SvelteFire

A minimal, yet powerful library that puts realtime Firebase data into Svelte stores.

Experimental! Do not use in production.

<!-- 1. 🔥 Firebase App -->
<FirebaseApp {auth} {firestore}>

    <!-- 2. 👤 Get the current user -->
    <User let:user>

        <p>Howdy, {user.uid}</p>

        <!-- 3. 📜 Get a Firestore document owned by a user -->
        <Doc ref={`posts/${user.uid}`} let:data={post} let:ref={postRef}>
            
            <h2>{post.title}</h2>

            <!-- 4. 💬 Get all the comments in its subcollection -->
            <Collection ref={postRef.path + '/comments'} let:data={comments}>
                {#each comments as comment}

                {/each}
...

Why?

Svelte makes it possible to dramatically simplify the way developers work with Firebase. Here are some problems the project solves:

• Access users and realtime Firestore data as Svelte stores
• Automatic subscription disposal to prevent memory/cost leaks
• Better TypeScript experience for Firebase
• Handle complex relational data between Auth and Firestore
• Easily hydrate SvelteKit server data into a realtime Firebase stream

Quick Start

1. Install Firebase npm i firebase v9+ and initialize it in a file like lib/firebase.js:

npm i sveltefire firebase

import { initializeApp } from 'firebase/app';
import { getFirestore } from 'firebase/firestore';
import { getAuth } from 'firebase/auth';

// Initialize Firebase
const app = initializeApp(/* your firebase config */);
export const db = getFirestore(app);
export const auth = getAuth(app);

2. Get the Current user

<script>
  import { auth } from '$lib/firebase';
  import { userStore } from 'sveltefire';
  const user = userStore(auth);
</script>

Hello {$user?.uid}

3. Listen to realtime data.

Use the $ as much as you want - it will only result in one Firebase read request. When the all subscriptions are removed, it will automatically unsubscribe.

<script>
  import { firestore } from '$lib/firebase';
  import { docStore } from 'sveltefire';

  const post = docStore(firestore, 'posts/test');
</script>

{$post?.content}
{$post?.title}

Or better yet, use the built in Doc and Collection components. See below.

Stores

Stores are the building blocks of SvelteFire.

Auth Store

Listen to the current user. Render UI conditionally based on the auth state:

<script>
  import { userStore } from 'sveltefire';

  const user = userStore(auth);
</script>

{#if $user}
    <p>Hi {$user.uid}</p>
{:else}
    <p>Sign in...</p>
{/if}

Firestore Stores

Subscribe to realtime data. The store will unsubscribe automatically to avoid unnecessary Firestore reads.

<script>
  import { docStore, collectionStore } from 'sveltefire';

  const post = docStore(firestore, 'posts/test');

  // OR 

  const posts = collectionStore(firestore, 'posts');
</script>

{$post?.content}

{#each $posts as p}

{/each}

Cast Firebase data to a TS interface:

interface Post {
    id: string;
    title: string;
    content: string;
}
const post = docStore<Post>(firestore, 'posts/test');
const posts = collectionStore<Post>(firestore, 'posts'); // returns 

Hydrate server-fetched data from SvelteKit into a realtime feed:

// Data fetched via server
export let data: PageData;

// Just give the store a startWith value 
const store = docStore(db, 'posts/test', data.thing);

Update doc from svelte store capabilities

const post = docStore(db, 'posts/test');
$post = data.thing;

<button on:click={()=>{$post.likes++}}> 
  {$post.likes} Likes 
</button>

Realtime Components

In addition to stores, SvelteFire provides a set of components that can build complex realtime apps without leaving the HTML.

FirebaseApp

Technically optional, this component puts Firebase into Svelte context. This avoids the need to pass auth and firestore down to every component. All other components should be nested below it.

<script>
  // Initialize Firebase...
  const db = getFirestore(app);
  const auth = getAuth(app);
</script>

<FirebaseApp {auth} {firestore}>

    <User let:user></User>
    <!-- other sveltefire components here -->

</FirebaseApp>

Note: Components outside a FirebaseApp will need the auth/firestore prop, i.e <User auth={auth}>

User

Get the current user.

<User let:user>
    Hello {user.uid}

    <div slot="signedOut">You are signed out</div>
</User>

Doc

Fetch a single document and listen to data in realtime. The data slot prop provides access to the fetched data, while ref is the Firestore document reference.

<Doc ref="posts/test" let:data let:ref>
    {data.content}
    {ref.path}
</Doc>

Slot props can be renamed:

<Doc ref="posts/test" let:data={post} let:ref={postRef}>
    {post.content}
    {postRef.path}
</Doc>

All Firestore components can also handle loading states:

<Doc path="posts/test">
    <!-- data renders here in the default slot -->
    <div slot="loading">Loading.... This will disappear when data is defined</div>
</Doc>

Pass a startWith value to bypass the loading state. This is useful in SvelteKit when you need to hydrate server data into a realtime stream:

<Doc ref="posts/test" startWith={dataFromServer} />

Collection

Collections provides array of objects containing the document data, as well as the id and ref for each result. It also provides a count slot prop for number of docs in the query.

<Collection ref="posts" let:data let:count>
  <p>Fetched {count} documents</p>
  {#each data as post}
    {post.id}
    {post.ref.path}
    {post.content}
  {/each}
</Collection>

Collections can also take a Firestore Query instead of a path:

<script>
    const testQuery = query(collection(firestore, 'posts'), where('test', '==', 'test'));
</script>

<Collection ref={testQuery} let:data>
</Collection>

For complex queries that required dynamic data, it can be useful to build the query reactively.

<script>
  $: buildQuery = (uid:string) => {
    return query(collection(firestore, 'posts'), where('uid', '==', uid));
  }
</script>

<User let:user>
  <Collection ref={buildQuery(user.uid)} />
</User>

Using Components Together

These components can be combined to build complex realtime apps. It's especially powerful when fetching data that requires the current user's UID or a related document's path.

<FirebaseApp {auth} {firestore}>
  <User let:user>
      <p>UID: {user.uid}</p>
      

      <h3>Profile</h3>
      <Doc ref={`posts/${user.uid}`} let:data={profile} let:ref={profileRef}>

        {profile.content}


        <h4>Comments</h4>
        <Collection ref={profileRef.path + '/comments'} let:data={comments}>
          {#each comments as comment}
            <strong>{comment.content}</strong>
          {/each}

          <div slot="loading">Loading Comments...</div>
        </Collection>

        <div slot="loading">Loading Profile...</div>
      </Doc>

      <div slot="signedOut">Signed out</div>
  </User>
</FirebaseApp>

Notes

• This library should only run the the client, it is not for server-side data fetching.
• Requires Firebase v9 or greater.
• I've have not been able to get TS generics to work right in the components yet, so no intellisense on the data slot prop.
• How should we bundle it properly?