Firebase adapter for SvelteKit.
Utilise the Firebase Hosting CDN with dynamic content served by SvelteKit on Cloud Functions!
✔️ SSR on
Cloud Functions
✔️ Integrates with existing Cloud Functions!
✔️ Local production testing with
Firebase Emulator
✔️ Mitigate cold-starts with
minInstances
✔️
Multiple Hosting Sites
- Setup
- Configuration Overview
- Details
- How it works
- Firebase Emulator local Testing
- Deployment
- Caveats
- Non-Goals
- FAQ
- Contributing
The adapter reads firebase.json
to determine output dirs for Server scripts &
Static assets, without this file the adapter cannot know how your Firebase app
is configured. Hosting & Cloud Functions are required.
In your standard SvelteKit project:
npm install --save-dev svelte-adapter-firebase
- add adapter to
svelte.config.js
:
+import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
+ adapter: firebase(),
},
};
- Setup
firebase.json
withfirebase init
. npm run build
. Read and repeat, the output is meant as a guide. IE: after your first build, you need to manually add the produced Cloud Function inindex.js
SvelteKit is still in Beta and the Adapter API is in flux, this can result in the Adapter and SvelteKit becoming incompatible. Here is a compatibility table:
Adapter Version | SvelteKit Version |
---|---|
0.14.0 |
1.0.0-next.330 |
0.13.1 |
1.0.0-next.180 |
0.13.0 |
1.0.0-next.168 |
0.12.x |
1.0.0-next.165 |
0.11.x |
1.0.0-next.155 |
NA |
1.0.0-next.152-154 |
0.10.x |
1.0.0-next.132 |
0.9.1 |
1.0.0-next.122 |
0.9.0 |
1.0.0-next.120 |
0.8.x |
1.0.0-next.111 |
NA |
1.0.0-next.109-110 |
0.7.x |
1.0.0-next.107 |
0.6.x |
1.0.0-next.103 |
0.5.x |
1.0.0-next.54 |
0.4.x |
1.0.0-next.46 |
0.3.x |
1.0.0-next.27 |
Note: only the versions listed have been tested together, if others happen to work, it is just coincidence. This is beta software after all.
Adapter options:
esbuildBuildOptions
- function to return an
esbuild.BuildOptions
object - default: see
defaultOptions
object insrc/index.js
- function to return an
firebaseJsonPath
- path to your
firebase.json
file, relative from wheresvelte build
is called - default:
./firebase.json
- path to your
target
- required when
firebase.json:hosting
is an array (contains many site configurations) - default:
undefined
- required when
sourceRewriteMatch
- used to lookup the rewrite config to determine whether to output SSR code for Cloud Functions. See Firebase Rewrite configuration docs.
- default:
**
Adapter output:
- static assets (images, CSS, Client-side JavaScript) of your SvelteKit app
output to the directory defined by
firebase.json:hosting.public
- server assets (SSR JavaScript) output alongside your Cloud Functions defined
by
firebase.json:functions.source
Setup outlines the steps most commonly used with a single SvelteKit
app. Here we go into the details of each configuration and how it interacts with
the firebase.json
config.
The 3 step process is:
- select Hosting config from
firebase.json
. If more than one site present in config, matchsvelte.config.js:target
field with eitherfirebase.json:hosting[].site
or.target
fields. - output static assets to the directory in the
public
field - identify the rewrite rule for SSR to determine Cloud Function output. The
rewrite rule is determined by a lookup of the
rewrites.source
againstsourceRewriteMatch
Due to the relaxed rules of firebase.json
we can have many valid configs. At a
minimum, one or more Hosting sites is required with an associated Functions
config if a Cloud Function rewrite is used. These are the combintations:
single Hosting site with Cloud Function rewrite
{
"hosting": {
"public": "<someDir>",
"rewrites": [
{
"source": "**",
"function": "<functionName>"
}
]
},
"functions": {
"source": "<anotherDir>"
}
}
multiple Hosting site with Cloud Function rewrite
{
"hosting": [
{
"site": "blog",
"public": "<someDir>",
"rewrites": [
{
"source": "**",
"function": "<functionName>"
}
]
},
{
// another site config
}
],
"functions": {
"source": "<anotherDir>"
}
}
To correctly lookup the blog
site, target
will need to be set in
svelte.config.js
:
import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
adapter: firebase({ target: "blog" }),
},
};
Detailed examples of the adapter configuration options.
All options:
import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
adapter: firebase({
esbuildBuildOptions: (defaultOptions: BuildOptions) => Promise<BuildOptions> | BuildOptions,
firebaseJsonPath: "",
target: "svelte-func-single-site",
sourceRewriteMatch: "",
}),
},
};
esbuildBuildOptions
As an escape hatch, you may optionally specify a function which will receive the final esbuild options generated by this adapter and returns a modified esbuild configuration. The result of this function will be passed as-is to esbuild. The function can be async.
For example, you may wish to add plugins
, or configure the
format
to bundle to ESM (defaults to
CJS):
import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
adapter: firebase({
target: "svelte-func-single-site",
esbuildBuildOptions(defaultOptions) {
return {
...defaultOptions,
target: "esm"
plugins: [],
};
},
})
},
};
The default options for this version are as follows:
{
entryPoints: ['.svelte-kit/firebase/handler.js'],
outfile: `pathToOutputDir/index.js`,
bundle: true,
inject: ['pathTo/shims.js'],
platform: 'node',
target: `node${functionRuntimeVersion}`
}
where esbuild target
is computed from the Node.js runtime version defined for
your Cloud Functions.
firebaseJsonPath
If the firebase.json
file is not in the directory you run svelte build
, then
you can set a relative path in svelte.config.js
:
.gitignore
firebase.json
app/ <-- svelte build run in this dir
package.json
svelte.config.js
src/
anotherApp/
index.html
index.css
functions/
package.json
index.js
import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
adapter: firebase({
target: "svelte-func-single-site",
firebaseJsonPath: "../firebase.json",
}),
},
};
target
If firebase.json:hosting
is an array of sites, then each hosting config must
list a site
or target
field that matches the adatper's target
option. For
example:
// firebase.json
{
"hosting": [
{
"site": "blog",
// or
// "target": "blog",
"public": "<someDir>",
"rewrites": [
{
"source": "**",
"run": {
"serviceId": "<cloudRunServiceId>"
}
}
]
},
{
"site": "adminPanel",
// or
// "target": "adminPanel",
"public": "<anotherDir>"
}
]
}
import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
adapter: firebase({ target: "blog" }),
target: "#svelte",
},
};
The Firebase config & adapter config match (firebase.json:hosting[0].site
===
adapter target
), so therefore we know which Firebase Hosting site you want to
build the SvelteKit site for.
sourceRewriteMatch
If the rewrite source
pattern is not **
, then svelte.config.js
sourceRewriteMatch
will need to be set to match your desired rewrite rule. For
example:
// firebase.json
{
"hosting": {
"public": "<someDir>",
"rewrites": [
{
"source": "/blog/**",
"run": {
"serviceId": "<cloudRunServiceId>"
}
}
]
}
}
import firebase from "svelte-adapter-firebase";
/** @type {import('@sveltejs/kit').Config} */
export default {
kit: {
adapter: firebase({ sourceRewriteMatch: "/blog/**" }),
target: "#svelte",
},
};
Given
- the following
firebase.json
configuration - a standard SvelteKit app structure
- the default
svelte-adapter-firebase
config
// firebase.json
{
"hosting": {
"public": "myApp",
"rewrites": [
{
"source": "**",
"function": "ssrServer"
}
],
"predeploy": ["npm run build"]
},
"functions": {
"source": "functions"
}
}
the following Server & Static assets dirs are created:
firebase.json ("public": "myApp")
package.json
svelte.config.js
src/
app.html
routes/
index.svelte
functions/
package.json ("main": "index.js")
index.js
sveltekit/ <-- Server Assets dir (code to be imported to you Cloud Function)
myApp/ <-- Static Assets to go to Firebase Hosting CDN
firebase.json:functions.source
dir is used to findfunctions/package.json
whosemain
field is used to find the Cloud Function build dir. This is used as the server asset output dir.
TypeScript Cloud Functions
Because we use the above method to determine the output dir, the server assets are output to the correct place when using TypeScript.
firebase.json ("public": "myApp")
package.json
svelte.config.js
src/
app.html
routes/
index.svelte
functions/
package.json ("main": "lib/index.js")
index.ts
lib/
index.js
sveltekit/ <-- Server assets output to functions/lib
myApp/ <-- Static assets to go to Firebase Hosting CDN
Output with Multiple Sites
In a multi-site setup, the site
or target
field from hosting config in
firebase.json
is used as the server output dir:
firebase.json ("site": "myCoolSite","public": "myApp")
package.json
svelte.config.js
src/
app.html
routes/
index.svelte
functions/
package.json
index.js
myCoolSite/ <-- Server assets
myApp/ <-- Static assets to go to Firebase Hosting CDN
The final piece is to write the actual Cloud Function source code to reference
the output server assets. The code is printed during svelte build
and should
be placed in your index.js
or index.ts
manually.
This is a flexible solution that allows integrating with other Cloud Functions
in your project. You can edit the provided code as you see fit. The
import/require of the generated code will not change unless you change the
firebase.json:hosting.site
or package.json:main
fields, so you shouldn't
need to update this code after adding it.
Test your production build locally before pushing to git or deploying!
- build your app:
svelte-kit build
- install Function dependencies:
pnpm install --prefix functions
- start the emulator:
firebase emulators:start
firebase deploy
🎉
- Using
firebase.json:hosting[].site
is preferred tofirebase.json:hosting[].target
as Firebase Deploy Targets only supports Hosting, Storage & Databases and not Functions. This means you can use Deploy targetstarget
field to identify your site for the adapter to build, but you CANNOT use Deploy Targes when deploying as you need to deploy the Hosting & Functions at the same time for this solution to work as expected. - Firebase Hosting Preview Channels currently lacks first-party support for SSR applications. This adapter doesn't attempt to remedy this issue and doesn't produce a different SSR Function for preview channel deployments.
⚠️ Cloud Function rewrites only support us-central1, other regions will error. The official warning about this can be found in these docs.
Write Cloud Function code directly into
.js
file instead of printing in console.
Firebase Cloud Functions have a long history of people configuring their index
files completely differently, some even generating them from directories.
Accommodating these would be a headache. Instead, all we look for is a match
against this string, ${name} =
, where name
is your Cloud Functions name. We
may make this configurable to a specific file in future.
Additionally, this allows for users to customise their Firebase Cloud Function
API like runWith()
options for memory/CPU, min/max Instances and
VPC/Ingress/Egress configuration settings, without complex support for options
in the adapter. This keeps the Function config where it should, close to the
userland code.
Handle the deployment of the app to Firebase.
Firebase apps consist of many different services with the CLI providing optional deployments. We do not want to dictate full deployments with your frontend nor perform partial deployments if it does not fit your app. The only option then is to leave it to you 🎉
Why is the Cloud Function code output to the terminal for me to add manually instead of being written to
functions/index.js
?
See non-goals Write Cloud Function code directly into .js
file
instead of printing in console.
Firebase libs in SvelteKit
As recommended in the SvelteKit FAQ, please use Firebase JS SDK v9 as the older version of the SDK has issues and a larger bundle size.
Cold Starts
Since the purpose of using this adapter is to leverage the Firebase Hosting CDN, you should consider improving the user experience with targetted caching/TTLs.
If cold start are still an issue for your application, Cloud Functions has
support for minInstances
which will keep X
number of instances warm. From
the docs:
A minimum number of instances kept running incur billing costs at idle rates. Typically, to keep one idle function instance warm costs less than $6.00 a month. The Firebase CLI provides a cost estimate at deployment time for functions with reserved minimum instances. Refer to Cloud Functions Pricing to calculate costs.
To implement this, configure your
runWith
options like so:
const myRuntimeOptions = {
memory: "1GB",
+ minInstances: 1,
}
exports.myFunc = functions.runWith(myRuntimeOptions).https.onRequest(async (request, response) => {
...
});
Note: this is still single concurrency (if an instance does not exist to handle a request when it hits the backend a new Function instance is created). Watch this space!
1.0.0
will not be published until the SvelteKit Adapter API is declared stable and SvelteKit is released for general use.
Contributions of any kind welcome, just follow the guidelines!
Short version:
git clone https://github.com/jthegedus/svelte-adapter-firebase.git
asdf install
pnpm i
See asdf to install set it up.
While building this adapter some issues were found with upstream components, these are captured here should someone wish to contribute them:
- Cloud Function validation code linked in
utils.js
is from two different sources which indicates that it is being validated byfirebase-tools
in two separate places. PR a fix there.