Common Patterns

Fetch Data from Firestore for Authenticated Users

First, Use the SignedIn component to access the UID of the current user. Second, pass that UID to the Doc or Collection component to fetch a Firestore document owned by that user.

  <SignedIn let:user>
    <Doc ref={`posts/${user.uid}`} let:data={post}>

SSR with SvelteKit

SvelteFire is a client-side library, but allows you to hydrate server data into a realtime stream.

First, fetch data from a load function like so:

// +page.ts
import { doc, getDoc } from 'firebase/firestore';

export const load = (async () => {
  const ref = doc(firestore, 'posts', 'first-post');
  const snapshot = await getDoc(ref);
  return {

Second, pass the server data as the startWith value to a store. This will bypass the loading state and ensure the data is rendered in the server HTML, then realtime listeners will be attached afterwards.

// +page.svelte  
<script lang="ts">
  export let data: PageData;

<!-- Example using component -->
<Doc startWith={} ref="posts/first-post" let:data={post}>

Note: This will result in 2 reads from Firestore on initial page load, so only use this pattern when true realtime data necessary.

Dynamic Firestore Queries

Imagine you have a collection of posts what a user can filter by category. Create a reactive declaration to re-run the query whenever the category changes.

<script lang="ts">
    import { query, collection, where } from 'firebase/firestore';

    let category = 'tech';

    $: q = query(
            collection(firestore, `posts`),
            where('category', '==', category)

<Collection ref={q} let:data={posts}>
        {#each posts as post (}

<button on:click={() => category = 'sports'}>Sports</button>

Handle File Uploads with Progress Bar

The example below shows how to upload a file to Firebase Storage and display a progress bar. First, get a file from the user. Second, pass the file to the UploadTask component. Third, display the progress bar and download link.

<script lang="ts">
  let file: File;
  let filePath = "things/test.png";

  function chooseFile(event) {
    file =[0];

<input type="file" on:change={chooseFile} />

{#if file}
  <UploadTask ref={filePath} data={file} let:progress let:snapshot>
    {#if snapshot?.state === "running" || snapshot?.state === "success"}
      <p>{progress}% uploaded</p>
      <progress value={progress} max="100" />

    {#if snapshot?.state === "error"}
      Upload failed

    {#if snapshot?.state === "success"}
      <DownloadURL ref={snapshot?.ref} let:link let:ref>
        <a href={link} download> {ref?.name} </a>