onMount function in svelte doesn't work

[hoachnt]

code:

<script>
  import { onMount } from "svelte";

  onMount(() => {
    console.log("Not nice");
  });
</script>
<h1>New Weather</h1>
<form method="post" action={`/`}>
  <!-- Add input fields here -->
  <input type="submit" value="Create Weather" />
</form>
<br />

<a href={/}>Back</a>

error:

bud version: bud: 0.2.8 svelte: 3.47.0 react: 18.0.0