refetch or poll an external api with fetch in svelte - api

Question

New to Svelte and am running into some issues.
Currently doing the following in +page.server.js
I would like to poll this API every couple hundred milliseconds, I am unsure how to do that. I have tried using set Interval here to no avail.
export async function load({params}) {
const response = await fetch(
`http://localhost:9595/api/v1/chrysalis/example?uid=${params.uid}`
)
const site = await response.json()
const siteData = site[0]
console.log(siteData)
return {
uid: params.uid,
partitions: siteData.partitions,
zones: siteData.zones,
zTypes: siteData.zTypes,
zStates: siteData.zStates,
zNames: siteData.zNames
}
}
For example, I've built this in next.Js using SWR with refreshInterval: 1.
const {data, error, isLoading} = useSWR(
'http://localhost:9595/api/v1/chrysalis/example',
(url) => {
const searchParams = new URLSearchParams();
searchParams.append("uid", body.uid)
const newUrl = `${url}?${searchParams.toString()}`
const options = {
method: 'GET',
headers: {'Content-Type': 'application/json'},
}
return fetch(newUrl, options).then(res => res.json())
},
{
refreshInterval: 1
}
);
I have also tried to do the following onMount of the +page.svelte but when trying to hit the API from the client I get CORS error.( ran into this before if +page.js was not +page.server.js
let x;
onMount(async () => {
setInterval(async () => {
const response = await fetch(
`http://localhost:9595/api/v1/chrysalis/example?uid=${data.uid}`
)
const site = await response.json()
x = site[0]
console.log(x)
}, 3000)
})

Answer 1

The CORS error results because +page.svelte/+page.js are run in the browser. So you need to proxy the call through a service that allows being called from the browser. (Or relax the CORS restrictions on http://localhost:9595)
You can use SvelteKit itself to proxy the call by creating an internal endpoint. So:
The internal endpoint simply fetches http://localhost:9595/... and returns the results. (You can just forward the response object from fetch())
+page.svelte calls that internal endpoint from setInterval().