Using Netlify Functions with SvelteKit

Using Netlify Functions with SvelteKit

Using Netlify Functions with SvelteKit


☁️ Using Netlify Functions with SvelteKit

Why would you want to be using Netlify Functions with SvelteKit instead of the inbuilt SvelteKit functionality? Like NextJS from the React world SvelteKit supports server side rendering as well as server side routes from which you can run your server side code. There are a couple of reasons that come to mind for using Netlify functions with SvelteKit though. Firstly, if you are migrating your site from another platform and have existing Netlify functions, you can speed up the migration by transplanting over the existing Netlify functions.

Another reason for using Netlify functions in your SvelteKit app is to gain access to other languages in your functions. You can write Netlify functions in Rust among other languages. Using API server routes in SvelteKit, you would be limited to JavaScript. You might choose Rust over JavaScript when performance is critical as typically you can optimise Rust code to run faster than equivalent JavaScript.

The good news is (as we will see in a moment) that besides a couple of configuration files, you don't need much to get your Netlify functions working in tandem with SvelteKit.

🧑🏽‍🎓 How to Get Started Using Netlify Functions with SvelteKit

We'll look at these three steps in turn which will get you using Netlify Functions with SvelteKit in no time:

  1. netlify.toml configuration file,

  2. Netlify adapter,

  3. create functions.

⚙️ netlify.toml Config File

Create a netlify.toml file in the root directory of your project and add the following content:

command = "npm run build"
publish = "build"
command = "svelte-kit dev"
directory = "netlify/functions"
node_bundler = "esbuild"

Probably the most important part here is specifying the directory where we will put the Netlify functions (netlify/functions).

🔌 Netlify Adapter

Svelte has build adapters which help customise your site build for your hosting platform. This is exactly what the Netlify adapter does . Part of its work is to convert any server endpoints to Netlify functions. This means your build app will have a render function (generated by the adapter) as well as any Netlify functions you define yourself.

The SvelteKit adapters are still evolving. As such, current best practice is to choose the next version, which you can install with pnpm, npm or yarn:

pnpm i -D @sveltejs/[email protected]

On top, you will need to let SvelteKit know that you want it to use this adapter:

1/** @type {import('@sveltejs/kit').Config} */
2import adapter from '@sveltejs/adapter-netlify';
3import { imagetools } from 'vite-imagetools';
4import { mdsvex } from 'mdsvex';
5import preprocess from 'svelte-preprocess';
7const config = {
8 extensions: ['.svelte', '.md', ''],
9 preprocess: [
10 mdsvex({ extensions: ['', '.md', '.svx'] }),
11 preprocess({
12 scss: {
13 prependData: "@import 'src/lib/styles/variables.scss';",
14 },
15 }),
16 ],
17 kit: {
18 adapter: adapter(),
19 files: {
20 hooks: 'src/hooks',
21 },
22 // hydrate the <div id="svelte"> element in src/app.html
23 target: '#svelte',
24 vite: {
25 define: {
26 'process.env.VITE_BUILD_TIME': JSON.stringify(new Date().toISOString()),
27 },
28 plugins: [imagetools({ force: true })],
29 },
30 },
33export default config;

Import the adapter to your svelte.config.js file (line 2) and then set it as SvelteKit's adapter (line 18).

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🖥 The Netlify Functions

Next you can create the netlify/functions directory in your project and add any functions there. You are not limited to JavaScript here. Take a look at the post on using Rust for Netlify functions to get started with other languages.

Here are a couple of JavaScript test functions you can use to try out your setup. The first can be used to get a client IP. You might need this if you are doing spam detection. The second just returns a JSON object:

exports.handler = async (event, _, callback) => {
const ip = event.headers['x-forwarded-for'];
const client = ip.split(',')[0];
callback(null, {
statusCode: 200,
body: client,
exports.handler = async function () {
return {
statusCode: 200,
body: JSON.stringify({ message: 'Good morning!' }),

💯 Testing it out

Using Netlify Functions with SvelteKit: test output for good morning function show stringifed J S O N object in browser. Object has a message field whose value is Good morning!
Screenshot: Using Netlify Functions with SvelteKit: Test Function

In the Netlify tradition, configuration and boilerplate are kept to a minimum. To get these functions running, you should just need to commit these changes to your git repository, and deploy as normal. To test the client-ip function, you need to point your browser to the /.netlify/functions/client-ip route (see the working example here: ). Similarly for the good-morning function, point your browser to /.netlify/functions/good-morning. Again, there is a live test site at .

I have also created a full working repo on the Rodney Lab GitHub page .

🙌🏽 Wrapup

In this post we saw:

  • why you might want to use Netlify functions with SvelteKit,

  • how to configure a Netlify SvelteKit build,

  • how to add Netlify functions to your SvelteKit app.

If you want to create a static Netlify site for your next project, take a look at the post on SvelteKit static site HTTP headers. This post came from a question left in a comment. So if this post spurs further questions, please do drop a comment below and I might be able to create more content in response.

🙏🏽 Feedback

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