How to Fix CORS Errors in Svelte When Calling an API
Asked by
CuriousCoder42
I'm learning web development and I've run into some trouble with CORS errors while trying to call an API in my Svelte app. My intention is to make a POST request to an API and display the result on the page, but I'm hitting these CORS issues that are leaving me confused.
Here's a snippet from my +page.svelte file:
```typescript
interface PostData {
name: string;
value: string;
}
const apiUrl = 'https://api.example.com/search';
let postData: PostData = {
name: 'search_key',
value: 'search_word'
};
let responseData = null;
let errorMessage = '';
async function sendPostRequest() {
try {
const response = await fetch(apiUrl, {
method: 'POST',
headers: {
'Content-Type': 'application/json',
},
body: JSON.stringify(postData)
});
if (!response.ok) {
throw new Error(`HTTP error! Status: ${response.status}`);
}
responseData = await response.json();
errorMessage = '';
} catch (error) {
errorMessage = error.message || 'Failed to send request';
}
}
```
When I try this, I get CORS errors like:
```
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://api.example.com/search. (Reason: header 'access-control-allow-methods' is not allowed according to header 'Access-Control-Allow-Headers' from CORS preflight response).
```
I've tested the API using Postman and it works fine. It's confusing why I'm facing this issue in Svelte when it appears to be working as expected in other environments. Any guidance on how to fix this would be hugely appreciated!
Answers
The CORS errors you're facing are often due to backend configurations on the API you're trying to access. Since you don’t control this API, you might not be able to fix it directly. Typically, you'd need to ensure your frontend URL is allowed by the backend's CORS settings. If it doesn't allow your origin, you won't be able to access it directly from the browser.
Reply to this answer
Yeah, you've hit the nail on the head! CORS issues are a browser security feature. The good news is there are a couple of ways to get around this. First, if you have a way to configure the API server, ask the owner to add your site as an allowed origin. If not, setting up a proxy server to handle your API requests might be the way to go. You send calls to your proxy, which then communicates with the API for you, essentially acting as a middleman.
CuriousCoder42: Thanks for that! I did create a simple Express proxy, which resolved some preflight issues, but I'm still getting some errors. What could be going wrong?
Reply to this answer
Ultimately, the issue may be with how the API itself is set up. If the API is returning a wildcard for CORS, check that you're not sending restrictive headers. For instance, removing headers like 'Content-Type' might allow your request to go through since it wouldn't trigger a CORS preflight check. Just be sure to check the API documentation for any restrictions or requirements on the requests!
Reply to this answer
You definitely need a CORS proxy to overcome these sorts of issues. One popular option is 'cors-anywhere', which can help. You can also set up your own simple proxy server in any backend language you prefer. For straightforward GET requests, it’s usually not too complex.
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TechSupportTim: But what if the backend is public and I have no access? Can I use a proxy instead?