Async error handling in routes in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an async route handler in Express.

Express

app.get('/data', async (req, res) => { const data = await fetchData(); res.send(data); });

app.get('/async', [1] (req, res) => { const result = await getResult(); res.json(result); });

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Afunction

Bawait

Casync

Dcallback

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add 'async' before the function causes syntax errors when using await.

Using 'await' outside an async function.

The route handler must be declared with 'async' to use await inside it.

2fill in blank

medium

Complete the code to catch errors in an async Express route using try-catch.

Express

app.get('/user', async (req, res) => {
  try {
    const user = await getUser(req.params.id);
    res.json(user);
  } catch ([1]) {
    res.status(500).send('Error fetching user');
  }
});

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Aerror

Be

Cerr

Dexception

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving the catch parameter empty causes syntax errors.

Using a variable name not declared in the catch block.

The catch block needs a variable to hold the error; 'e' is a common choice.

3fill in blank

hard

Fix the error in this async route by adding the missing error handler call.

Express

app.get('/items', async (req, res, next) => {
  const items = await fetchItems();
  res.json(items);
  [1]
});

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Areturn

Bthrow new Error()

Cnext(error)

Dnext()

Attempts:

3 left

💡 Hint

Common Mistakes

Not calling next() causes the request to hang.

Throwing errors without try-catch in async routes causes unhandled promise rejections.

Calling next() without arguments passes control to the next middleware, useful for error handling.

4fill in blank

hard

Fill both blanks to create an async route that forwards errors to Express error middleware.

Express

app.get('/profile', async (req, res, [1]) => {
  try {
    const profile = await getProfile(req.user.id);
    res.json(profile);
  } catch ([2]) {
    next(error);
  }
});

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Anext

Berr

Cerror

Dcallback

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names for next or error causes runtime errors.

Not calling next(error) inside catch blocks prevents error middleware from running.

The third parameter is 'next' to forward errors; the catch block error variable is 'error' to pass to next().

5fill in blank

hard

Fill all three blanks to create a reusable async error wrapper for Express routes.

Express

const asyncHandler = (fn) => (req, res, [1]) => {
  Promise.resolve(fn(req, res, next)).catch([2]);
};

app.get('/orders', asyncHandler(async (req, res) => {
  const orders = await getOrders();
  res.json(orders);
}));

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Anext

Berror

Derr

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names for next or error.

Not returning the Promise causes unhandled errors.

The wrapper uses 'next' as the third parameter and calls .catch(next) to forward errors.