JavaScript API Polling with Interval Control

/**
 * Creates a controllable API polling mechanism.
 * @param {function(): Promise<any>} fetchCallback - An async function that performs the API fetch and returns data.
 * @param {number} intervalMs - The polling interval in milliseconds.
 * @param {function(any): void} successCallback - Callback function for successful data fetches.
 * @param {function(Error): void} errorCallback - Callback function for fetch errors.
 * @returns {{start: Function, stop: Function, isRunning: Function, setInterval: Function}} Controls for the polling.
 */
function createApiPolling(fetchCallback, intervalMs, successCallback, errorCallback) {
  let intervalId = null;
  let currentIntervalMs = intervalMs;
  let running = false;

  const poll = async () => {
    try {
      const data = await fetchCallback();
      successCallback(data);
    } catch (error) {
      errorCallback(error);
    }
  };

  const start = () => {
    if (!running) {
      running = true;
      // Run immediately once, then start interval
      poll();
      intervalId = setInterval(poll, currentIntervalMs);
      console.log(`API polling started with interval: ${currentIntervalMs}ms`);
    }
  };

  const stop = () => {
    if (running) {
      clearInterval(intervalId);
      intervalId = null;
      running = false;
      console.log('API polling stopped.');
    }
  };

  const setInterval = (newIntervalMs) => {
    if (newIntervalMs <= 0) {
      console.warn('Polling interval must be greater than 0ms.');
      return;
    }
    currentIntervalMs = newIntervalMs;
    if (running) {
      stop();
      start(); // Restart with new interval
    }
    console.log(`Polling interval updated to: ${currentIntervalMs}ms`);
  };

  const isRunning = () => running;

  return { start, stop, isRunning, setInterval };
}

// Example Usage:
// Simulate an API call that sometimes fails
// let callCount = 0;
// const mockApiFetch = async () => {
//   callCount++;
//   console.log(`Mock API call #${callCount}...`);
//   return new Promise((resolve, reject) => {
//     setTimeout(() => {
//       if (Math.random() > 0.2) { // 80% success rate
//         resolve({ status: 'ok', timestamp: new Date().toISOString(), value: Math.random() * 100 });
//       } else {
//         reject(new Error('Mock API error: Could not fetch data.'));
//       }
//     }, 500); // Simulate network latency
//   });
// };

// const handleSuccess = (data) => console.log('Polling success:', data);
// const handleError = (error) => console.error('Polling error:', error.message);

// const poller = createApiPolling(mockApiFetch, 3000, handleSuccess, handleError);

// // Start polling after 1 second
// setTimeout(() => {
//   poller.start();
// }, 1000);

// // Change interval after 10 seconds
// setTimeout(() => {
//   poller.setInterval(1500);
// }, 10000);

// // Stop polling after 20 seconds
// setTimeout(() => {
//   poller.stop();
// }, 20000);