# Step 1 — Check the Browser Console

Open your browser’s developer tools:

• Chrome: F12 → Console

• Firefox: F12 → Console

Look for:

• TypeError: Failed to fetch

• SyntaxError: Unexpected token

• HTTP status codes (404, 500, etc.)

---

## Step 2 — Verify the URL

The most common fetch error is an incorrect or unreachable URL:

fetch('https://api.example.com/data')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error('Fetch error:', error));

Tips:

• Ensure the URL is correct

• Include the full protocol (http:// or https://)

• Check that the server is running and accessible

Test the URL in the browser or using curl:

curl -I https://api.example.com/data

---

## Step 3 — Handle HTTP Status Codes

fetch only rejects on network errors. A 404 or 500 does not throw automatically.

fetch('https://api.example.com/data')
  .then(response => {
    if (!response.ok) {
      throw new Error(`HTTP error! Status: ${response.status}`);
    }
    return response.json();
  })
  .then(data => console.log(data))
  .catch(error => console.error('Fetch error:', error));

• response.ok → true for 200–299 responses

• Properly handling status codes prevents silent failures

---

## Step 4 — Check CORS Issues

A common fetch error in the browser is a CORS (Cross-Origin Resource Sharing) block:

Access to fetch at 'https://api.example.com/data' from origin 'http://localhost:3000' has been blocked by CORS policy

Solution:

• Enable CORS on your backend (allow your frontend origin)

• Use full backend paths

• For development, a proxy can bypass CORS temporarily

---

## Step 5 — Handle JSON Parsing Errors

Sometimes the response isn’t valid JSON:

fetch('https://api.example.com/data')
  .then(response => response.text()) // use text() to debug
  .then(text => console.log(text))
  .catch(error => console.error('Fetch error:', error));

Tips:

• Confirm the response content-type is application/json

• Wrap response.json() in try/catch

fetch('https://api.example.com/data')
  .then(async response => {
    try {
      const data = await response.json();
      console.log(data);
    } catch (err) {
      console.error('Invalid JSON:', err);
    }
  });

---

## Step 6 — Check Network Connectivity

• Ensure your machine is online

• Check firewall or VPN settings

• Verify server is reachable with ping or curl

---

## Step 7 — Debug Using Developer Tools Network Tab

• Open DevTools → Network Tab

• Reload the page

• Look at the request:

  • Status code

  • Response body

  • Request headers

  • Any redirect issues

This gives clues for misconfigurations or server errors.

---

## Step 8 — Use Proper Headers

Some APIs require headers:

fetch('https://api.example.com/data', {
  method: 'GET',
  headers: {
    'Authorization': 'Bearer YOUR_API_KEY',
    'Content-Type': 'application/json'
  }
})

• Missing required headers → fetch may fail

• Check API documentation

---

## Step 9 — Retry or Fallback

For network instability, add retry logic:

async function fetchWithRetry(url, retries = 3) {
  for (let i = 0; i < retries; i++) {
    try {
      const response = await fetch(url);
      if (!response.ok) throw new Error(`Status ${response.status}`);
      return await response.json();
    } catch (err) {
      console.error(`Attempt ${i + 1} failed:`, err);
    }
  }
  throw new Error('All fetch attempts failed');
}

fetchWithRetry('https://api.example.com/data').then(data => console.log(data));

---

## Step 10 — Beginner-Friendly Checklist

---

## Conclusion

JavaScript fetch errors are common, especially for beginners, but they can be fixed by systematically:

• Checking the browser console

• Verifying URLs and network connectivity

• Handling HTTP status codes and JSON parsing

• Resolving CORS issues

• Using proper headers and retries

Following these steps, even beginners can troubleshoot fetch errors effectively and ensure smooth communication between frontend and backend.