Why should you care?

Blocking the event loop waiting on MongoDB would freeze every Express request.

See it live — copy this example

Paste into your MeanVerse project (Angular + Express + MongoDB), then run with ng serve / node / mongosh as noted.

// Express handler with async/await
router.get('/accounts/:id', async (req, res, next) => {
  try {
    const account = await Account.findById(req.params.id).lean();
    if (!account) return res.status(404).json({ message: 'Not found' });
    res.json(account);
  } catch (err) {
    next(err);
  }
});

What happened?

• async function returns Promise.
• await pauses this handler until Mongoose resolves — other requests still run on the event loop.
• try/catch forwards DB errors to middleware.

Practice next

1. Convert one callback-style fs.readFile to readFile promise.
2. Write Express route with async/await and next(err).
3. Avoid await inside loops — use Promise.all for batch.
4. Wrap setTimeout in promisified delay(ms) helper.
5. Fetch three accounts with Promise.all and merge.

Remember

async/await is readable Promise syntax. Never block — always await I/O asynchronously. Express 5+ handles async errors; Express 4 needs try/catch.

Nightly statement job

MeanVerse batch generates 50k PDF statements without blocking API.

Outcome: Worker process uses async queue; API stays responsive.