Poll API for Asynchronous Job Status Updates

async function pollJobStatus(jobId, checkUrl, interval = 2000, maxAttempts = 30) {
  let attempts = 0;

  return new Promise((resolve, reject) => {
    const poll = async () => {
      if (attempts >= maxAttempts) {
        return reject(new Error(`Polling timed out after ${maxAttempts} attempts.`));
      }

      attempts++;
      try {
        const response = await fetch(`${checkUrl}/${jobId}`);
        if (!response.ok) {
          throw new Error(`Failed to fetch job status: ${response.statusText}`);
        }
        const data = await response.json();

        if (data.status === 'completed') {
          resolve(data);
        } else if (data.status === 'failed') {
          reject(new Error(`Job ${jobId} failed: ${data.errorMessage || 'Unknown error'}`));
        } else {
          // Job is still 'pending' or 'processing', poll again
          setTimeout(poll, interval);
        }
      } catch (error) {
        console.error(`Polling attempt ${attempts} failed:`, error);
        // Optionally, implement retry logic here with backoff
        setTimeout(poll, interval); // Retry on network error as well
      }
    };
    poll(); // Start the first poll immediately
  });
}

// Usage example:
// (async () => {
//   try {
//     // 1. Initiate an async job on your backend
//     // const startJobResponse = await fetch('/api/start-async-job', { method: 'POST' });
//     // const { jobId } = await startJobResponse.json();

//     const fakeJobId = 'abc-123'; // Assume you got this from a previous API call

//     console.log(`Starting to poll for job ${fakeJobId}...`);
//     const result = await pollJobStatus(fakeJobId, '/api/job-status', 1500, 20);
//     console.log('Job completed successfully:', result);
//     // Update UI with result
//   } catch (error) {
//     console.error('Job polling failed:', error.message);
//     // Show error to user
//   }
// })();

// Example backend endpoint structure for '/api/job-status/:jobId'
// GET /api/job-status/abc-123
// Responds with:
// { "jobId": "abc-123", "status": "processing", "progress": 50 }
// OR
// { "jobId": "abc-123", "status": "completed", "result": { "output": "processed data" } }
// OR
// { "jobId": "abc-123", "status": "failed", "errorMessage": "Input invalid" }