Unhandled Promise Rejections in Node.js are causing crashes or silent failures

In my Node.js application, sometimes an asynchronous function (e.g. a file read or HTTP request) fails, and my app either crashes or silently ignores the error. Why does this happen and how can I prevent it?

The root cause is usually an unhandled promise rejection, where a promise throws an error that isn’t caught by a .catch() block or by try…catch in an async function. 🔎 Why it happens: • Promises or async functions that reject but don’t have .catch() or try/catch lead to: o UncaughtPromiseRejectionWarning or default crashing (in recent Node versions). o Silent failures where the flow continues without handling the error arXiv+3devspeaks.com+3how-is-my-backend.whiteloves.in+3CBT Nuggets. • Streams that emit error events without listeners can crash the process LogRocket Blog.

🛠️ How to fix it Practice Description Use try/catch with async/await Always wrap your async logic:
try { await asyncFn(); } catch (err) { handleError(err); } Attach .catch() to Promises Always: promiseFunction().then(...).catch(err ⇒ { /* handle */ }); Use global handlers (backup) For safety, set up: js CopyEdit process.on('unhandledRejection', err => { console.error('Unhandled rejection:', err); // optional cleanup & exit }); process.on('uncaughtException', err => { console.error('Uncaught exception:', err); process.exit(1); });

| **Attach error handlers to streams** | Always: `<stream>.on('error', err ⇒ { /* handle or close */ });` to prevent crashes :contentReference[oaicite:15]{index=15} |

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### 🧩 **Real-world Example**

```js
// ❌ BAD: Missing .catch()
fetchUrl('https://api.example.com/data')
  .then(processData);

// ✅ FIX: Proper error handling
fetchUrl('https://api.example.com/data')
  .then(processData)
  .catch(err => console.error('Fetch failed:', err));
Or using async:
js
CopyEdit
async function runTask() {
  try {
    const result = await fetchUrl(url);
    await processData(result);
  } catch (err) {
    console.error('Error in runTask:', err);
  }
}
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👀 Additional Recommendations
•	Use linting tools like ESLint with rules that catch unhandled rejections.
•	Prefer structured error handling using async/await and uniform .catch() blocks.
•	Use monitoring/logging tools to detect unhandled failures in production early.