> For the complete documentation index, see [llms.txt](https://docs.millimetric.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.millimetric.ai/sdks/frameworks/svelte.md).

# Svelte / SvelteKit

Svelte 5 / SvelteKit + @millimetric/track.

## Install

```bash
npm i @millimetric/track
```

## SvelteKit — root layout

```svelte
<!-- src/routes/+layout.svelte -->
<script lang="ts">
  import { onMount } from "svelte";
  import { init } from "@millimetric/track";
  import { PUBLIC_AOA_KEY, PUBLIC_AOA_HOST } from "$env/static/public";

  let { children } = $props();

  onMount(() => {
    init({
      key: PUBLIC_AOA_KEY,
      host: PUBLIC_AOA_HOST ?? "https://api.millimetric.ai"
    });
  });
</script>

{@render children()}
```

The SDK patches `history.pushState`, so SvelteKit's client-side navigations auto-fire `$pageview`.

```bash
# .env
PUBLIC_AOA_KEY=pk_live_...
PUBLIC_AOA_HOST=https://api.millimetric.ai
```

## Identify on login

```svelte
<!-- src/lib/IdentifyOnAuth.svelte -->
<script lang="ts">
  import { identify } from "@millimetric/track";
  import { user } from "$lib/stores/auth";   // your auth store
  import { afterUpdate } from "svelte";

  $effect(() => {
    if ($user) identify($user.id, { email: $user.email, plan: $user.plan });
  });
</script>
```

Mount once in `+layout.svelte` next to your other auth-aware components.

(For Svelte 4, replace the `$effect` rune with a reactive statement: `$: if ($user) identify($user.id);`)

## Track on intent

```svelte
<script lang="ts">
  import { track } from "@millimetric/track";

  function onClickPricing(plan: "free" | "pro") {
    track("clicked_pricing", { plan });
  }
</script>

<button onclick={() => onClickPricing('pro')}>Choose Pro</button>
```

## Server-side events — `+server.ts`

Use `@millimetric/track-node` with an `sk_*` key. The variable goes in the **private** env namespace so it never ships to the client.

```ts
// src/lib/server/mm.ts
import { init, track, flush } from "@millimetric/track-node";
import { AOA_SK, AOA_HOST } from "$env/static/private";

init({ key: AOA_SK, host: AOA_HOST, flushAt: 1 });

export { track, flush };
```

```ts
// src/routes/api/signup/+server.ts
import { json } from "@sveltejs/kit";
import { track, flush } from "$lib/server/mm";

export async function POST({ request }) {
  const { anonymous_id, user_id, plan } = await request.json();

  track({
    event: "signup",
    anonymous_id,
    user_id,
    properties: { plan }
  });

  await flush();
  return json({ ok: true });
}
```

## Form actions

Same idea — call `track()` inside the `default` action, `flush()` before returning:

```ts
// src/routes/signup/+page.server.ts
import { fail } from "@sveltejs/kit";
import { track, flush } from "$lib/server/mm";

export const actions = {
  default: async ({ request, cookies }) => {
    const data = await request.formData();
    const email = String(data.get("email"));
    const aid = cookies.get("aid");

    // ... your signup logic ...

    track({
      event: "signup",
      anonymous_id: aid,
      user_id: createdUser.id,
      properties: { plan: "free" }
    });
    await flush();

    return { ok: true };
  }
};
```

## SSR safety

Don't import `@millimetric/track` in code that runs server-side — it touches `localStorage` and `navigator`. SvelteKit's `+page.server.ts` and `+layout.server.ts` files run on the server only; reach for `@millimetric/track-node` there instead.

`onMount` and `$effect` only fire on the client, so calling browser-SDK functions inside them is always safe.

## Plain Svelte (no SvelteKit)

Same flow, simpler init:

```svelte
<!-- App.svelte -->
<script lang="ts">
  import { onMount } from "svelte";
  import { init, track } from "@millimetric/track";

  onMount(() => init({ key: import.meta.env.VITE_AOA_KEY }));
</script>
```


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