}
});
```
### 10.2 Frontend (`src/routes/+page.svelte`)
```svelte
<script lang="ts">
import { convex } from '$lib/convex';
import { api } from '$lib/convex/_generated/api';
import { onMount } from 'svelte';
let name = '';
let createdId: string | null = null;
let loading = false;
let error: string | null = null;
async function create() {
loading = true;
error = null;
try {
createdId = await convex.mutation(api.users.createUser, { name });
} catch (e) {
error = (e as Error).message;
} finally {
loading = false;
}
}
</script>
<input bind:value={name} placeholder="Your name" />
<button on:click={create} disabled={loading}>Create user</button>
{#if createdId}<p>Created user id: {createdId}</p>{/if}
{#if error}<p class="error">{error}</p>{/if}
```
---
## 11. Checklist for New Files
- ✅ All Convex functions use the **new syntax** (`query({ … })`).
- ✅ Every public function has **argument** and **return** validators.
- ✅ Svelte components import the generated `api` object from `convex/_generated/api`.
- ✅ All client calls use the `convex` instance from `$lib/convex`.
- ✅ Environment variable `VITE_CONVEX_URL` is defined in `.env`.
- ✅ Errors are caught and displayed in the UI.
- ✅ Types are imported from `convex/_generated/dataModel` when needed.
---
## 12. References
- Convex Docs [Functions](https://docs.convex.dev/functions)
- Convex Svelte SDK [`@convex-dev/convex-svelte`](https://github.com/convex-dev/convex-svelte)
- SvelteKit Docs [Loading Data](https://kit.svelte.dev/docs/loading)
---
_Keep these guidelines alongside the existing `svelte-rules.md` so that contributors have a single source of truth for both frontend and backend conventions._