TIL: How to fix structuredClone to work on Netlify SvelteKit Site

Recently I was working on my SvelteKit site and added some code like so to my hook.server.ts:

try {
    if (event.locals.pb.authStore.isValid) {
        await event.locals.pb.collection("users").authRefresh();
        event.locals.user = structuredClone(event.locals.pb?.authStore.model);
} catch (err) {
    console.log("failed to refresh auth", err);
    event.locals.user = undefined;

I needed to add the structuredClone function so that only POJO (plain old javascript objects) would get stored in the event.locals.users variable. However when I deployed this to production in Netlify. This broke my site! Specifically, it wouldn’t let the user log in.

If you deploy your SvelteKit app on Netlify the server-side code gets turned into functions for us automagically! I was able to work out that structuredClone function broke my app because in my login function I could see something like:

ReferenceError: structuredClone is not defined

Netlify Functions

It seems that the structuredClone was only added in nodejs 17 1. However, Netlify functions default to nodejs 16.

For all Node.js functions deployed on or after July 11, 2022, Netlify uses Node.js 16 as the default runtime. - https://docs.netlify.com/functions/optional-configuration/?fn-language=js

Reading the docs we can see if we set the AWS_LAMBDA_JS_RUNTIME in the GUI to nodejs18.x this will force our functions to use nodejs 18.

Netlify Builds Vars

And that’s it! By setting our nodejs version to 18, we will be able to use the structuredClone function.