How do you implement a background job scheduler in Node.js?

Question

Accepted Answer

**Job scheduler** — runs tasks at specific times or intervals.

```javascript
const cron = require("node-cron");

// Run every day at midnight
cron.schedule("0 0 * * *", async () => {
    console.log("Running daily cleanup...");
    await cleanupExpiredSessions();
    await generateDailyReport();
});

// Run every 5 minutes
cron.schedule("*/5 * * * *", async () => {
    await syncExternalData();
});

// With error handling
cron.schedule("0 * * * *", async () => {
    try {
        await processQueue();
    } catch (err) {
        console.error("Job failed:", err);
        await notifyAdmin(err);
    }
});
```

**Using BullMQ (distributed):**
```javascript
const { Queue, Worker } = require("bullmq");

const cleanupQueue = new Queue("cleanup");

// Add delayed job
await cleanupQueue.add("daily-cleanup", {}, {
    repeat: { cron: "0 0 * * *" },
});

const worker = new Worker("cleanup", async (job) => {
    await cleanupExpiredSessions();
});
```

**Key points:**
- node-cron for single process.
- BullMQ for distributed scheduling.
- Handle failures and retries.

Node.js: How do you implement a background job scheduler in Node.js?